BUG: An MDI child form may not maximize if the child form contains an ActiveX control in Visual Studio .NET 2003

• The MDI child form may not maximize.
• You cannot change focus to another inactive MDI child form if you click the client area of the inactive MDI child form.

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• You work with Microsoft Windows forms in MDI mode in Visual Studio .NET 2003.
• You use an ActiveX control in an MDI child form.

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Method 1

• To maximize a child form, change the code in step 14 of the "More Information" section to the following:

  Dim frm As Form2
  frm = New Form2
  frm.MdiParent = Me
  frm.WindowState = FormWindowState.Maximized
  frm.Show()

  Note The MdiParent property is used to specify that the Form2 form is a child form.
• To obtain the focus of an inactive child form by clicking the client area of the child form, add code to the child form:
  1. In Solution Explorer, right-click the Form2.vb file, and then click View Code.
  2. Locate the following code in the Form2 class:

     Public Class Form2
         Inherits System.Windows.Forms.Form

  3. Add the following code after the code that you located in step 2:

     Private Const WM_MOUSEACTIVATE As Integer = &H21
     
         Protected Overrides Sub WndProc(ByRef m As Message)
             If m.Msg = WM_MOUSEACTIVATE Then
                 Me.Focus()
             End If
             MyBase.WndProc(m)
     End Sub

     The WM_MOUSEACTIVATE message is sent when the pointer is in an inactive window and the user clicks a mouse button. The WndProc method activates the current MDI child form if the WndProc method receives the WM_MOUSEACTIVATE message.

Method 2

1. In Solution Explorer, right-click the Form2.vb file, and then click View Code.
2. Locate the following code in the Form2 class:

   Public Class Form2
       Inherits System.Windows.Forms.Form

3. Add the following code after the code that you located in step 2:

   Public Sub New(ByVal mdiParent As Form, ByVal initialState As FormWindowState)
           MyBase.New()
   
           Me.MdiParent = mdiParent
           Me.WindowState = initialState
   
           InitializeComponent()
   
   End Sub

   The constructor initializes the MdiParent property of the child form to specify the parent form. The constructor also initializes the WindowState property of the child form before the constructor calls the InitializeComponent method.
4. Change the code in step 14 of the "More Information" section to the following:

   Dim frm As Form2
   frm = New Form2(Me, FormWindowState.Maximized)
   frm.Show()

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Steps to reproduce the behavior

1. Start Visual Studio .NET 2003.
2. On the File menu, point to New, and then click Project. The New Project dialog box appears.
3. Under Project Types, click Visual Basic Projects, and then click Windows Application under Templates.
4. In the Name box, type MyMDIProject, and then click OK. By default, a form that is named Form1 is created.
5. On the Project menu, click Add Windows Form, and then click Open. By default, a form that is named Form2 is created.
6. On the View menu, click Toolbox.
7. Right-click the toolbox, and then click Add/Remove Items. The Customize Toolbox dialog box appears.
8. In the Customize Toolbox dialog box, click the COM Components tab.
9. On the COM Components tab, double-click Microsoft Date and Time Picker Control 6.0 (SP6), and then click OK. The Microsoft Date and Time Picker Control 6.0 (SP6) appears under My User Controls in the toolbox.
10. Double-click Microsoft Date and Time Picker Control 6.0 (SP6) to add the Microsoft Date and Time Picker Control 6.0 (SP6) control to the Form2.
11. In the Properties dialog box of the Form1, set the IsMdiContainer property to true.
12. Add a MainMenu control to the Form1.
13. Click MainMenu control and set the Text property of MenuItem1 to New.
14. On the Form1 form, double-click New, and then add the following code to the MenuItem1_Click event handler in the Form1 form:

    Dim frm As Form2
    frm = New Form2
    frm.WindowState = FormWindowState.Maximized
    frm.MdiParent = Me
    frm.Show()

15. On the File menu, click Save All to save all the files.
16. On the Build menu, click Build Solution.
17. On the Debug menu, click Start.
18. Click New on the menu bar of the Form1. A Form2 child window appears.
    
    The Form2 window is not maximized. However, you can maximize it manually. If you have multiple MDI child forms, you cannot change focus to another child form by clicking the client area of the child form. However, you can change the focus if you click the title bar of the inactive child form.

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