BUG: Hidden MDIChild Form Can Still Be Active Form

• Standard, Professional, and Enterprise Editions of Microsoft Visual Basic, 32-bit only, for Windows, version 4.0

SYMPTOMS

Under certain circumstances, an MDIChild form can be hidden but still be the active form. This occurs when an MDIChild form is shown before hiding the active MDIChild form. The latter MDIChild form stays active although it is invisible. Clicking in an area of the invisible form does not activate a visible form behind it because the input is sent to the invisible form.

STATUS

Microsoft has confirmed this to be an issue in the Microsoft products listed at the beginning of this article. Microsoft is researching this issue and will post new information here in the Microsoft Knowledge Base as it becomes available.

WORKAROUND

If you are going to hide an MDIChild form and then show another form, it is important to hide the existing form first, and then show the new MDIChild form.

For example, instead of the code:

   Form3.Show

   Me.Hide

   Me.Hide

   Form3.Show

MORE INFORMATION

Steps to Reproduce Problem

1. Start a new project in Visual Basic. Form1 is created by default. Select the Insert/Form menu option twice and insert an MDI parent form by selecting Insert/MDI Form.

2. Change the MDIChild property of all three regular forms to True. Place a Command button on Form1 and Form2. In the Click event of the Command button on Form1, place the following code:

      Private Sub Command1_Click()
   
         Form2.Show
   
      End Sub
   
   

3. In the Click event of the Command button on Form2, place the following code:

      Private Sub Command1_Click()
   
        Form3.Show
   
        Me.Hide
   
      End Sub
   
   

4. Run the project by pressing the F5 key. Click on the Command button of Form1 to show Form2. Move Form2 so it only partially covers Form1. For example, have it cover the lower right hand corner of Form1. Click on the Command button on Form2 to show Form3 and hide Form2. Click on the lower right hand corner of Form1. Form1 is not activated.

   Private Sub Command1_Click()

      Me.Hide

   Form3.Show

   End Sub