DOCUMENT:Q190076  07-AUG-1998  [vbwin]
TITLE   :HOWTO: Avoid GPF When Using a VB6 DLL with a VB5 UserControl
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:WINDOWS:6.0
OPER/SYS:WINDOWS
KEYWORDS:

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---------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Visual Basic Professional and Enterprise Editions 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
======================================================================
Version           : WINDOWS:6.0
Platform          : WINDOWS
Issue type        : kbhowto

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