FIX: DelayRenderFileData() Does Not Call OnRenderFileData()

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().

   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);