The For...Next Loop
The For...Next Loop is another way to make loops in Visual Basic. For...Next repetition structure handles all the details of counter-controlled repetition. The following loop counts the numbers from 1 to 100:
Dim x As Integer
For x = 1 To 50
Print x
Next
In order to count the numbers from 1 yo 50 in steps of 2, the following loop can be used
For x = 1 To 50 Step 2
Print x
Next
The following loop counts numbers as 1, 3, 5, 7..etc
The above coding will display numbers vertically on the form. In order to display numbers horizontally the following method can be used.
For x = 1 To 50
Print x & Space$ (2);
Next
To increase the space between the numbers increase the value inside the brackets after the & Space$.
Following example is a For...Next repetition structure which is with the If condition used.
Dim number As Integer
For number = 1 To 10
If number = 4 Then
Print "This is number 4"
Else
Print number
End If
Next
In the output instead of number 4 you will get the "This is number 4".
Thursday, August 27, 2009
Loop in Visual basic
The Do While...Loop is used to execute statements until a certain condition is met. The following Do Loop counts from 1 to 100.
Dim number As Integer
number = 1
Do While number <= 100
number = number + 1
Loop
A variable number is initialized to 1 and then the Do While Loop starts. First, the condition is tested; if condition is True, then the statements are executed. When it gets to the Loop it goes back to the Do and tests condition again. If condition is False on the first pass, the statements are never executed.
While... Wend Statement
A While...Wend statement behaves like the Do While...Loop statement. The following While...Wend counts from 1 to 100
Dim number As Integer
number = 1
While number <=100
number = number + 1
Wend
Do...Loop While Statement
The Do...Loop While statement first executes the statements and then test the condition after each execution. The following program block illustrates the structure:
Dim number As Long
number = 0
Do
number = number + 1
Loop While number < 201
The programs executes the statements between Do and Loop While structure in any case. Then it determines whether the counter is less than 501. If so, the program again executes the statements between Do and Loop While else exits the Loop.
Do Until...Loop Statement
Unlike the Do While...Loop and While...Wend repetition structures, the Do Until... Loop structure tests a condition for falsity. Statements in the body of a Do Until...Loop are executed repeatedly as long as the loop-continuation test evaluates to False.
An example for Do Until...Loop statement. The coding is typed inside the click event of the command button
Dim number As Long
number=0
Do Until number > 1000
number = number + 1
Print number
Loop
Numbers between 1 to 1000 will be displayed on the form as soon as you click on the command button.
Dim number As Integer
number = 1
Do While number <= 100
number = number + 1
Loop
A variable number is initialized to 1 and then the Do While Loop starts. First, the condition is tested; if condition is True, then the statements are executed. When it gets to the Loop it goes back to the Do and tests condition again. If condition is False on the first pass, the statements are never executed.
While... Wend Statement
A While...Wend statement behaves like the Do While...Loop statement. The following While...Wend counts from 1 to 100
Dim number As Integer
number = 1
While number <=100
number = number + 1
Wend
Do...Loop While Statement
The Do...Loop While statement first executes the statements and then test the condition after each execution. The following program block illustrates the structure:
Dim number As Long
number = 0
Do
number = number + 1
Loop While number < 201
The programs executes the statements between Do and Loop While structure in any case. Then it determines whether the counter is less than 501. If so, the program again executes the statements between Do and Loop While else exits the Loop.
Do Until...Loop Statement
Unlike the Do While...Loop and While...Wend repetition structures, the Do Until... Loop structure tests a condition for falsity. Statements in the body of a Do Until...Loop are executed repeatedly as long as the loop-continuation test evaluates to False.
An example for Do Until...Loop statement. The coding is typed inside the click event of the command button
Dim number As Long
number=0
Do Until number > 1000
number = number + 1
Print number
Loop
Numbers between 1 to 1000 will be displayed on the form as soon as you click on the command button.
Tuesday, August 25, 2009
DriveListBox, DirListBox, and FileListBox Controls in vb 6
Three of the controls on the ToolBox let you access the computer's file system. They are DriveListBox, DirListBox and FileListBox controls (see below figure) , which are the basic blocks for building dialog boxes that display the host computer's file system. Using these controls, user can traverse the host computer's file system, locate any folder or files on any hard disk, even on network drives. The files are controls are independent of one another, and each can exist on it's own, but they are rarely used separately. The files controls are described next.
In a nutshell, the DriveListBox control is a combobox-like control that's automatically filled with your drive's letters and volume labels. The DirListBox is a special list box that displays a directory tree. The FileListBox control is a special-purpose ListBox control that displays all the files in a given directory, optionally filtering them based on their names, extensions, and attributes.
These controls often work together on the same form; when the user selects a drive in a DriveListBox, the DirListBox control is updated to show the directory tree on that drive. When the user selects a path in the DirListBox control, the FileListBox control is filled with the list of files in that directory. These actions don't happen automatically, however—you must write code to get the job done.
After you place a DriveListBox and a DirListBox control on a form's surface, you usually don't have to set any of their properties; in fact, these controls don't expose any special property, not in the Properties window at least. The FileListBox control, on the other hand, exposes one property that you can set at design time—the Pattern property. This property indicates which files are to be shown in the list area: Its default value is *.* (all files), but you can enter whatever specification you need, and you can also enter multiple specifications using the semicolon as a separator. You can also set this property at run time, as in the following line of code:
File1.Pattern = "*.txt;*.doc;*.rtf"
Following figure shows three files controls are used in the design of Forms that let users explore the entire structure of their hard disks.
DriveListBox : Displays the names of the drives within and connected to the PC. The basic property of this control is the drive property, which set the drive to be initially selected in the control or returns the user's selection.
DirListBox : Displays the folders of current Drive. The basic property of this control is the Path property, which is the name of the folder whose sub folders are displayed in the control.
FileListBox : Displays the files of the current folder. The basic property of this control is also called Path, and it's the path name of the folder whose files are displayed.
The three File controls are not tied to one another. If you place all three of them on a Form, you will see the names of all the folders under the current folder, and so on. Each time you select a folder in the DirlistBox by double clicking its name, its sub folders are displayed. Similarly , the FileListBox control will display the names of all files in the current folder. Selecting a drive in the DriveListBox control, however this doesn't affect the contents of the DirListBox.
To connect to the File controls, you must assign the appropriate values to the properties. To compel the DirListBox to display the folders of the selected drive in the DriveListBox, you must make sure that each time the user selects another drive, the Path property of the DirListBox control matches the Drive property of the DriveListBox.
After these preliminary steps, you're ready to set in motion the chain of events. When the user selects a new drive in the DriveListBox control, it fires a Change event and returns the drive letter (and volume label) in its Drive property. You trap this event and set the DirListBox control's Path property to point to the root directory of the selected drive:
Private Sub Drive1_Change()
' The Drive property also returns the volume label, so trim it.
Dir1.Path = Left$(Drive1.Drive, 1) & ":\"
End Sub
When the user double-clicks on a directory name, the DirListBox control raises a Change event; you trap this event to set the FileListBox's Path property accordingly:
Private Sub Dir1_Change()
File1.Path = Dir1.Path
End Sub
Finally, when the user clicks on a file in the FileListBox control, a Click event is fired (as if it were a regular ListBox control), and you can query its Filename property to learn which file has been selected. Note how you build the complete path:
Filename = File1.Path
If Right$(Filename, 1) <> "\" Then Filename = Filename & "\"
Filename = Filename & File1.Filename
The DirListBox and FileListBox controls support most of the properties typical of the control they derive from—the ListBox control—including the ListCount and the ListIndex properties and the Scroll event. The FileListBox control supports multiple selection; hence you can set its MultiSelect property in the Properties window and query the SelCount and Selected properties at run time.
The FileListBox control also exposes a few custom Boolean properties, Normal, Archive, Hidden, ReadOnly, and System, which permit you to decide whether files with these attributes should be listed. (By default, the control doesn't display hidden and system files.) This control also supports a couple of custom events, PathChange and PatternChange, that fire when the corresponding property is changed through code. In most cases, you don't have to worry about them, and I won't provide examples of their usage.
The problem with the DriveListBox, DirListBox and FileListBox controls is that they're somewhat outdated and aren't used by most commercial applications any longer. Moreover, these controls are known to work incorrectly when listing files on network servers and sometimes even on local disk drives, especially when long file and directory names are used. For this reason, I discourage you from using them and suggest instead that you use the Common Dialog controls for your FileOpen and FileSave dialog boxes. But if you need to ask the user for the name of a directory rather than a file, you're out of luck because—while Windows does include such a system dialog box, named BrowseForFolders dialog—Visual Basic still doesn't offer a way to display it (unless you do some advanced API programming). Fortunately, Visual Basic 6 comes with a new control—the ImageCombo control—that lets you simulate the appearance of the DriveListBox control. It also offers you a powerful library—the FileSystemObject library—that completely frees you from using these three controls, if only as hidden controls that you use just for quickly retrieving information on the file system.
In a nutshell, the DriveListBox control is a combobox-like control that's automatically filled with your drive's letters and volume labels. The DirListBox is a special list box that displays a directory tree. The FileListBox control is a special-purpose ListBox control that displays all the files in a given directory, optionally filtering them based on their names, extensions, and attributes.
These controls often work together on the same form; when the user selects a drive in a DriveListBox, the DirListBox control is updated to show the directory tree on that drive. When the user selects a path in the DirListBox control, the FileListBox control is filled with the list of files in that directory. These actions don't happen automatically, however—you must write code to get the job done.
After you place a DriveListBox and a DirListBox control on a form's surface, you usually don't have to set any of their properties; in fact, these controls don't expose any special property, not in the Properties window at least. The FileListBox control, on the other hand, exposes one property that you can set at design time—the Pattern property. This property indicates which files are to be shown in the list area: Its default value is *.* (all files), but you can enter whatever specification you need, and you can also enter multiple specifications using the semicolon as a separator. You can also set this property at run time, as in the following line of code:
File1.Pattern = "*.txt;*.doc;*.rtf"
Following figure shows three files controls are used in the design of Forms that let users explore the entire structure of their hard disks.
DriveListBox : Displays the names of the drives within and connected to the PC. The basic property of this control is the drive property, which set the drive to be initially selected in the control or returns the user's selection.
DirListBox : Displays the folders of current Drive. The basic property of this control is the Path property, which is the name of the folder whose sub folders are displayed in the control.
FileListBox : Displays the files of the current folder. The basic property of this control is also called Path, and it's the path name of the folder whose files are displayed.
The three File controls are not tied to one another. If you place all three of them on a Form, you will see the names of all the folders under the current folder, and so on. Each time you select a folder in the DirlistBox by double clicking its name, its sub folders are displayed. Similarly , the FileListBox control will display the names of all files in the current folder. Selecting a drive in the DriveListBox control, however this doesn't affect the contents of the DirListBox.
To connect to the File controls, you must assign the appropriate values to the properties. To compel the DirListBox to display the folders of the selected drive in the DriveListBox, you must make sure that each time the user selects another drive, the Path property of the DirListBox control matches the Drive property of the DriveListBox.
After these preliminary steps, you're ready to set in motion the chain of events. When the user selects a new drive in the DriveListBox control, it fires a Change event and returns the drive letter (and volume label) in its Drive property. You trap this event and set the DirListBox control's Path property to point to the root directory of the selected drive:
Private Sub Drive1_Change()
' The Drive property also returns the volume label, so trim it.
Dir1.Path = Left$(Drive1.Drive, 1) & ":\"
End Sub
When the user double-clicks on a directory name, the DirListBox control raises a Change event; you trap this event to set the FileListBox's Path property accordingly:
Private Sub Dir1_Change()
File1.Path = Dir1.Path
End Sub
Finally, when the user clicks on a file in the FileListBox control, a Click event is fired (as if it were a regular ListBox control), and you can query its Filename property to learn which file has been selected. Note how you build the complete path:
Filename = File1.Path
If Right$(Filename, 1) <> "\" Then Filename = Filename & "\"
Filename = Filename & File1.Filename
The DirListBox and FileListBox controls support most of the properties typical of the control they derive from—the ListBox control—including the ListCount and the ListIndex properties and the Scroll event. The FileListBox control supports multiple selection; hence you can set its MultiSelect property in the Properties window and query the SelCount and Selected properties at run time.
The FileListBox control also exposes a few custom Boolean properties, Normal, Archive, Hidden, ReadOnly, and System, which permit you to decide whether files with these attributes should be listed. (By default, the control doesn't display hidden and system files.) This control also supports a couple of custom events, PathChange and PatternChange, that fire when the corresponding property is changed through code. In most cases, you don't have to worry about them, and I won't provide examples of their usage.
The problem with the DriveListBox, DirListBox and FileListBox controls is that they're somewhat outdated and aren't used by most commercial applications any longer. Moreover, these controls are known to work incorrectly when listing files on network servers and sometimes even on local disk drives, especially when long file and directory names are used. For this reason, I discourage you from using them and suggest instead that you use the Common Dialog controls for your FileOpen and FileSave dialog boxes. But if you need to ask the user for the name of a directory rather than a file, you're out of luck because—while Windows does include such a system dialog box, named BrowseForFolders dialog—Visual Basic still doesn't offer a way to display it (unless you do some advanced API programming). Fortunately, Visual Basic 6 comes with a new control—the ImageCombo control—that lets you simulate the appearance of the DriveListBox control. It also offers you a powerful library—the FileSystemObject library—that completely frees you from using these three controls, if only as hidden controls that you use just for quickly retrieving information on the file system.
Label
Label and Frame controls have a few features in common, so it makes sense to explain them together. First they're mostly "decorative" controls that contribute to the user interface but are seldom used as programmable objects. In other words, you often place them on the form and arrange their properties as your user interface needs dictate, but you rarely write code to serve their events, generally, or manipulate their properties at run time.
Label Controls
Most people use Label controls to provide a descriptive caption and possibly an associated hot key for other controls, such as TextBox, ListBox, and ComboBox, that don't expose the Caption property. In most cases, you just place a Label control where you need it, set its Caption property to a suitable string (embedding an ampersand character in front of the hot key you want to assign), and you're done. Caption is the default property for Label controls. Be careful to set the Label's TabIndex property so that it's 1 minus the TabIndex property of the companion control.
Other useful properties are BorderStyle(if you want the Label control to appear inside a 3D border) and Alignment (if you want to align the caption to the right or center it on the control). In most cases, the alignment depends on how the Label control relates to its companion control: for example, if the Label control is placed to the left of its companion field, you might want to set its Alignment property to 1-Right Justify. The value 2-Center is especially useful for stand-alone Label controls.
Label Controls
Most people use Label controls to provide a descriptive caption and possibly an associated hot key for other controls, such as TextBox, ListBox, and ComboBox, that don't expose the Caption property. In most cases, you just place a Label control where you need it, set its Caption property to a suitable string (embedding an ampersand character in front of the hot key you want to assign), and you're done. Caption is the default property for Label controls. Be careful to set the Label's TabIndex property so that it's 1 minus the TabIndex property of the companion control.
Other useful properties are BorderStyle(if you want the Label control to appear inside a 3D border) and Alignment (if you want to align the caption to the right or center it on the control). In most cases, the alignment depends on how the Label control relates to its companion control: for example, if the Label control is placed to the left of its companion field, you might want to set its Alignment property to 1-Right Justify. The value 2-Center is especially useful for stand-alone Label controls.
Frame Controls
Frame Controls
Frame controls are similar to Label controls in that they can serve as captions for those controls that don't have their own. Moreover, Frame controls can also (and often do) behave as containers and host other controls. In most cases, you only need to drop a Frame control on a form and set its Caption property. If you want to create a borderless frame, you can set its BorderStyle property to 0-None.
Controls that are contained in the Frame control are said to be child controls. Moving a control at design time over a Frame control—or over any other container, for that matter—doesn't automatically make that control a child of the Frame control. After you create a Frame control, you can create a child control by selecting the child control's icon in the Toolbox and drawing a new instance inside the Frame's border. Alternatively, to make an existing control a child of a Frame control, you must select the control, press Ctrl+X to cut it to the Clipboard, select the Frame control, and press Ctrl+V to paste the control inside the Frame. If you don't follow this procedure and you simply move the control over the Frame, the two controls remain completely independent of each other, even if the other control appears in front of the Frame control.
Frame controls, like all container controls, have two interesting features. If you move a Frame control, all the child controls go with it. If you make a container control disabled or invisible, all its child controls also become disabled or invisible. You can exploit these features to quickly change the state of a group of related controls.
Frame controls are similar to Label controls in that they can serve as captions for those controls that don't have their own. Moreover, Frame controls can also (and often do) behave as containers and host other controls. In most cases, you only need to drop a Frame control on a form and set its Caption property. If you want to create a borderless frame, you can set its BorderStyle property to 0-None.
Controls that are contained in the Frame control are said to be child controls. Moving a control at design time over a Frame control—or over any other container, for that matter—doesn't automatically make that control a child of the Frame control. After you create a Frame control, you can create a child control by selecting the child control's icon in the Toolbox and drawing a new instance inside the Frame's border. Alternatively, to make an existing control a child of a Frame control, you must select the control, press Ctrl+X to cut it to the Clipboard, select the Frame control, and press Ctrl+V to paste the control inside the Frame. If you don't follow this procedure and you simply move the control over the Frame, the two controls remain completely independent of each other, even if the other control appears in front of the Frame control.
Frame controls, like all container controls, have two interesting features. If you move a Frame control, all the child controls go with it. If you make a container control disabled or invisible, all its child controls also become disabled or invisible. You can exploit these features to quickly change the state of a group of related controls.
Frame Controls
Frame Controls
Frame controls are similar to Label controls in that they can serve as captions for those controls that don't have their own. Moreover, Frame controls can also (and often do) behave as containers and host other controls. In most cases, you only need to drop a Frame control on a form and set its Caption property. If you want to create a borderless frame, you can set its BorderStyle property to 0-None.
Controls that are contained in the Frame control are said to be child controls. Moving a control at design time over a Frame control—or over any other container, for that matter—doesn't automatically make that control a child of the Frame control. After you create a Frame control, you can create a child control by selecting the child control's icon in the Toolbox and drawing a new instance inside the Frame's border. Alternatively, to make an existing control a child of a Frame control, you must select the control, press Ctrl+X to cut it to the Clipboard, select the Frame control, and press Ctrl+V to paste the control inside the Frame. If you don't follow this procedure and you simply move the control over the Frame, the two controls remain completely independent of each other, even if the other control appears in front of the Frame control.
Frame controls, like all container controls, have two interesting features. If you move a Frame control, all the child controls go with it. If you make a container control disabled or invisible, all its child controls also become disabled or invisible. You can exploit these features to quickly change the state of a group of related controls.
Frame controls are similar to Label controls in that they can serve as captions for those controls that don't have their own. Moreover, Frame controls can also (and often do) behave as containers and host other controls. In most cases, you only need to drop a Frame control on a form and set its Caption property. If you want to create a borderless frame, you can set its BorderStyle property to 0-None.
Controls that are contained in the Frame control are said to be child controls. Moving a control at design time over a Frame control—or over any other container, for that matter—doesn't automatically make that control a child of the Frame control. After you create a Frame control, you can create a child control by selecting the child control's icon in the Toolbox and drawing a new instance inside the Frame's border. Alternatively, to make an existing control a child of a Frame control, you must select the control, press Ctrl+X to cut it to the Clipboard, select the Frame control, and press Ctrl+V to paste the control inside the Frame. If you don't follow this procedure and you simply move the control over the Frame, the two controls remain completely independent of each other, even if the other control appears in front of the Frame control.
Frame controls, like all container controls, have two interesting features. If you move a Frame control, all the child controls go with it. If you make a container control disabled or invisible, all its child controls also become disabled or invisible. You can exploit these features to quickly change the state of a group of related controls.
OptionButton Controls in VB6
OptionButton Controls in VB6
OptionButton controls are also known as radio buttons because of their shape. You always use OptionButton controls in a group of two or more because their purpose is to offer a number of mutually exclusive choices. Anytime you click on a button in the group, it switches to a selected state and all the other controls in the group become unselected.
Preliminary operations for an OptionButton control are similar to those already described for CheckBox controls. You set an OptionButton control's Caption property to a meaningful string, and if you want you can change its Alignment property to make the control right aligned. If the control is the one in its group that's in the selected state, you also set its Valueproperty to True. (The OptionButton's Value property is a Boolean value because only two states are possible.) Value is the default property for this control.
At run time, you typically query the control's Value property to learn which button in its group has been selected. Let's say you have three OptionButton controls, named optWeekly, optMonthly, and optYearly. You can test which one has been selected by the user as follows:
If optWeekly.Value Then
' User prefers weekly frequency.
ElseIf optMonthly.Value Then
' User prefers monthly frequency.
ElseIf optYearly.Value Then
' User prefers yearly frequency.
End If
Strictly speaking, you can avoid the test for the last OptionButton control in its group because all choices are supposed to be mutually exclusive. But the approach I just showed you increases the code's readability.
A group of OptionButton controls is often hosted in a Frame control. This is necessary when there are other groups of OptionButton controls on the form. As far as Visual Basic is concerned, all the OptionButton controls on a form's surface belong to the same group of mutually exclusive selections, even if the controls are placed at the opposite corners of the window. The only way to tell Visual Basic which controls belong to which group is by gathering them inside a Frame control. Actually, you can group your controls within any control that can work as a container—PictureBox, for example—but Frame controls are often the most reasonable choice.
OptionButton controls are also known as radio buttons because of their shape. You always use OptionButton controls in a group of two or more because their purpose is to offer a number of mutually exclusive choices. Anytime you click on a button in the group, it switches to a selected state and all the other controls in the group become unselected.
Preliminary operations for an OptionButton control are similar to those already described for CheckBox controls. You set an OptionButton control's Caption property to a meaningful string, and if you want you can change its Alignment property to make the control right aligned. If the control is the one in its group that's in the selected state, you also set its Valueproperty to True. (The OptionButton's Value property is a Boolean value because only two states are possible.) Value is the default property for this control.
At run time, you typically query the control's Value property to learn which button in its group has been selected. Let's say you have three OptionButton controls, named optWeekly, optMonthly, and optYearly. You can test which one has been selected by the user as follows:
If optWeekly.Value Then
' User prefers weekly frequency.
ElseIf optMonthly.Value Then
' User prefers monthly frequency.
ElseIf optYearly.Value Then
' User prefers yearly frequency.
End If
Strictly speaking, you can avoid the test for the last OptionButton control in its group because all choices are supposed to be mutually exclusive. But the approach I just showed you increases the code's readability.
A group of OptionButton controls is often hosted in a Frame control. This is necessary when there are other groups of OptionButton controls on the form. As far as Visual Basic is concerned, all the OptionButton controls on a form's surface belong to the same group of mutually exclusive selections, even if the controls are placed at the opposite corners of the window. The only way to tell Visual Basic which controls belong to which group is by gathering them inside a Frame control. Actually, you can group your controls within any control that can work as a container—PictureBox, for example—but Frame controls are often the most reasonable choice.
Monday, August 24, 2009
VB6 CommandButton
When compared to TextBox controls, these controls are really simple. Not only do they expose relatively few properties, they also support a limited number of events, and you don't usually write much code to manage them.
CommandButton Controls in VB6
Using CommandButton controls is trivial. In most cases, you just draw the control on the form's surface, set its Caption property to a suitable string (adding an & character to associate a hot key with the control if you so choose), and you're finished, at least with user-interface issues. To make the button functional, you write code in its Click event procedure, as in this fragment:
Private Sub Command1_Click()
' Save data, then unload the current form.
Call SaveDataToDisk
Unload Me
End Sub
You can use two other properties at design time to modify the behavior of a CommandButton control. You can set the Default property to True if it's the default push button for the form (the button that receives a click when the user presses the Enter key—usually the OK or Save button). Similarly, you can set the Cancel property to True if you want to associate the button with the Escape key.
The only relevant CommandButton's run-time property is Value, which sets or returns the state of the control (True if pressed, False otherwise). Value is also the default property for this type of control. In most cases, you don't need to query this property because if you're inside a button's Click event you can be sure that the button is being activated. The Value property is useful only for programmatically clicking a button:
This fires the button's Click event.
Command1.Value = True
The CommandButton control supports the usual set of keyboard and mouse events (KeyDown, KeyPress, KeyUp, MouseDown, MouseMove, MouseUp, but not the DblClick event) and also the GotFocus and LostFocus events, but you'll rarely have to write code in the corresponding event procedures.
CommandButton Controls in VB6
Using CommandButton controls is trivial. In most cases, you just draw the control on the form's surface, set its Caption property to a suitable string (adding an & character to associate a hot key with the control if you so choose), and you're finished, at least with user-interface issues. To make the button functional, you write code in its Click event procedure, as in this fragment:
Private Sub Command1_Click()
' Save data, then unload the current form.
Call SaveDataToDisk
Unload Me
End Sub
You can use two other properties at design time to modify the behavior of a CommandButton control. You can set the Default property to True if it's the default push button for the form (the button that receives a click when the user presses the Enter key—usually the OK or Save button). Similarly, you can set the Cancel property to True if you want to associate the button with the Escape key.
The only relevant CommandButton's run-time property is Value, which sets or returns the state of the control (True if pressed, False otherwise). Value is also the default property for this type of control. In most cases, you don't need to query this property because if you're inside a button's Click event you can be sure that the button is being activated. The Value property is useful only for programmatically clicking a button:
This fires the button's Click event.
Command1.Value = True
The CommandButton control supports the usual set of keyboard and mouse events (KeyDown, KeyPress, KeyUp, MouseDown, MouseMove, MouseUp, but not the DblClick event) and also the GotFocus and LostFocus events, but you'll rarely have to write code in the corresponding event procedures.
Validation Routines for Numbers
Although trapping invalid keys in the KeyPress or KeyDown event procedures seems a great idea at first, when you throw your application to inexperienced users you soon realize that there are many ways for them to enter invalid data. Depending on what you do with this data, your application can come to an abrupt end with a run-time error or—much worse—it can appear to work correctly while it delivers bogus results. What you really need is a bullet-proof method to trap invalid values.
Before I offer you a decent solution to the problem, let me explain why you can't rely solely on trapping invalid keys for your validation chores. What if the user pastes an invalid value from the clipboard? Well, you might say, let's trap the Ctrl+V and Shift+Ins key combinations to prevent the user from doing that! Unfortunately, Visual Basic's TextBox controls offer a default edit menu that lets users perform any clipboard operation by simply right-clicking on them. Fortunately, there's a way around this problem: Instead of trapping a key before it gets to the TextBox control, you trap its effect in the Change event and reject it if it doesn't pass your test. But this makes the structure of the code a little more complex than you might anticipate:
' Form-level variables
Dim saveText As String
Dim saveSelStart As Long
Private Sub Text1_GotFocus()
' Save values when the control gets the focus.
saveText = Text1.Text
saveSelStart = Text1.SelStart
End Sub
Private Sub Text1_Change()
' Avoid nested calls.
Static nestedCall As Boolean
If nestedCall Then Exit Sub
' Test the control's value here.
If IsNumeric(Text1.Text) Then
' If value is OK, save values.
saveText = Text1.Text
saveSelStart = Text1.SelStart
Else
' Prepare to handle a nested call.
nestedCall = True
Text1.Text = saveText
nestedCall = False
Text1.SelStart = saveSelStart
End If
End Sub
Private Sub Text1_KeyUp(KeyCode As Integer, Shift As Integer)
saveSelStart = Text1.SelStart
End Sub
Private Sub Text1_MouseDown(Button As Integer, _
Shift As Integer, X As Single, Y As Single)
saveSelStart = Text1.SelStart
End Sub
Private Sub Text1_MouseMove(Button As Integer, _
Shift As Integer, X As Single, Y As Single)
saveSelStart = Text1.SelStart
End Sub
If the control's value doesn't pass your tests in the Change event procedure, you must restore its previous valid value; this action recursively fires a Change event, and you must prepare yourself to neutralize this nested call. You might wonder why you also need to trap the KeyUp, MouseDown, and MouseMove events: The reason is that you always need to keep track of the last valid position for the insertion point because the end user could move it using arrow keys or the mouse.
The preceding code snippet uses the IsNumeric function to trap invalid data. You should be aware that this function isn't robust enough for most real-world applications. For example, the IsNumeric function incorrectly considers these strings as valid numbers:
123,,,123
345-
$1234 ' What if it isn't a currency field?
2.4E10 ' What if I don't want to support scientific notation?
To cope with this issue, I have prepared an alternative function, which you can modify for your particular purposes. (For instance, you can add support for a currency symbol or the comma as the decimal separator.) Note that this function always returns True when it's passed a null string, so you might need to perform additional tests if the user isn't allowed to leave the field blank:
Function CheckNumeric(text As String, DecValue As Boolean) As Boolean
Dim i As Integer
For i = 1 To Len(text)
Select Case Mid$(text, i, 1)
Case "0" To "9"
Case "-", "+"
' Minus/plus signs are only allowed as leading chars.
If i > 1 Then Exit Function
Case "."
' Exit if decimal values not allowed.
If Not DecValue Then Exit Function
' Only one decimal separator is allowed.
If InStr(text, ".") < i Then Exit Function
Case Else
' Reject all other characters.
Exit Function
End Select
Next
CheckNumeric = True
End Function
If your TextBox controls are expected to contain other types of data, you might be tempted to reuse the same validation framework I showed you previously—including all the code in the GotFocus, Change, KeyUp, MouseDown, and MouseMove event procedures—and replace only the call to IsNumeric with a call to your custom validation routine. Things aren't as simple as they appear at first, however. Say that you have a date field: Can you use the IsDate function to validate it from within the Change event? The answer is, of course, no. In fact, as you enter the first digit of your date value, IsDate returns False and the routine therefore prevents you from entering the remaining characters, and so preventing you from entering any value.
This example explains why a key-level validation isn't always the best answer to your validation needs. For this reason, most Visual Basic programmers prefer to rely on field-level validation and test the values only when the user moves the input focus to another field in the form. I explain field-level validation in the next section.
Before I offer you a decent solution to the problem, let me explain why you can't rely solely on trapping invalid keys for your validation chores. What if the user pastes an invalid value from the clipboard? Well, you might say, let's trap the Ctrl+V and Shift+Ins key combinations to prevent the user from doing that! Unfortunately, Visual Basic's TextBox controls offer a default edit menu that lets users perform any clipboard operation by simply right-clicking on them. Fortunately, there's a way around this problem: Instead of trapping a key before it gets to the TextBox control, you trap its effect in the Change event and reject it if it doesn't pass your test. But this makes the structure of the code a little more complex than you might anticipate:
' Form-level variables
Dim saveText As String
Dim saveSelStart As Long
Private Sub Text1_GotFocus()
' Save values when the control gets the focus.
saveText = Text1.Text
saveSelStart = Text1.SelStart
End Sub
Private Sub Text1_Change()
' Avoid nested calls.
Static nestedCall As Boolean
If nestedCall Then Exit Sub
' Test the control's value here.
If IsNumeric(Text1.Text) Then
' If value is OK, save values.
saveText = Text1.Text
saveSelStart = Text1.SelStart
Else
' Prepare to handle a nested call.
nestedCall = True
Text1.Text = saveText
nestedCall = False
Text1.SelStart = saveSelStart
End If
End Sub
Private Sub Text1_KeyUp(KeyCode As Integer, Shift As Integer)
saveSelStart = Text1.SelStart
End Sub
Private Sub Text1_MouseDown(Button As Integer, _
Shift As Integer, X As Single, Y As Single)
saveSelStart = Text1.SelStart
End Sub
Private Sub Text1_MouseMove(Button As Integer, _
Shift As Integer, X As Single, Y As Single)
saveSelStart = Text1.SelStart
End Sub
If the control's value doesn't pass your tests in the Change event procedure, you must restore its previous valid value; this action recursively fires a Change event, and you must prepare yourself to neutralize this nested call. You might wonder why you also need to trap the KeyUp, MouseDown, and MouseMove events: The reason is that you always need to keep track of the last valid position for the insertion point because the end user could move it using arrow keys or the mouse.
The preceding code snippet uses the IsNumeric function to trap invalid data. You should be aware that this function isn't robust enough for most real-world applications. For example, the IsNumeric function incorrectly considers these strings as valid numbers:
123,,,123
345-
$1234 ' What if it isn't a currency field?
2.4E10 ' What if I don't want to support scientific notation?
To cope with this issue, I have prepared an alternative function, which you can modify for your particular purposes. (For instance, you can add support for a currency symbol or the comma as the decimal separator.) Note that this function always returns True when it's passed a null string, so you might need to perform additional tests if the user isn't allowed to leave the field blank:
Function CheckNumeric(text As String, DecValue As Boolean) As Boolean
Dim i As Integer
For i = 1 To Len(text)
Select Case Mid$(text, i, 1)
Case "0" To "9"
Case "-", "+"
' Minus/plus signs are only allowed as leading chars.
If i > 1 Then Exit Function
Case "."
' Exit if decimal values not allowed.
If Not DecValue Then Exit Function
' Only one decimal separator is allowed.
If InStr(text, ".") < i Then Exit Function
Case Else
' Reject all other characters.
Exit Function
End Select
Next
CheckNumeric = True
End Function
If your TextBox controls are expected to contain other types of data, you might be tempted to reuse the same validation framework I showed you previously—including all the code in the GotFocus, Change, KeyUp, MouseDown, and MouseMove event procedures—and replace only the call to IsNumeric with a call to your custom validation routine. Things aren't as simple as they appear at first, however. Say that you have a date field: Can you use the IsDate function to validate it from within the Change event? The answer is, of course, no. In fact, as you enter the first digit of your date value, IsDate returns False and the routine therefore prevents you from entering the remaining characters, and so preventing you from entering any value.
This example explains why a key-level validation isn't always the best answer to your validation needs. For this reason, most Visual Basic programmers prefer to rely on field-level validation and test the values only when the user moves the input focus to another field in the form. I explain field-level validation in the next section.
Trapping Keyboard Activity - Visual Basic 6 TextBox Control
TextBox controls support KeyDown, KeyPress, and KeyUp standard events. One thing that you will often do is prevent the user from entering invalid keys. A typical example of where this safeguard is needed is a numeric field, for which you need to filter out all nondigit keys:
Private Sub Text1_KeyPress(KeyAscii As Integer)
Select Case KeyAscii
Case Is < 32 ' Control keys are OK.
Case 48 To 57 ' This is a digit.
Case Else ' Reject any other key.
KeyAscii = 0
End Select
End Sub
You should never reject keys whose ANSI code is less than 32, a group that includes important keys such as Backspace, Escape, Tab, and Enter. Also note that a few control keys will make your TextBox beep if it doesn't know what to do with them—for example, a single-line TextBox control doesn't know what to do with an Enter key.
Don't assume that the KeyPress event will trap all control keys under all conditions. For example, the KeyPress event can process the Enter key only if there's no CommandButton control on the form whose Default property is set to True. If the form has a default push button, the effect of pressing the Enter key is clicking on that button. Similarly, no Escape key goes through this event if there's a Cancel button on the form. Finally, the Tab control key is trapped by a KeyPress event only if there isn't any other control on the form whose TabStop property is True.
You can use the KeyDown event procedure to allow users to increase and decrease the current value using Up and Down arrow keys, as you see here:
Private Sub Text1_KeyDown(KeyCode As Integer, Shift As Integer)
Select Case KeyCode
Case vbKeyUp
Text1.Text = CDbl(Text1.Text) + 1
Case vbKeyDown
Text1.Text = CDbl(Text1.Text) -1
End Select
End Sub
There's a bug in the implementation of TextBox ready-only controls. When the Locked property is set to True, the Ctrl+C key combination doesn't correctly copy the selected text to the Clipboard, and you must manually implement this capability by writing code in the KeyPress event procedure
Private Sub Text1_KeyPress(KeyAscii As Integer)
Select Case KeyAscii
Case Is < 32 ' Control keys are OK.
Case 48 To 57 ' This is a digit.
Case Else ' Reject any other key.
KeyAscii = 0
End Select
End Sub
You should never reject keys whose ANSI code is less than 32, a group that includes important keys such as Backspace, Escape, Tab, and Enter. Also note that a few control keys will make your TextBox beep if it doesn't know what to do with them—for example, a single-line TextBox control doesn't know what to do with an Enter key.
Don't assume that the KeyPress event will trap all control keys under all conditions. For example, the KeyPress event can process the Enter key only if there's no CommandButton control on the form whose Default property is set to True. If the form has a default push button, the effect of pressing the Enter key is clicking on that button. Similarly, no Escape key goes through this event if there's a Cancel button on the form. Finally, the Tab control key is trapped by a KeyPress event only if there isn't any other control on the form whose TabStop property is True.
You can use the KeyDown event procedure to allow users to increase and decrease the current value using Up and Down arrow keys, as you see here:
Private Sub Text1_KeyDown(KeyCode As Integer, Shift As Integer)
Select Case KeyCode
Case vbKeyUp
Text1.Text = CDbl(Text1.Text) + 1
Case vbKeyDown
Text1.Text = CDbl(Text1.Text) -1
End Select
End Sub
There's a bug in the implementation of TextBox ready-only controls. When the Locked property is set to True, the Ctrl+C key combination doesn't correctly copy the selected text to the Clipboard, and you must manually implement this capability by writing code in the KeyPress event procedure
example for use OptionButton in Application
The application responds to the following events
The change event of the TextBox reads the value and stores it in a form-level numeric variable.
The click event of optOct button returns curretval in octal.
The click event of the optHex button curerntval in hexadecimal
The click event of the optDec button returns the decimal equivalent of the value held currentval.
The following code is entered in the general declarations section of the Form.
Dim currentval as variant
The variable is initialized to 0 by default. The change event procedure checks to ascertain the number system (Octal, Hexadecimal) that is in effect and then reads in the number.
Private Sub Text1_Change()
If optOct.Value = True Then
currentval = Val ("&O" & LTrim (Text1.Text) & "&")
Elseif optDec.value = True Then
currentval = Val (LTrim (Text1.Text) & "&")
Else
currentval = Val ("&H" & LTrim (Text1.Text) & "&")
End if
End Sub
The Val function is used to translate string to a number and can recognize Octal and Hexadecimal strings. The LTrim function trims the leading blanks in the text. The following code is entered in the click events of the OptionButton controls.
Private Sub optOct_Click()
Text1.Text = Oct(currentval)
End Sub
Private Sub optHex_Click()
Text1.Text = Hex(currentval)
End Sub
Private Sub optDec_Click()
Text1.Text = Format(currentval)
End Sub
The follwoing code is entered in the click event of teh Close button.
Private Sub cmdClose_Click()
Unlod Me
End Sub
The Application is run by pressing F5 or clicking on the Run icon in the tool bar. By pressing the Exit button the program is terminated.
The change event of the TextBox reads the value and stores it in a form-level numeric variable.
The click event of optOct button returns curretval in octal.
The click event of the optHex button curerntval in hexadecimal
The click event of the optDec button returns the decimal equivalent of the value held currentval.
The following code is entered in the general declarations section of the Form.
Dim currentval as variant
The variable is initialized to 0 by default. The change event procedure checks to ascertain the number system (Octal, Hexadecimal) that is in effect and then reads in the number.
Private Sub Text1_Change()
If optOct.Value = True Then
currentval = Val ("&O" & LTrim (Text1.Text) & "&")
Elseif optDec.value = True Then
currentval = Val (LTrim (Text1.Text) & "&")
Else
currentval = Val ("&H" & LTrim (Text1.Text) & "&")
End if
End Sub
The Val function is used to translate string to a number and can recognize Octal and Hexadecimal strings. The LTrim function trims the leading blanks in the text. The following code is entered in the click events of the OptionButton controls.
Private Sub optOct_Click()
Text1.Text = Oct(currentval)
End Sub
Private Sub optHex_Click()
Text1.Text = Hex(currentval)
End Sub
Private Sub optDec_Click()
Text1.Text = Format(currentval)
End Sub
The follwoing code is entered in the click event of teh Close button.
Private Sub cmdClose_Click()
Unlod Me
End Sub
The Application is run by pressing F5 or clicking on the Run icon in the tool bar. By pressing the Exit button the program is terminated.
Setting properties to a TextBox
Setting properties to a TextBox
Text can be entered into the text box by assigning the necessary string to the text property of the control
If the user needs to display multiple lines of text in a TextBox, set the MultiLine property to True
To customize the scroll bar combination on a TextBox, set the ScrollBars property.
Scroll bars will always appear on the TextBox when it's MultiLine property is set to True and its ScrollBars property is set to anything except None(0)
If you set the MultilIne property to True, you can set the alignment using the Alignment property. The test is left-justified by default. If the MultiLine property is et to False, then setting the Alignment property has no effect.
Run-Time Properties of a TextBox control
The Text property is the one you'll reference most often in code, and conveniently it's the default property for the TextBox control. Three other frequently used properties are these:
The SelStart property sets or returns the position of the blinking caret (the insertion point where the text you type appears). Note that the blinking cursor inside TextBox and other controls is named caret, to distinguish it from the cursor (which is implicitly the mouse cursor). When the caret is at the beginning of the contents of the TextBox control, SelStart returns 0; when it's at the end of the string typed by the user, SelStart returns the value Len(Text). You can modify the SelStart property to programmatically move the caret.
The SelLength property returns the number of characters in the portion of text that has been highlighted by the user, or it returns 0 if there's no highlighted text. You can assign a nonzero value to this property to programmatically select text from code. Interestingly, you can assign to this property a value larger than the current text's length without raising a run-time error.
The SelText property sets or returns the portion of the text that's currently selected, or it returns an empty string if no text is highlighted. Use it to directly retrieve the highlighted text without having to query Text, SelStart, and SelLength properties. What's even more interesting is that you can assign a new value to this property, thus replacing the current selection with your own. If no text is currently selected, your string is simply inserted at the current caret position.
When you want to append text to a TextBox control, you should use the following code (instead of using the concatenation operator) to reduce flickering and improve performance:
Text1.SelStart = Len(Text1.Text)
Text1.SelText = StringToBeAdded
One of the typical operations you could find yourself performing with these properties is selecting the entire contents of a TextBox control. You often do it when the caret enters the field so that the user can quickly override the existing value with a new one, or start editing it by pressing any arrow key:
Private Sub Text1_GotFocus()
Text1.SelStart = 0
' A very high value always does the trick.
Text1.SelLength = 9999
End Sub
Always set the SelStart property first and then the SelLength or SelText properties. When you assign a new value to the SelStart property, the other two are automatically reset to 0 and an empty string respectively, thus overriding your previous settings.
The selected text can be copied to the Clipboard by using SelText:
Clipboard.SelText text, [format]
In the above syntax, text is the text that has to be placed into the Clipboard, and format has three possible values.
1. VbCFLink - conversation information
2. VbCFRTF - Rich Text Format
3. VbCFText - Text
We can get text from the clipboard using the GetText() function this way:
Clipboard.GetText ([format])
Text can be entered into the text box by assigning the necessary string to the text property of the control
If the user needs to display multiple lines of text in a TextBox, set the MultiLine property to True
To customize the scroll bar combination on a TextBox, set the ScrollBars property.
Scroll bars will always appear on the TextBox when it's MultiLine property is set to True and its ScrollBars property is set to anything except None(0)
If you set the MultilIne property to True, you can set the alignment using the Alignment property. The test is left-justified by default. If the MultiLine property is et to False, then setting the Alignment property has no effect.
Run-Time Properties of a TextBox control
The Text property is the one you'll reference most often in code, and conveniently it's the default property for the TextBox control. Three other frequently used properties are these:
The SelStart property sets or returns the position of the blinking caret (the insertion point where the text you type appears). Note that the blinking cursor inside TextBox and other controls is named caret, to distinguish it from the cursor (which is implicitly the mouse cursor). When the caret is at the beginning of the contents of the TextBox control, SelStart returns 0; when it's at the end of the string typed by the user, SelStart returns the value Len(Text). You can modify the SelStart property to programmatically move the caret.
The SelLength property returns the number of characters in the portion of text that has been highlighted by the user, or it returns 0 if there's no highlighted text. You can assign a nonzero value to this property to programmatically select text from code. Interestingly, you can assign to this property a value larger than the current text's length without raising a run-time error.
The SelText property sets or returns the portion of the text that's currently selected, or it returns an empty string if no text is highlighted. Use it to directly retrieve the highlighted text without having to query Text, SelStart, and SelLength properties. What's even more interesting is that you can assign a new value to this property, thus replacing the current selection with your own. If no text is currently selected, your string is simply inserted at the current caret position.
When you want to append text to a TextBox control, you should use the following code (instead of using the concatenation operator) to reduce flickering and improve performance:
Text1.SelStart = Len(Text1.Text)
Text1.SelText = StringToBeAdded
One of the typical operations you could find yourself performing with these properties is selecting the entire contents of a TextBox control. You often do it when the caret enters the field so that the user can quickly override the existing value with a new one, or start editing it by pressing any arrow key:
Private Sub Text1_GotFocus()
Text1.SelStart = 0
' A very high value always does the trick.
Text1.SelLength = 9999
End Sub
Always set the SelStart property first and then the SelLength or SelText properties. When you assign a new value to the SelStart property, the other two are automatically reset to 0 and an empty string respectively, thus overriding your previous settings.
The selected text can be copied to the Clipboard by using SelText:
Clipboard.SelText text, [format]
In the above syntax, text is the text that has to be placed into the Clipboard, and format has three possible values.
1. VbCFLink - conversation information
2. VbCFRTF - Rich Text Format
3. VbCFText - Text
We can get text from the clipboard using the GetText() function this way:
Clipboard.GetText ([format])
Some of the pitfalls of ad hoc management
Everyone does projects. The idea that all it takes to be successful is technical knowledge and lots of intensive hard work leads to unnecessary stress, avoidable rework, unnecessary conflicts and a greater chance of failure.
As fun and exciting as it might be, managing in an ad hoc, seat-of-the-pants, shoot-from-the-hip way is not the most effective way when it comes to managing projects. That is because projects often cannot be planned and carried out entirely from the top of your head. When you experience being overwhelmed, or your outcomes are not as good as they could have been, it may be time for managing in a more structured and thoughtful way.
For example, when you start thinking about moving an office, you probably realize that it can be quite complex. There are many dependencies, such as if you committed to be out of the current space by a certain date, you have to make sure you can go somewhere, ideally to your new space. If the new space is not ready, you have to find another temporary place and/or storage. If you cannot find a mover or schedule phone and other installations, you may need to renegotiate the exit date. If the new space is not entirely ready, you need to carefully plan where and how people will operate. As you can see, there is a lot of complexity in even a simple move. This is a project. Managing it like a project and in the right way will improve your chances for success. Projects require a disciplined yet flexible approach.
Not managing projects the right way leads to unnecessary rework and costs, delays, unsatisfied customers and hostile relationships. Think about the times that you or your customers have been impacted by late delivery of project results or by having to do unnecessary rework or by having yourself and others affected by confusion and chaos that could have been avoided by better project planning and control. Think about the time, effort and money that could have been saved. Think about the relations that were disrupted, in some cases irreparably so. In the unlikely case that you have no personal experience, think about high profile projects like the Challenger space shuttle in which poor project management practices led to loss of life or the “Big Dig” in Boston in which poor project planning, communications or control resulted in huge costs and delivery delays.
Managing projects well increases the probability of success and leads to better results, lower costs, less effort, shorter time, better relationships and the ability to continuously improve performance across multiple projects. At the same time, it is necessary to not over manage. Too much of anything is counter productive. In managing projects, the right balance between discipline and flexibility is best.
Most projects are managed by people who are drafted because they have a combination of being available, have subject matter expertise, and are natural coordinators and/or good communicators. Many of these incidental project managers do a great job despite having had little or no training in project management. That is because much of project management is good common sense and because good project managers and performers combine acts of heroism, the acceptance of delays and other shortfalls, good leadership and management skills and the ability to adapt well in moment to moment project performance.
Imagine how much better they might be with a more solid foundation
source from :http://www.profsr.com/msproject/msproj04.htm
image processing
As fun and exciting as it might be, managing in an ad hoc, seat-of-the-pants, shoot-from-the-hip way is not the most effective way when it comes to managing projects. That is because projects often cannot be planned and carried out entirely from the top of your head. When you experience being overwhelmed, or your outcomes are not as good as they could have been, it may be time for managing in a more structured and thoughtful way.
For example, when you start thinking about moving an office, you probably realize that it can be quite complex. There are many dependencies, such as if you committed to be out of the current space by a certain date, you have to make sure you can go somewhere, ideally to your new space. If the new space is not ready, you have to find another temporary place and/or storage. If you cannot find a mover or schedule phone and other installations, you may need to renegotiate the exit date. If the new space is not entirely ready, you need to carefully plan where and how people will operate. As you can see, there is a lot of complexity in even a simple move. This is a project. Managing it like a project and in the right way will improve your chances for success. Projects require a disciplined yet flexible approach.
Not managing projects the right way leads to unnecessary rework and costs, delays, unsatisfied customers and hostile relationships. Think about the times that you or your customers have been impacted by late delivery of project results or by having to do unnecessary rework or by having yourself and others affected by confusion and chaos that could have been avoided by better project planning and control. Think about the time, effort and money that could have been saved. Think about the relations that were disrupted, in some cases irreparably so. In the unlikely case that you have no personal experience, think about high profile projects like the Challenger space shuttle in which poor project management practices led to loss of life or the “Big Dig” in Boston in which poor project planning, communications or control resulted in huge costs and delivery delays.
Managing projects well increases the probability of success and leads to better results, lower costs, less effort, shorter time, better relationships and the ability to continuously improve performance across multiple projects. At the same time, it is necessary to not over manage. Too much of anything is counter productive. In managing projects, the right balance between discipline and flexibility is best.
Most projects are managed by people who are drafted because they have a combination of being available, have subject matter expertise, and are natural coordinators and/or good communicators. Many of these incidental project managers do a great job despite having had little or no training in project management. That is because much of project management is good common sense and because good project managers and performers combine acts of heroism, the acceptance of delays and other shortfalls, good leadership and management skills and the ability to adapt well in moment to moment project performance.
Imagine how much better they might be with a more solid foundation
source from :http://www.profsr.com/msproject/msproj04.htm
image processing
Projects, Their Outcomes and Project Management
Projects are efforts to achieve objectives, within finite time and cost expectations. Projects are contrasted with operational activities – the repetitive things performed regularly over time. In some way the dividing line between projects and operational activities is not clear; often an operational activity is a series of small projects. However, what is clear is, healthy projects have a finite end that is reached either when the project objectives have been met or when the project is cancelled.
In this paper the term outcome will be used to mean any project result, whether it is a new or changed product, event or process. Projects produce outcomes like newly design car models, an annual budget, a great party, or a new procedure. The use of the outcome and its value after the project delivers it are the underlying justification for the project.
So, what does it mean to manage a project? It is the application of a broad set of skills to properly initiate, plan, execute, control and close a project. The primary skills are scoping (i.e., describing and agreeing on project objectives and requirements), scheduling, and estimating. Added to these core skills are managing risk and uncertainty, managing quality, communicating, managing ourselves, and collaborating with others, including suppliers of goods and services and everyone else who works on or is affected by the project. The people who are involved or interested in a project are referred to as stakeholders.
To put projects and project management into practical context, it is useful to take a systems view. This view recognizes that everything is operating in a system of interacting people, organizations, things and processes. Change or activity anywhere can have an effect elsewhere. The more one can predict the effect, the greater one's control of the system's performance. In complex systems, no one can ever predict the effect of actions with 100% accuracy. A project is a complex system. Project management itself is also a complex system.
Figure 1, below, is a picture of project management as a system. The Unified Project Management Methodology (UPMM™) is one of many views in use today to describe the various activities in managing projects.
A single project is managed from Originating, the time someone communicates an idea that may someday become a project, through Closing, the completion of the project, if in fact the project becomes a project and is completed.
Surrounding the performance of a single project are activities that support and direct the organization and its ability to perform multiple projects in a complex, changing environment. These activities include Ongoing Improvement, the effort to learn from past experience and improve the way you perform and manage projects; Portfolio Management & Governance, the decision making needed to select, initiate and continue the right projects and to manage the optimum use of scarce resources; and Multi-project Management, the process for looking across all of the projects being performed and managing them as a group to avoid conflicts and promote synergy.
Effective portfolio management and multi-project management are among the most critical factors for successful projects. They address many of the root causes of chronic problems in projects, such as the chronic over burdening of resources and constant priority shifts that create confusion and impact productivity.
Collaboration and Consulting represents the critical need for teamwork, communication, coordination and the management of knowledge and information.
In this paper the term outcome will be used to mean any project result, whether it is a new or changed product, event or process. Projects produce outcomes like newly design car models, an annual budget, a great party, or a new procedure. The use of the outcome and its value after the project delivers it are the underlying justification for the project.
So, what does it mean to manage a project? It is the application of a broad set of skills to properly initiate, plan, execute, control and close a project. The primary skills are scoping (i.e., describing and agreeing on project objectives and requirements), scheduling, and estimating. Added to these core skills are managing risk and uncertainty, managing quality, communicating, managing ourselves, and collaborating with others, including suppliers of goods and services and everyone else who works on or is affected by the project. The people who are involved or interested in a project are referred to as stakeholders.
To put projects and project management into practical context, it is useful to take a systems view. This view recognizes that everything is operating in a system of interacting people, organizations, things and processes. Change or activity anywhere can have an effect elsewhere. The more one can predict the effect, the greater one's control of the system's performance. In complex systems, no one can ever predict the effect of actions with 100% accuracy. A project is a complex system. Project management itself is also a complex system.
Figure 1, below, is a picture of project management as a system. The Unified Project Management Methodology (UPMM™) is one of many views in use today to describe the various activities in managing projects.
A single project is managed from Originating, the time someone communicates an idea that may someday become a project, through Closing, the completion of the project, if in fact the project becomes a project and is completed.
Surrounding the performance of a single project are activities that support and direct the organization and its ability to perform multiple projects in a complex, changing environment. These activities include Ongoing Improvement, the effort to learn from past experience and improve the way you perform and manage projects; Portfolio Management & Governance, the decision making needed to select, initiate and continue the right projects and to manage the optimum use of scarce resources; and Multi-project Management, the process for looking across all of the projects being performed and managing them as a group to avoid conflicts and promote synergy.
Effective portfolio management and multi-project management are among the most critical factors for successful projects. They address many of the root causes of chronic problems in projects, such as the chronic over burdening of resources and constant priority shifts that create confusion and impact productivity.
Collaboration and Consulting represents the critical need for teamwork, communication, coordination and the management of knowledge and information.
Friday, August 21, 2009
Where to get the funs descriptions from
This topics won't tell how to change the button text through API or how to find a file quickly. It is not a API functions documentation.
To get the description of an API function, you need to have either SDK help file or the Microsoft SDK documentation (it's more that 40MB I think - how can I place it here?). Such SDK helps are shipped with Borland Delphi 3.0 package or MS Visual C++ 5.0 for example. Search the Internet and ask your friends to get one. The newer it is the better.
Note that SDK help for Win 3.x won't help you as some functions are obsolete, though most of them still exist for compatibility in Win95.
To get the description of an API function, you need to have either SDK help file or the Microsoft SDK documentation (it's more that 40MB I think - how can I place it here?). Such SDK helps are shipped with Borland Delphi 3.0 package or MS Visual C++ 5.0 for example. Search the Internet and ask your friends to get one. The newer it is the better.
Note that SDK help for Win 3.x won't help you as some functions are obsolete, though most of them still exist for compatibility in Win95.
API : Some Windows Specifics
This topic is intended to give you a clue about some Windows specifics that are not the same under VB.
Windows identifies every form, control, menu, menu item or whatever you can think of by its handle. When your application is run, every control on it is assigned a handle which is used later to separate the button from the rest of the controls. If you want to perform any operation on the button through an API you must use this handle. Where to get it from? Well VB has provided a Hwnd property for all controls that have handles in Windows.
Windows works with pixels, not twips. So, it is a good idea to have the controls you'll use API functions over set their ScaleMode properties to Pixel(3) so that you can use ScaleXXX properties to get their metrics. But even though, you have this opportunity, you may still need to convert twips to pixels and vice versa. You do it using TwipsPerPixelX and TwipsPerPixelY or the global Screen object. Here it is:
pixXValue = twipXValue \ Screen.TwipsPerPixelX
pixYValue = twipYValue \ Screen.TwipsPerPixelY
twipXValue = pixXValue * Screen.TwipsPerPixelX
twipYValue = pixYValue * Screen.TwipsPerPixelY
I haven't really seen the TwipsPerPixelX and TwipsPerPixelY value to be different, but its always better to make difference, at least for the good programing style. Also note that \ (for integer division) is used instead of / as pixels must always be whole numbers.
Another thing to mention is that Windows uses different coordinate systems for the functions. So, be careful.
And lastly, don't forget that VB is safe till the moment you begin to use APIs. A single syntax error in an API call may cause VB to crash (save often!). Also VB cannot debug APIs and if your program is crashing or behaving awkwardly, firstly check the API calls - for missed ByVal, for mistaken type or parameter, everything).
Windows identifies every form, control, menu, menu item or whatever you can think of by its handle. When your application is run, every control on it is assigned a handle which is used later to separate the button from the rest of the controls. If you want to perform any operation on the button through an API you must use this handle. Where to get it from? Well VB has provided a Hwnd property for all controls that have handles in Windows.
Windows works with pixels, not twips. So, it is a good idea to have the controls you'll use API functions over set their ScaleMode properties to Pixel(3) so that you can use ScaleXXX properties to get their metrics. But even though, you have this opportunity, you may still need to convert twips to pixels and vice versa. You do it using TwipsPerPixelX and TwipsPerPixelY or the global Screen object. Here it is:
pixXValue = twipXValue \ Screen.TwipsPerPixelX
pixYValue = twipYValue \ Screen.TwipsPerPixelY
twipXValue = pixXValue * Screen.TwipsPerPixelX
twipYValue = pixYValue * Screen.TwipsPerPixelY
I haven't really seen the TwipsPerPixelX and TwipsPerPixelY value to be different, but its always better to make difference, at least for the good programing style. Also note that \ (for integer division) is used instead of / as pixels must always be whole numbers.
Another thing to mention is that Windows uses different coordinate systems for the functions. So, be careful.
And lastly, don't forget that VB is safe till the moment you begin to use APIs. A single syntax error in an API call may cause VB to crash (save often!). Also VB cannot debug APIs and if your program is crashing or behaving awkwardly, firstly check the API calls - for missed ByVal, for mistaken type or parameter, everything).
Windows API Message
OK, now you know what API function is, but you have definitely heart of messages (if you haven't you will soon do) and wonder what this is.
Messages are the basic way Windows tells your program that some kind of input has occurred and you must process it. A message to your form is sent when the user clicks on a button, moves the mouse over it or types text in a textbox.
All messages are sent along with four parameters - a window handle, a message identifier and two 32-bit (Long) values. The window handle contains the handle of the window the message is going to. The identifier is actually the type of input occurred (click, mousemove) and the two value specify an additional information for the message (like where is the mouse cursor when the mouse is been moved).
But, when messages are sent to you, why don't you see them, looks like someone is stealing your mail. And before you get angry enough, let me tell you.
The theft is actually VB. But he does not steal your mail, but instead read it for you and give you just the most important in a better look (with some information hidden from time to time). This better look is the events you write code for.
So, when the user moves the mouse over your form, Windows sends WM_MOUSEMOVE to your window, VB get the message and its parameters and executes the code you've entered for Button_MouseMove event. Along the way, VB has transformed the second 32-bit value of the message (it contains the x and y position in pixels, 16-bit each) into two Single type value of twips.
Now, say you need the coordinates of the mouse in pixels. VB converted them into twips, and now you will convert them into pixels again. Apart from losing time, it is somehow irritating to know Windows gives you what you need and VB "favorably" alters it so that you must re-alter it. Here you will ask - Can't I receive the messages myself. OK, there is a way called SubClassing, but you should use it only if really necessary as it goes a bit against the concepts of safe programming of VB.
Something else that needs to be said: You can send massages to your own window or to another one yourself. You just call SendMessage or PostMessage (SendMessage will cause the window to process the message immediately and Post message will post it onto a queue, called message queue, after any other messages waiting to be processed (it will return after the message is processed, i.e. with some delay)). You must specify the window handle to send the message to, the message identifier (all message identifiers are available as constants in VB API Text Viewer) and the two 32-bit values.
Messages are the basic way Windows tells your program that some kind of input has occurred and you must process it. A message to your form is sent when the user clicks on a button, moves the mouse over it or types text in a textbox.
All messages are sent along with four parameters - a window handle, a message identifier and two 32-bit (Long) values. The window handle contains the handle of the window the message is going to. The identifier is actually the type of input occurred (click, mousemove) and the two value specify an additional information for the message (like where is the mouse cursor when the mouse is been moved).
But, when messages are sent to you, why don't you see them, looks like someone is stealing your mail. And before you get angry enough, let me tell you.
The theft is actually VB. But he does not steal your mail, but instead read it for you and give you just the most important in a better look (with some information hidden from time to time). This better look is the events you write code for.
So, when the user moves the mouse over your form, Windows sends WM_MOUSEMOVE to your window, VB get the message and its parameters and executes the code you've entered for Button_MouseMove event. Along the way, VB has transformed the second 32-bit value of the message (it contains the x and y position in pixels, 16-bit each) into two Single type value of twips.
Now, say you need the coordinates of the mouse in pixels. VB converted them into twips, and now you will convert them into pixels again. Apart from losing time, it is somehow irritating to know Windows gives you what you need and VB "favorably" alters it so that you must re-alter it. Here you will ask - Can't I receive the messages myself. OK, there is a way called SubClassing, but you should use it only if really necessary as it goes a bit against the concepts of safe programming of VB.
Something else that needs to be said: You can send massages to your own window or to another one yourself. You just call SendMessage or PostMessage (SendMessage will cause the window to process the message immediately and Post message will post it onto a queue, called message queue, after any other messages waiting to be processed (it will return after the message is processed, i.e. with some delay)). You must specify the window handle to send the message to, the message identifier (all message identifiers are available as constants in VB API Text Viewer) and the two 32-bit values.
API Declaration
As said in What's API, functions are declared in Dlls located in the Windows System directory. You can type in the declaration of an API just as you do with any other function exported from a Dll, but VB has provided an easier way to do it. It is called API Text Viewer.
To have some API declared in your project, just launch API Text Viewer, open Win32Api.txt (or .MDB if you have converted it into a database to speed it up), choose Declares, find the function, click Add and then Copy. Go to your project and paste it in. Do the same to have a predefined constant or type.
There are few problems you may face:
Suppose you want to declare a function in your form module. You paste the declaration and run the program. VB says Compile Error, ...and Declare statements not allowed as Public members of ... . Sounds bad, but it isn't, all you need to do is add Private in front of the declaration (like Private Declare Function ...). Do not forget, though, that the function will be visible only within this form module.
In some cases, you may get the message Ambiguous name detected by VB. It means you have two functions, constants or whatsoever sharing one name. As most of the functions (maybe all of them, I haven't checked that) are aliased, which means they are given different names, and not their original using Alias clause, you may simply change the name of the function and it will still work.
You may read the Declare statement help topic of VB's for description of Alias.
To have some API declared in your project, just launch API Text Viewer, open Win32Api.txt (or .MDB if you have converted it into a database to speed it up), choose Declares, find the function, click Add and then Copy. Go to your project and paste it in. Do the same to have a predefined constant or type.
There are few problems you may face:
Suppose you want to declare a function in your form module. You paste the declaration and run the program. VB says Compile Error, ...and Declare statements not allowed as Public members of ... . Sounds bad, but it isn't, all you need to do is add Private in front of the declaration (like Private Declare Function ...). Do not forget, though, that the function will be visible only within this form module.
In some cases, you may get the message Ambiguous name detected by VB. It means you have two functions, constants or whatsoever sharing one name. As most of the functions (maybe all of them, I haven't checked that) are aliased, which means they are given different names, and not their original using Alias clause, you may simply change the name of the function and it will still work.
You may read the Declare statement help topic of VB's for description of Alias.
C# Primary Sites
C# Primary Sites
The Code Project Whitepapers and code examples by category. Good code resource.Visual C# KicksDeveloperFusion (C# Directory: U.K. Developer Community) C# CornerC# developers network: code, downloads, discussions,... C# HelpHelp for C# Developers Creating Designable Components for Microsoft Visual Studio .NET DesignersAn introduction to using components in C# development. (July 2000 by Shawn Burke, Microsoft Corp.) C# Station DevX Resources C# Friends See whitepapers, a class- "browser" reference, and more... by Salman Ahmed. Lutz Roeder's Programming .NETTools and source code examples. Reflector assembly browser, Resourcer, Digger. Also applications and source code. Code Hound C# Search Engine C# Notebook Notebooks, Bookstore, Code, .dll tutorial,..much more CSharpHelp.Com The place for C# developers. Peter Drayton's .NET GoodiesC# Utilities & samples with code.
The Code Project Whitepapers and code examples by category. Good code resource.Visual C# KicksDeveloperFusion (C# Directory: U.K. Developer Community) C# CornerC# developers network: code, downloads, discussions,... C# HelpHelp for C# Developers Creating Designable Components for Microsoft Visual Studio .NET DesignersAn introduction to using components in C# development. (July 2000 by Shawn Burke, Microsoft Corp.) C# Station DevX Resources C# Friends See whitepapers, a class- "browser" reference, and more... by Salman Ahmed. Lutz Roeder's Programming .NETTools and source code examples. Reflector assembly browser, Resourcer, Digger. Also applications and source code. Code Hound C# Search Engine C# Notebook Notebooks, Bookstore, Code, .dll tutorial,..much more CSharpHelp.Com The place for C# developers. Peter Drayton's .NET GoodiesC# Utilities & samples with code.
Thursday, August 20, 2009
Graphically Show CPU Memory Usage no of process
This is simple program that shows how to use performance calculator to get % CPU usage, memory usage in kb and number of processes running on the computer. You can modify the code for your convenience. Do reply me.
Downloads Hear
Downloads Hear
Monday, August 17, 2009
Visual Basic application and create a full fledged screen saver
Visual Basic is a great developers language it allows you to create applications that are very functional and to do so in a quick way. This is why people love VB6. However, at times it can be hard to figure out how to interact directly with the Windows Operating System. To do this we need to make API calls. Anyone who has delved into using VB and API's knows that it can be a little cumbersome at times. However, this tutorial demonstrates how you can make the API calls from your Visual Basic application and create a full fledged screen saver!
A screen saver at its core is very simple. It is simply a window that covers the entire screen. In Visual Basic 6 this is accomplished by createing a form that will be displayed full size overtop of everything else. Lets start with the simple. Create a new VB6 project with just the main form. Set the properties to the following:
Property Setting
Caption ""
ControlBox False
MinButton False
MaxButton False
BorderStyle 0 - None
WindowState 2 - Maximized
BackColor &H0
Private Declare Function SetWindowPos Lib "user32" _
(ByVal hwnd As Long, ByVal hWndInsertAfter As Long, _
ByVal x As Long, ByVal Y As Long, ByVal cx As Long, _
ByVal cy As Long, ByVal wFlags As Long) As Long
Private Declare Function ShowCursor Lib "user32" _
(ByVal bShow As Long) As Long
We are going to use these functions a little later. First lets create a helper subroutine that will always keep our form on top.
Sub AlwaysOnTop (FrmID As Form, OnTop As Boolean)
Const SWP_NOMOVE = 2
Const SWP_NOSIZE = 1
Const FLAGS = SWP_NOMOVE Or SWP_NOSIZE
Const HWND_TOPMOST = -1
Const HWND_NOTOPMOST = -2
If OnTop Then
OnTop = SetWindowPos(FrmID.hWnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS)
Else
OnTop = SetWindowPos(FrmID.hWnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS)
End If
End Sub
The next part is the load-up of our Screen Saver: put these lines in the Load event of the form. This will handle things when the Windows OS launches our screen saver.
Select Case LCase(Left(Command, 2))
Case "/p": End
Case "/s"
Case Else: Me.Hide: frmSettings.Show: Exit Sub
End Select
Dim x As Integer
Call AlwaysOnTop(Me, True)
x = ShowCursor(False)
The form will always stay on top and the cursor will desappear.
When the Screen Saver unloads, we must do the inverse. Put these lines in the Unload event of the form.
Dim x As Integer
x = ShowCursor(True)
The first 5 lines of the Form_Load event are needed to make the Screen Saver work, work as an example or show its settings. Windows tells the Screen Saver what to do through command line parameters: /S tells the Screen Saver to start working, /P tells the Screen Saver to start working in a preview area, and no parameters makes the Screen Saver show its settings dialog. So, you may create a form called frmSettings that gives the opportunity to set Screen Saver parameters and to save them in a INI file or in the Registry; that dialog must unload the program when it is finished.
Another important thing to do, is to handle the events that unload the Screen Saver. A Screen Saver is usually unloaded when we move the mouse or hit a key, so we'll put the instruction Unload Me in the KeyPress event of the form. For the MouseMove or MouseClick events, use these lines:
Static Count As Integer
Count = Count + 1
If Count > 5 Then
Unload Me
End If
This makes sure that the mouse is moved atleast a little bit before it exits. Otherwise your screen saver will exit too easily (with just a bump of the desk or something).
Well, it is your turn now! Can you creat an original and good Screen Saver. You can use controls (even OCXs) to create the graphic, and add code anywhere you want. If you want, you can download this example, located in the samples section of the site, demostrating a full working Screen Saver.
Installing The Screen Saver
When you have finished creating the look of the Screen Saver, it's the moment to compile it and bring it to life. Once you have compiled your Screen Saver, change its EXE extension to SCR. Then, copy it to the Windows\System folder.
To use the Screen Saver, go in the Control Panel, double-click the icon Screen, select the second tab (Screen Saver) and select your program from the Screen Saver dropdown list. Then, click OK.
With these properties, the form will be black, will have no border, buttons or title bar and will cover all the screen.
So, create a form and give it the above properties.
Now we must do two other things. First, each screen saver is a form that stays on the top of all others. Second, we notice that, during the display of a Screen Saver, the mouse cursor desappear.
To make our program do these two things, we first put these two lines in the declarations section of the form:
from http://www.vb6.us/tutorials/createing-visual-basic-screen-saver
A screen saver at its core is very simple. It is simply a window that covers the entire screen. In Visual Basic 6 this is accomplished by createing a form that will be displayed full size overtop of everything else. Lets start with the simple. Create a new VB6 project with just the main form. Set the properties to the following:
Property Setting
Caption ""
ControlBox False
MinButton False
MaxButton False
BorderStyle 0 - None
WindowState 2 - Maximized
BackColor &H0
Private Declare Function SetWindowPos Lib "user32" _
(ByVal hwnd As Long, ByVal hWndInsertAfter As Long, _
ByVal x As Long, ByVal Y As Long, ByVal cx As Long, _
ByVal cy As Long, ByVal wFlags As Long) As Long
Private Declare Function ShowCursor Lib "user32" _
(ByVal bShow As Long) As Long
We are going to use these functions a little later. First lets create a helper subroutine that will always keep our form on top.
Sub AlwaysOnTop (FrmID As Form, OnTop As Boolean)
Const SWP_NOMOVE = 2
Const SWP_NOSIZE = 1
Const FLAGS = SWP_NOMOVE Or SWP_NOSIZE
Const HWND_TOPMOST = -1
Const HWND_NOTOPMOST = -2
If OnTop Then
OnTop = SetWindowPos(FrmID.hWnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS)
Else
OnTop = SetWindowPos(FrmID.hWnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS)
End If
End Sub
The next part is the load-up of our Screen Saver: put these lines in the Load event of the form. This will handle things when the Windows OS launches our screen saver.
Select Case LCase(Left(Command, 2))
Case "/p": End
Case "/s"
Case Else: Me.Hide: frmSettings.Show: Exit Sub
End Select
Dim x As Integer
Call AlwaysOnTop(Me, True)
x = ShowCursor(False)
The form will always stay on top and the cursor will desappear.
When the Screen Saver unloads, we must do the inverse. Put these lines in the Unload event of the form.
Dim x As Integer
x = ShowCursor(True)
The first 5 lines of the Form_Load event are needed to make the Screen Saver work, work as an example or show its settings. Windows tells the Screen Saver what to do through command line parameters: /S tells the Screen Saver to start working, /P tells the Screen Saver to start working in a preview area, and no parameters makes the Screen Saver show its settings dialog. So, you may create a form called frmSettings that gives the opportunity to set Screen Saver parameters and to save them in a INI file or in the Registry; that dialog must unload the program when it is finished.
Another important thing to do, is to handle the events that unload the Screen Saver. A Screen Saver is usually unloaded when we move the mouse or hit a key, so we'll put the instruction Unload Me in the KeyPress event of the form. For the MouseMove or MouseClick events, use these lines:
Static Count As Integer
Count = Count + 1
If Count > 5 Then
Unload Me
End If
This makes sure that the mouse is moved atleast a little bit before it exits. Otherwise your screen saver will exit too easily (with just a bump of the desk or something).
Well, it is your turn now! Can you creat an original and good Screen Saver. You can use controls (even OCXs) to create the graphic, and add code anywhere you want. If you want, you can download this example, located in the samples section of the site, demostrating a full working Screen Saver.
Installing The Screen Saver
When you have finished creating the look of the Screen Saver, it's the moment to compile it and bring it to life. Once you have compiled your Screen Saver, change its EXE extension to SCR. Then, copy it to the Windows\System folder.
To use the Screen Saver, go in the Control Panel, double-click the icon Screen, select the second tab (Screen Saver) and select your program from the Screen Saver dropdown list. Then, click OK.
With these properties, the form will be black, will have no border, buttons or title bar and will cover all the screen.
So, create a form and give it the above properties.
Now we must do two other things. First, each screen saver is a form that stays on the top of all others. Second, we notice that, during the display of a Screen Saver, the mouse cursor desappear.
To make our program do these two things, we first put these two lines in the declarations section of the form:
from http://www.vb6.us/tutorials/createing-visual-basic-screen-saver
Tuesday, August 4, 2009
Working with arrays ListBox
An array can also be assigned to a variable in code. Look at the following example and understand that that is not an implicit declaration. The variable "Week" is declared as Variant. It is assigned an array value in code.
Now, when we get to the next set of controls, different kinds of Lists, these notions may prove useful.
ListBox
With the ListBox control the user can select items from a list of choices. Although the list of choices can be entered in the List property of the control, as in the example below, this is not a very good habit to get into. It is essentially "hardcoding" data into the program and it can cause maintenance headaches.
Now, when we get to the next set of controls, different kinds of Lists, these notions may prove useful.
ListBox
With the ListBox control the user can select items from a list of choices. Although the list of choices can be entered in the List property of the control, as in the example below, this is not a very good habit to get into. It is essentially "hardcoding" data into the program and it can cause maintenance headaches.
Working with arrays
Before we get to today's lesson on common controls, we will cover a bit of programming theory on Arrays.
In VB, arrays work in much the same way as they do in all other languages you have studied. By definition an array is an indexed variable, meaning it is one variable with many parts, each part being referenced by an index number. The index number being numeric, it can be manipulated by loop statements, incremented, decremented, etc. An array can contain any valid data type and, if it is of the Variant type, can even contain elements of different types.
An array is declared like any other variable, with the addition of an index:
Dim Department(6) As String
will declare an array of 7 elements of the String type (we assume that it will be 7 Department names). The only problem with this declaration is that the index goes from 0 to 6. So, if you want the name of the sixth Department you have to specify Department(5), which can be confusing at times.
To work around this problem you can specify the starting index in the declaration:
Dim Months(1 To 12) As String
Thus, Months(1) is January and Months(12) is December.
You don't even have to start at 1. If your Sections are numbered 101 - 120 you can define an array:
Dim Sections(101 To 120) As Integer
One common method of manipulating arrays is to use For...Next loops:
In VB, arrays work in much the same way as they do in all other languages you have studied. By definition an array is an indexed variable, meaning it is one variable with many parts, each part being referenced by an index number. The index number being numeric, it can be manipulated by loop statements, incremented, decremented, etc. An array can contain any valid data type and, if it is of the Variant type, can even contain elements of different types.
An array is declared like any other variable, with the addition of an index:
Dim Department(6) As String
will declare an array of 7 elements of the String type (we assume that it will be 7 Department names). The only problem with this declaration is that the index goes from 0 to 6. So, if you want the name of the sixth Department you have to specify Department(5), which can be confusing at times.
To work around this problem you can specify the starting index in the declaration:
Dim Months(1 To 12) As String
Thus, Months(1) is January and Months(12) is December.
You don't even have to start at 1. If your Sections are numbered 101 - 120 you can define an array:
Dim Sections(101 To 120) As Integer
One common method of manipulating arrays is to use For...Next loops:
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