INFO: Non-Modal Form Support in Visual Basic DLLs

 Last reviewed: August 4, 1997
Article ID: Q171978
The information in this article applies to:
  • Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 5.0

SUMMARY

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

MORE INFORMATION

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. Example: 

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

Keywords          : IAPOLE vb5all VBKBAX VBKBComp kbinfo
Version           : 5.0
Platform          : WINDOWS

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Last reviewed: August 4, 1997
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