BUG: DelayRenderFileData() Does Not Call OnRenderFileData()

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1, 2.2, 4.0, 4.1, 4.2, 5.0, 6.0
  • Microsoft Visual C++ for Windows, 16-bit edition, version 1.52

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. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

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

Additional query words: 0x80040064 [ASCII 150]2147745892

Keywords : kbole kbMFC kbVC kbVC200bug kbVC210bug kbVC220bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug
Version : WINDOWS:1.52; WINNT:2.0,2.1,2.2,4.0,4.1,4.2,5.0,6.0
Platform : WINDOWS winnt
Issue type : kbbug