Traditionally, developers have used the WM_DROPFILES message to handle
files dropped from the File Manager or Windows Explorer. This message is
sent when the user drops a file on the window of an application that has
registered itself as a recipient of dropped files.
OLE drag and drop supports this same functionality. Both techniques involve
passing a global HDROP (drop structure handle) from the source to the
target. WM_DROPFILES passes this handle in the WPARAM value. OLE drag and
drop passes the HDROP with the data object.
This article demonstrates how to get the dropped file names using OLE drag
and drop. The information in this article supplements the following
Microsoft Knowledge Base article:
135299 (http://support.microsoft.com/kb/135299/) How to add OLE drag-and-drop functionality to a pre-existing MFC application
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To retrieve the dropped file names from a drop source, modify the sample
code included with Microsoft Knowledge Base article 135299 as follows.
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Sample code
// OnDrop is called by OLE DLLs when an item is dropped in a window
// that is registered with the OLE DLLs.
//
BOOL COleEditDropTarget::OnDrop(CWnd* pWnd, COleDataObject* pDataObject,
DROPEFFECT dropEffect, CPoint point )
{
HGLOBAL hGlobal;
LPCSTR pData;
FORMATETC fmtetc =
{ CF_HDROP, NULL, DVASPECT_CONTENT, -1, TYMED_HGLOBAL };
STGMEDIUM stgmed;
TCHAR szFileName[_MAX_PATH + 1];
if(pDataObject->GetData(CF_HDROP, &stgmed, &fmtetc))
{
HDROP hdrop = (HDROP)GlobalLock(stgmed.hGlobal);
if (NULL != hdrop)
{
UINT nFiles = DragQueryFile(hdrop, (UINT)-1, NULL, 0);
for(UINT nNames = 0; nNames < nFiles; nNames++)
{
ZeroMemory(szFileName, _MAX_PATH + 1);
DragQueryFile
(hdrop, nNames, (LPTSTR)szFileName, _MAX_PATH + 1);
// Do something with szFileName.
}
GlobalUnlock(hdrop);
}
ReleaseStgMedium(&stgmed);
return TRUE;
} else {
// Get text data from ColeDataObject.
hGlobal=pDataObject->GetGlobalData(CF_TEXT);
// Get a pointer to data.
pData=(LPCSTR)GlobalLock(hGlobal);
ASSERT(pData!=NULL);
// Set text in the dropped window.
((CEdit*)pWnd)->SetWindowText(pData);
// Unlock memory.
GlobalUnlock(hGlobal);
return TRUE;
}
}
(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by
Robert Duke, Microsoft Corporation.
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