Microsoft KB Archive/171978

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INFO: Non-Modal Form Support in Visual Basic DLLs

Article ID: 171978

Article Last Modified on 1/9/2003


  • Microsoft Visual Basic 5.0 Professional Edition
  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition

This article was previously published under Q171978


Visual Basic 4.0 ActiveX DLLs (in-process ActiveX Servers) could display forms modally only. Visual Basic versions 5.0 and later allow you to display forms modally or in modeless form. When designing a ActiveX DLL, you have to take into consideration whether the client application supports displaying modeless forms.


Modeless forms displayed by in-process components cannot function correctly unless they can communicate with the client's message loop. Therefore, in- process components created with Visual Basic can display modeless forms only in client processes that support such communication.

The following applications support the display of modeless forms by in- process components:

  • Applications created with Visual Basic 5.0 or later.
  • Microsoft Office 97 or later.
  • Applications that have the Visual Basic Technology logo.(Those that license Visual Basic for Applications version 5.0 or later.)

Applications that do not support the display of modeless forms by in- process components include:

  • Applications created with earlier versions of Visual Basic.
  • Earlier versions of Microsoft Office.
  • Version 3.0 of Microsoft Internet Explorer.

To allow in-process components to detect at run time whether a client application supports the display of modeless forms, Visual Basic provides the Boolean NonModalAllowed property of the App object.

An in-process component should test this property before showing a modeless form. If the value is True, the form can be shown vbModeless. If the value is False, showing a modeless form will cause run-time error 369. The component should degrade gracefully by showing the form vbModal instead.

For example:

   If App.NonModalAllowed Then
      Form1.Show vbModeless
      Form1.Show vbModal

Additional query words: kbVBp500 kbVBp600 kbVBp kbdsd kbDSupport kbNoKeyWord

Keywords: kbinfo KB171978