INFO: Non-Modal Form Support in Visual Basic DLLs

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: