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Q185675: FIX: DelayRenderFileData() Does Not Call OnRenderFileData()

Article: Q185675
Product(s): Microsoft C Compiler
Version(s): 1.52,2.0,2.1,2.2,4.0,4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbole kbActiveX kbMFC kbVC200bug kbVC210bug kbVC220bug kbVC400bug kbVC410bug kbVC420bug
Last Modified: 11-FEB-2002

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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 2.0, 2.1, 2.2, 4.0, 4.1 
   - Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
   - Microsoft Visual C++ for Windows, 16-bit edition, version 1.52 
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SYMPTOMS
========

In OLE drag-and-drop, when using COleDataSource::DelayRenderFileData() with the
default second parameter of NULL, COleDataSource::OnRenderFileData() may not be
called to request the actual data.

CAUSE
=====

When you call COleDataSource::DelayRenderFileData() with a clipboard format such
as CF_TEXT (or any other clipboard format) and the second parameter FORMATETC is
not specified (defaulting to NULL), _AfxFillFormatEtc() gets called. This
function creates a FORMATETC structure and populates it with default values--it
fills the "tymed" member of the FORMATETC structure with -1. Because the "tymed"
member is a DWORD, the value is effectively 0xffffffff, and therefore all TYMED
enumerations are supported.

However, COleDataSource::OnRenderFileData() or your override for this function,
is called only if the user of this data requests the data with a TYMED value of
TYMED_ISTREAM or TYMED_HGLOBAL.

Because DelayRenderFileData() specified that all the TYMED enumerations are
acceptable, a client may in fact ask for data with a TYMED value other than
TYMED_ISTREAM or TYMED_HGLOBAL. This results in an HRESULT of DATA_E_FORMATETC
being returned from IDataObject::GetData().

RESOLUTION
==========

The workaround is to call COleDataSource::DelayRenderFileData() with the second
parameter explicitly specified. For example:

     FORMATETC fmt = {CF_TEXT, NULL, DVASPECT_CONTENT, -1,
        TYMED_ISTREAM|TYMED_HGLOBAL};

     // Class derived from ColeDataSource.
     COleMyDataSource *pDataSrc;
     pDataSrc = new COleMyDataSource();
     pDataSrc->DelayRenderFileData(CF_TEXT, &fmt);

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

This problem was corrected in Microsoft Visual C++ .NET.

(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Jaganathan
Thangavelu, Microsoft Corporation

Additional query words: 0x80040064 [ASCII 150]2147745892

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Keywords          : kbole kbActiveX kbMFC kbVC200bug kbVC210bug kbVC220bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug kbGrpDSMFCATL kbNoUpdate 
Technology        : kbAudDeveloper kbMFC
Version           : :1.52,2.0,2.1,2.2,4.0,4.1,4.2,5.0,6.0
Issue type        : kbbug
Solution Type     : kbfix

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