* VB-CODE (1)
Tip 79: Closing All MDI Child Windows at One Time
May 8, 1995
This article explains how you can simultaneously close all child
windows of a running Visual Basic® application.
Using the Count Property of MDI Forms
The multiple document interface (MDI) feature of Visual Basic® allows
you to create applications that have multiple forms within a single
parent form. This allows you to use the multitasking functions of the
Windows® operating system in your programs.
The Windows Notepad is an example of an MDI application. You can open
several text files at one time and move between each document with a
click of the mouse.
When you create a child form while your program is executing, you must
also remember to close all the open child windows before your
application terminates. Otherwise, you could cause some unforeseen
problems with other applications.
The count property of a control, such as a form, can be used to
determine how many members of that particular collection exist. In
this case, the collection refers to the child forms of the parent
form. We can, therefore, determine how many child forms exist in our
application program by executing a statement such as:
X = Forms.Count
After this statement executes, the variable X will contain the number
of child forms that we have created. It is important to decrement this
value by one because the count starts with the value of one, not zero.
Once we know how many child forms we have created within our
application program, we can use the TypeOf statement in a loop to
close each child form that exists. The TypeOf statement is used to
determine the type of object you are dealing with. In this case, we
want to find out if the object is a form (Form1, the name of the
The final step to removing the child forms from the parent form is to
use the Unload statement. Therefore, to remove all child forms from
our program while it is running, we simply check each object in the
form, making sure that it is indeed a child form of the MDI form, and
execute an Unload statement to close the form.
The following program shows how to close all child forms at one time.
Run the program by pressing the F5 function key. The MDIForm1 form is
displayed. Double-click the client area of MDIForm1 to create a child
form (Form1). Do this until you have several child forms visible on
the screen. Click the "Close Children" menu option to close all child
1. Create a new project in Visual Basic. Form1 is created by default.
Set the MDIChild property to True.
2. From Visual Basic's Insert menu, click "MDI Form" to create a
Multiple Document Interface form. MDIForm1 is created by default.
3. Add the following code to the DblClick event for MDIForm1:
Private Sub MDIForm_DblClick()
Dim X As New Form1
4. From Visual Basic's Tools menu, click Menu Editor. Set the Caption
field to "&Close Children" and the Name field to "mnuClose".
5. Add the following code to the mnuClose_Click event:
Private Sub mnuClose_Click()
Dim X As Integer
For X = (Forms.Count - 1) To 0 Step -1
If TypeOf Forms(X) Is Form1 Then
6. From Visual Basic's Tools menu, select Project Options. Set the
StartUp Form to MDIForm1.
"Opening and Closing MDI Windows." (Product Documentation, SDKs, The
Windows Interface GuidelinesA Guide for Designing Software)