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Q150034: PRB: LPPICTUREDISP Cannot Be Passed Across Process Boundaries

Article: Q150034
Product(s): Microsoft C Compiler
Version(s): winnt:4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbActiveX kbAutomation kbBitmap kbCOMt kbCtrl kbMFC kbVC400 kbVC500 kbVC600 kbGrpDSMFCA
Last Modified: 30-JUL-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
   - Microsoft OLE Control Developer's Kit (CDK) 
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SYMPTOMS
========

An automation server that implements a Picture object wrapped by the
CPictureHolder class in MFC fails when it attempts to pass a pointer to the
picture object's IPictureDisp implementation across process boundaries.

CAUSE
=====

IPictureDisp gains access to methods of the Picture object that cannot be
marshaled across process boundaries. For example, IPictureDisp supports
DISPID_PICT_RENDER to gain access to the Render method of the Picture object.
The Render method takes a handle to a device context as the first parameter.
Device context handles cannot be marshaled.

Dispatch interfaces can normally be marshalled by using the IDispatch marshaling
code, but the Picture object implements IMarshal specifically to cause its
marshaling to fail.

STATUS
======

This behavior is by design.

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

The ClassWizard in Visual C++ allows you to select a return type of
LPPICTUREDISP for a method. This method might return the IPictureDisp interface
obtained by calling CPictureHolder::GetPictureDispatch. However, if this method
is called by a controller running in another process, the method fails and
returns an error code of E_FAIL.

Because the Picture object causes the marshaling of IPictureDisp to fail,
problems can also occur when trying to obtain an IPictureDisp interface across
thread boundaries in a multiple-thread apartment model object.

REFERENCES
==========

For more information on marshaling, please see "Inside OLE," second edition, by
Kraig Brockschmidt, Chapter 6, "Local/Remote Transparency," published by
Microsoft Press.

Additional query words:

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Keywords          : kbActiveX kbAutomation kbBitmap kbCOMt kbCtrl kbMFC kbVC400 kbVC500 kbVC600 kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:4.0,4.1,4.2,5.0,6.0
Issue type        : kbprb

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