FIX: Creating More Than Two MDI Children Throws WFCException

• Microsoft Visual J++, version 6.0

SYMPTOMS

When creating more than two Multiple Document Interface (MDI) child windows in the constructor of the parent window, a WFCException is thrown with a message that an error has occurred creating a window handle.

CAUSE

This problem is related to the time at which the Win32 window handles are created, which may not be the same time the child window objects are created in Java code.

RESOLUTION

To work around this problem, limit the number of child windows created in the constructor of the parent to two, and/or create child windows after the parent has been constructed. A third option is to use Control.invokeAsync() as illustrated in the commented code in the sample below.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

This bug was corrected in Visual Studio 6.0 Service Pack 3. For more information about Visual Studio service packs, please see the following articles in the Microsoft Knowledge Base:

Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

Q194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

MORE INFORMATION

In WFC, handle creation for children of an MDI parent is deferred until the parent Form is made visible.

Steps to Reproduce Behavior

import com.ms.wfc.app.*;
import com.ms.wfc.core.*;
import com.ms.wfc.ui.*;

public class Form1 extends Form
{
  public Form1()
  {
    initForm();		
    createKids();
  }
  
  protected void onCreateHandle(Event e)
  {
    super.onCreateHandle(e);
    //uncomment the following line for workaround
    //invokeAsync(new MethodInvoker(createKids));
  }
  
  public void createKids()
  {
    for (int i = 0; i < 3; i++)
    {
      Form f = new Form();
      f.setMDIParent(this);
      f.show();
    }
  }

  public void dispose()
  {
    super.dispose();
    components.dispose();
  }

  /**
   * NOTE: The following code is required by the Visual J++ form
   * designer. It can be modified using the form editor. Do not
   * modify it using the code editor.
   */ 
  Container components = new Container();

  private void initForm()
  {
    this.setText("Form1");
    this.setAutoScaleBaseSize(new Point(5, 13));
    this.setClientSize(new Point(292, 273));
    this.setIsMDIContainer(true);
  }

  public static void main(String args[])
  {
    Application.run(new Form1());
  }
} 

REFERENCES

For the latest Knowledge Base articles and other support information on Visual J++ and the SDK for Java, please see the following pages on the Microsoft Technical Support site:

http://support.microsoft.com/support/visualj/

http://support.microsoft.com/support/java/

Additional query words:

Keywords          : kbservicepack kbCtrlCreate kbSDKJava kbVJ600bug kbWFC kbGrpJava kbVS600sp2 kbVS600SP1 kbVS600sp3fix 
Version           : WINDOWS:6.0
Platform          : WINDOWS 
Issue type        : kbbug 

Last Reviewed: July 13, 1999