Wednesday, 6 July 2011

Common Dialog Control

In Windows operating system, we often see a set of commonly used dialog boxes, such as Open dialog box. For example, when you choose File -> Open of WordPad or File->Open of Notepad, you see the same dialog box with the same interface. This is so because all these applications make use of common dialog boxes developed by Microsoft. That means we can use all these common dialog boxes without having to create these dialog boxes from scratch. That not only saves a lot of time, it also allows you to provide standard interface to users.

Now let us understand how to use these common dialog boxes in Visual Basic.

Common Dialog Control
Visual Basic allows your application to use common dialog boxes trough an ActiveX control called “Common Dialog Control”. This is not a standard control that you find in toolbox by default. Instead you have to load this control into your project.

What is an ActiveX Control?
For the time being it will suffice to know that an ActiveX control is a control that is not part of intrinsic controls that you find in Toolbox. And an ActiveX control is a user-defined control developed using ActiveX technology. These controls come in the form of .OCX file. Each .OCX file may contain one or more ActiveX controls. Each control is assigned a particular task. There are hundreds of ActiveX controls in the market today. And surely more will come in future. It is also possible for a Visual Basic programmer to create his own ActiveX control and distribute to other developers (who may use any tools that is supporting ActiveX).

Note: If you want to use an ActiveX control, first you must install ActiveX control in question properly and then load it into Visual Basic project. When you install Visual Basic, it installs good number of ActiveX controls into your machine. So all that you have to do is load them into your project and start using them.

Note: We will discuss more about ActiveX technology and how to create our own ActiveX control in chapter 27,28 and 29.

How to load an ActiveX control into Visual Basic project?
The following procedure is to be followed to load an ActiveX control into a Visual Basic project.

1. Select Project -> Components in Visual Basic IDE
Visual Basic displays a window that contains the list of ActiveX controls that are installed in your machine.
2. Make sure Control tab is selected.
3. Go to the control that you want to load. In this case we want to load Microsoft Common Dialog Control 6.0, so select that control.
4. Turn on the checkbox on the left of the control.
At this stage, the name and path of the selected .OCX file will be displayed at the bottom of Component dialog.
5. Click on Ok button.
Once an ActiveX control is loaded, one or more icons are displayed depending upon whether the selected component contains one or more controls.

What does Common dialog control have?
Microsoft common dialog control allows you to access a set of dialog boxes through its methods and properties.

The following are the dialog boxes that can be accessed through Common dialog control.

Dialog box Meaning Method to Invoke
Open Displays the list of files and directories and allows you to select a file. ShowOpen
Save As Displays the list of files and directories and allows you to select a file. ShowSave
Color Displays a list of standard colors and System colors. ShowColor
Font Displays a dialog box with the list of available fonts and styles. ShowFont
Print Displays print dialog box ShowPrinter
Help Invokes help window using the given file. ShowHelp
Table 9.1: Dialog boxes that can be accessed through common dialog control.

Now, let us understand properties related to each of these common dialog boxes.

Open and Save As dialog boxes
Open dialog box is used to let user select a file. It contains list of files, directories and also a text box into which you can enter filename.

Save As dialog box is same as Open dialog box except the caption. Both the dialog boxes display list of files, directories and drives so that user can select a file from anywhere from the file system.

The following are the properties that are related to Open and Save As dialog boxes.

Property Meaning
CancelError Specifies whether a trappable runtime error (with number 32755) occurs when user selected Cancel button or no error occurs.
DefaultExt Specifies the default extension, such as .txt or .frm for files. When a file with no extension is entered the default extension is automatically added.
DialogTitle Contains the title of the dialog box. This is ignored for Font, Color and Print dialog boxes.
FileTitle Returns only the filename without path.
Filter Specifies the filters to be displayed in Type list box of dialog.
FilterIndex Specifies the default filter.
InitDir Specifies the directory to be used initially. If not specified then current directory is used.
FileName Returns the path and filename of the selected file.
Table 9.2: Properties that are specific to Open and Save As dialog boxes.

The following code listing shows you how to use Open dialog box.

‘ Open button displays Open dialog box and takes the filename
Private Sub CmdOpen_Click()

With CommonDialog1
‘ set two filters; one is *.txt another is *.*
.Filter = "Text Files|*.txt|All files|*.*"
.FilterIndex = 0 ' first filter is default
.DialogTitle = "Select a text file"
‘ invoke Open dialog box
.ShowOpen
' print filename on the form
Print .FileName
End With
End sub
Listing 9.1: Displaying Open dialog box to take a filename from user.

If you run the above code, you will see a dialog box

Font Dialog box
Font dialog box displays the list of available font names and other font styles. This dialog box can display the fonts supported by either Printer or Screen or Both.

Note: You must specify whether you want to list fonts supported by Screen or Printer or Both. Unless you specify this, no fonts will be displayed in Font dialog box.

The following are the properties related to Font dialog box.

Property Meaning
FontBold Whether bold was selected
FontItalic Whether italic was selected.
FontStrikethru Whether strikethrough was selected.
FontUnderline Whether underline was selected.
FontName The selected font name
FontSize The selected font size.
Table 9.3: Properties that are specific to Font dialog box.

Flags property for Font Dialog box
This property is used to set options related to Font dialog box. You can set more than one flag using OR operator.

The following is the list of flags related to Font dialog box.

Flag Constant Value Meaning
CdlCFBoth &H3 Causes fonts supported by Screen and Printer to be listed.
CdlCFEffects &H100 Causes the dialog box to display Underline and Strikethrough effects also.
CdlCFPrintersFonts &H2 Causes only fonts supported by printer to be listed.
CdlCFScreenFonts &H1 Causes only fonts supported by screen to be listed.
Table 9.4: Flags related to Font dialog box

Please see on-line documentation for complete list of flags.

The following listing illustrates how to use Font dialog box to allow user to select Font related options and set those options to current form.
Private Sub cmdFont_Click()

With CommonDialog1
'Display screen fonts with effects
.Flags = cdlCFScreenFonts Or cdlCFEffects
.ShowFont
Me.FontName = .FontName
Me.FontSize = .FontSize
Me.FontBold = .FontBold
Me.FontItalic = .FontItalic
Me.FontUnderline = .FontUnderline
Me.FontStrikethru = .FontStrikethru
Print "This is sample text"
End With
End Sub
Listing 9.2: Displaying Font dialog box.

Color Dialog box
Color dialog box displays color palette from which user can select a color. Color dialog box also allows users to create a custom color and select it.

Color property returns the selected color. Flags property can be used to specify whether user should be allowed to define custom colors (cdlCGPreventFullOpen) and whether full dialog box (including Define custom colors section) is to be displayed.

The following code displays Color dialog box and changes the background of the form with the color selected by user.

Private Sub cmdBKColor_Click()
With CommonDialog1
.Flags = cdlCCFullOpen
.ShowColor
Me.BackColor = .Color
End With
End Sub
Listing 9.3: Invoking Color dialog box.

Color dialog box with Define custom color section open.

Print Dialog Box
The Print dialog box allows the user to specify how output should be printed. The user can specify a range of pages to be printed, print quality, number of copies to be printed, and so on.

Note: Print dialog box allows user to select the option only. It does not send the data to printer. To send data to printer use Printer object.

The following are the properties related to Print dialog box.

Property Meaning
Copies Specifies the number of copies to be printed.
FromPage Specifies the value to be displayed in FromPage text box Print dialog box.
ToPage Specifies the value to be displayed in ToPage text box Print dialog box.
Min Specifies the minimum value for page range.
Max Specifies the maximum value for page range.
PrinterDefault Specifies whether the options selected in Print dialog box change the settings of Printer system object.
Table 9.5: Properties of Print dialog box.

Please see on-line documentation for flags that are applicable to Print dialog. The following code allows user to select printing related options and also changes the corresponding settings in Printer system object.

Private Sub CmdPrint_Click()

With CommonDialog1
' enable changes to printer object
.PrinterDefault = True
' you must set Min and Max properties otherwise
' Frompage and ToPage are ignored.
.Min = 1
.Max = 10
.FromPage = 5
.ToPage = 10
' select Pages as the default
.Flags = cdlPDPageNums
.ShowPrinter
' handle printing using Printer Object
End With
End Sub
Listing 9.4: Printing using Print dialog box.

When the above code is run the displayed Print dialog

Help Dialog Box
Unlike other dialog boxes, it doesn’t take any input from user. Instead it runs WINHLP32.EXE program to display help file that is set using HelpFile property.

The following are the properties related to Help dialog box.

Property Meaning
Helpfile Specifies the help file to be used to display help.
Helpkey Specifies the keyword of the topic that is to be displayed.
Helpcommand Specifies the type of online help requested. Please see on-line documentation for valid options.
Table 9.6: Properties related to Help dialog box of Common dialog control


The following listing displays the help file CDPLAYER.HLP that is found in Windows\Help folder.

Private Sub Cmdhelp_Click()
With CommonDialog1
.FileName = "c:\windows\help\cdplayer.hlp"
' display contents of the file initially
.HelpCommand = cdlHelpContents
.ShowHelp
End With
End Sub
Listing 9.5: Code to display help using common dialog control.