ActiveX Control Fails in Visual Basic but Works Fine in MFC

• Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 4.2
• Microsoft Visual C++, 32-bit Edition, versions 4.0, 4.1, 4.2
• Microsoft Visual Basic Standard Edition for Windows, version 4.0

SUMMARY

This article documents known problems that can cause an ActiveX control to fail to work in Visual Basic for Windows while still allowing the control to work successfully in an MFC control container.

MORE INFORMATION

Occasionally an ActiveX control works successfully in an MFC control container but fails when used in Visual Basic. The failure in Visual Basic is usually caused by a problem with the control. The following are known problems that can cause this type of behavior.

• The control has been created with the simple frame option specified in ControlWizard but there is no call to the COleControl::EnableSimpleFrame method.
  
  By default, if the simple frame option is specified, ControlWizard adds a call to EnableSimpleFrame to the COleControl-derived class's constructor. ControlWizard also adds the OLEMISC_SIMPLEFRAME MiscStatus bit to the status bits for the control. If the call to EnableSimpleFrame is removed but the OLEMISC_SIMPLEFRAME MiscStatus bit is still specified, Visual Basic crashes with an Access Violation when the control is added to a form.
  
  If the OLEMISC_SIMPLEFRAME MiscStatus bit is turned on for a control, the COleControl::EnableSimpleFrame method must be called.



• The control has been given a property that is declared as type BSTR in the control's .odl file, but which is really of some other type, such as long, short, or double. Typically this kind of type mismatch happens when the .odl file for the control has been manually edited rather than letting ClassWizard handle the adding and removing of properties.
  
  In order for the problem to occur, the property must have been added via ClassWizard as a non-BSTR type and have been implemented as a member variable, not as Get/Set methods. If the control's .odl file is manually edited and the type of the property is then changed to BSTR but the corresponding control member variable type and dispatch map entry are not changed to reflect the new type, Visual Basic can crash with an Access Violation when the control is added to a form.



• A control implements a property, event, or method that has the same name as one of Visual Basic's extended properties, events, or methods.
  
  For example, if the control implements properties named DragIcon or DragMode, the problem might occur.
  
  To avoid the problem, rename the conflicting property, event, or method.

Additional query words: VB OCX

Keywords          : kbole kbMFC kbVC kbVC400 kbVC410 kbVC420 
Version           : Windows NT:4.0,4.1,4.2
Platform          : winnt 
Issue type        : kbinfo 

Last Reviewed: July 29, 1999