Contents
# What is common
dialog control?
# What is an
ActiveX control?
# How to load an
ActiveX control into project?
# How to use Open
and Save As dialog boxes?
# How to use Font
dialog box?
# How to use Color
dialog box?
# How to use Print
dialog box?
# How to display
help file using Help dialog?
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
|
|
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.
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.
Exercises
1.
How do you change the title of Open dialog box?
2.
How do you get the list of
fonts supported by both printer and screen?
3.
What is the significance of Min and Max properties in Font dialog box?
4.
Which property is used to set
the default extension for Save As
dialog?
5.
How do you set red color as the
default color for Color dialog box?
6.
How do you populate Type List box of Open dialog box?
7.
What is the use of PrinterDefault property?
8.
What is the use of setting CdlCFEffects Flag?
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