PRB: Error 371 or 5 Occurs When Using the Show Method

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 5.0

SYMPTOMS

When the MDI child form uses the Show method to open a form, you may receive the following error:

   Run-time Error '371':
   The specified object can't be used as an owner form for Show().

   Run-time Error '5':
   Invalid procedure call or argument.

CAUSE

These errors occur if an MDI child form uses the Show method and specifies that it owns the form to display. An MDI child form cannot own another form.

STATUS

This behavior is by design.

MORE INFORMATION

While you can specify the owner of a form as one of the parameters in the Show method, you cannot designate an MDI Child form as an owner of another form.

Steps to Reproduce Problem

1. Start a new Standard EXE project in Visual Basic. Form1 is created by default.

2. Add a CommandButton to Form1.

3. Add an MDI form and a second form to your project.

4. Set the MDIChild Property of Form1 to True.

   NOTE: To reproduce the error #5, set the MDIChild Property of Form2 to True as well.

5. Copy the following code to the Code window of Form1.

         Option Explicit
   

         Private Sub Command1_Click()
            Form2.Show vbModal, Me
         End Sub
   
   

6. Press the F5 key to run the program. Click the CommandButton and the error occurs.