Q190076: HOWTO: Avoid GPF When Using a VB6 DLL with a VB5 UserControl

Article: Q190076
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:6.0
Operating System(s): 
Keyword(s): kbGrpDSVB
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Professional Edition for Windows, version 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 
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SUMMARY
=======

When a PropertyBag interface is passed out of a Visual Basic 5.0 UserControl
into a Visual Basic 6.0 DLL, and the Visual Basic 6.0 server uses the Contents
property of the PropertyBag interface, the server produces the following error:

  Compile error: Function of interface marked as restricted, or the function
  uses as Automation type not supported in Visual Basic.

MORE INFORMATION
================

A PropertyBag object is passed into an object through the ReadProperties and
WriteProperties events in order to save and restore the state of the object. The
problem described in this article occurs when a Visual Basic 5.0 PropertyBag
interface is passed into a Visual Basic 6.0 server, which then attempts to
de-reference a non-existent VTable entry for the Contents property.

This occurs because the Contents property of the PropertyBag interface in version
6.0 did not exist in version 5.0.

To avoid binary incompatibility when inter-mixing Visual Basic 5.0 and Visual
Basic 6.0 components, use the PropertyBag_VB5 interface in Visual Basic 6.0
projects and do not use the Contents property.

Steps to Reproduce Behavior
---------------------------

1. Create a new Visual Basic 6.0 ActiveX DLL project. A project named Project1
  and a class module named Class1 are created by default. From the Properties
  Page, change the project Name property to PropHandler2.

2. From the Class1(Code) window, enter the following code:

        Public Sub Test(obj As PropertyBag)
           Dim vnt As Variant
           vnt = obj.Contents
           obj.Contents = vnt
        End Sub

3. From the File menu, choose Make PropHandler2.dll to build PropHandler2.dll.
  In the Make Project dialog, make a note of the DLL file name and directory
  where the DLL is saved, then choose OK.

4. Create a new Visual Basic 5.0 ActiveX Control project. UserControl1 is
  created by default.

5. The reference to the DLL built in step 3 now needs to be added to the ActiveX
  Control project. From the Project menu, choose References, and then add the
  reference to PropHandler2.dll. To do this, scroll down the list of available
  references to find PropHandler2 and check its checkbox. Then choose OK.

  NOTE: If PropHandler2 is not found, click on Browse and go to the directory in
  which PropHandler2.dll was built. Enter PropHandler2.dll as the File name,
  then choose Open.

6. From the UserControl1(Code) window, enter the following code:

        Private Sub UserControl_WriteProperties(PropBag As PropertyBag)
           Dim obj As New Class1
           obj.Test PropBag
        End Sub

7. Close the control's design window. To do this, from the Project window,
  double-click UserControl1 to bring its designer to the front, then press
  CTRL+F4 to close the window. Closing the designer's window puts the
  UserControl1 control in run mode. As soon as the control is in run mode, its
  icon (the default toolbox icon for a user control) is enabled in the Toolbox.

8. From the File menu, choose Add Project. Add a new Standard EXE project named
  Project2. Form1 is created by default.

9. From the Toolbox, place the UserControl on Form1.

10. From the File menu, choose Save Project2. At the Save File As dialog, choose
  Save. Note that the above compile error will be received.

Additional query words: kbDSupport kbCtrl kbVBp kbVBp600 kbdss kbVBp500

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Keywords          : kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVBA600 kbVB600
Version           : WINDOWS:6.0
Issue type        : kbhowto

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