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Overview
The clipboard is used to transfer data between windows or applications. It is used either during Drag/Drop operation or during a Cut/Copy/Paste operation. Whether you are using Drag/Drop or Cut/Copy/Paste, the code used to place data on the clipboard is very similar. This article will show you the basics for accessing the clipboard.
Placing Data on the Clipboard
Writing to the Clipboard is straightforward. By following a few simple steps you can place nearly any supported clipboard format onto the clipboard.
- Create a new COleDataSource.
- Create a new CSharedFile (see initialization in example below).
- Write info to the CSharedFile instance.
- Detach the memory associated with the CSharedFile.
- Pass the detached memory and format info to CacheGlobalData().
- Place the data on the clipboard using SetClipboard().
Example 1 – Source for Writing to Clipboard
void CClipExamView::OnEditCopy()
{
COleDataSource* pSource = new COleDataSource();
CSharedFile sf(GMEM_MOVEABLE|GMEM_DDESHARE|GMEM_ZEROINIT);
CString text = _T(“Testing 1… 2… 3…”);
sf.Write(text, text.GetLength()); // You can write to the clipboard as you would to any CFile
HGLOBAL hMem = sf.Detach();
if (!hMem) return;
pSource-CacheGlobalData(CF_TEXT, hMem);
pSource-SetClipboard();
}
Serializing to the Clipboard
Often it is useful to be able to serialize your data to the clipboard so that you can create a custom clipboard for your application. This can be done by registering a custom clipboard format and serializing to a CSharedFile. The following source illustrates how to serialize a CObject to the clipboard.
Example 2 – Serializing to the Clipboard
void SerializeToClipboard(CObject* obj, CString formatname )
{
COleDataSource* pSource = new COleDataSource();
CSharedFile sf(GMEM_MOVEABLE|GMEM_DDESHARE|GMEM_ZEROINIT);
UINT format = RegisterClipboardFormat(formatname);
CArchive ar(&sf, CArchive::store);obj-Serialize(ar);
ar.Close();HGLOBAL hMem = sf.Detach();
if (!hMem) return;
pSource-CacheGlobalData(format, hMem);
pSource-SetClipboard();
}
Reading Data from the Clipboard
Reading data from the clipboard is nearly the inverse of placing data on the clipboard.
- Create a COleDataObject instance.
- Check to see if the format you want is available.
- Place the data associated with the clipboard into a CMemFile.
- Read the data out of the CMemFile.
- Release the global memory.
Example 3 – Reading Data from the Clipboard
void CClipExamView::OnEditPaste()
{
COleDataObject obj;
if (obj.AttachClipboard()) {
if (obj.IsDataAvailable(CF_TEXT)) {
HGLOBAL hmem = obj.GetGlobalData(CF_TEXT);
CMemFile sf((BYTE*) ::GlobalLock(hmem), ::GlobalSize(hmem));
CString buffer;
LPSTR str = buffer.GetBufferSetLength(::GlobalSize(hmem));
sf.Read(str, ::GlobalSize(hmem));
::GlobalUnlock(hmem);
// Do something with the data in ‘buffer’
TRACE(“Paste received = ‘%s’rn”, buffer);
}
}
}
Serializing from the Clipboard
Serializing from the Clipboard is only a slight modification of the previous example.
Example 4 – Reading Serialized Data from the Clipboard
void SerializeFromClipboard(COleDataObject* obj, CObject* cobj, CString formatname)
{
UINT format = RegisterClipboardFormat(formatname);if (obj-IsDataAvailable(format)) {
HGLOBAL hmem = obj-GetGlobalData(format);
CMemFile sf((BYTE*) ::GlobalLock(hmem), ::GlobalSize(hmem));
CArchive ar(file, CArchive::load);
cobj-Serialize(ar);
ar.Close();
::GlobalUnlock(hmem);
}
}
Drag/Drop Support
All of the examples thus far are placing the data on the clipboard as if a copy operation had been invoked. Enabling Drag/Drop is a simple change to the above code.
Sourcing a Drag/Drop
The code for the origination of a drag/drop is identical to examples for placing data on the clipboard, with one little modification. Rather than executing the SetClipboard() command, you should execute the DoDragDrop() command.
Example 5 – Sourcing a Drag/Drop
// Initiate the Drag/Drop
void CClipExamView::OnLButtonDown(UINT nFlags, CPoint point)
{
COleDataSource* pSource = new COleDataSource();
CSharedFile sf(GMEM_MOVEABLE|GMEM_DDESHARE|GMEM_ZEROINIT);
CString text = _T(“Testing 1… 2… 3…”);sf.Write(text, text.GetLength()); // You can write to the clipboard as you would to any CFile
HGLOBAL hMem = sf.Detach();
if (!hMem) return;
pSource-CacheGlobalData(CF_TEXT, hMem);
pSource-DoDragDrop();
}
Accepting a Drag/Drop
Example 5 – Accepting a Drag/Drop
// OnDragOver – Called when mouse moves over window during a Drag/Drop
DROPEFFECT CClipExamView::OnDragOver(COleDataObject* pDataObject, DWORD dwKeyState, CPoint point)
{
if (pDataObject-IsDataAvailable(CF_TEXT)) {
return DROPEFFECT_COPY;
}
return DROPEFFECT_NONE;
}
// OnDrop – Called when drop occurs
BOOL CClipExamView::OnDrop(COleDataObject* pDataObject, DROPEFFECT dropEffect, CPoint point)
{
if (pDataObject-IsDataAvailable(CF_TEXT)) {
HGLOBAL hmem = pDataObject-GetGlobalData(CF_TEXT);
CMemFile sf((BYTE*) ::GlobalLock(hmem), ::GlobalSize(hmem));
CString buffer;
LPSTR str = buffer.GetBufferSetLength(::GlobalSize(hmem));
sf.Read(str, ::GlobalSize(hmem));
::GlobalUnlock(hmem);
// Do something with the data in ‘buffer’ Housekeeping Issues
TRACE(“OnDrop received = ‘%s’rn”, buffer);
return TRUE;
}
return FALSE;
}
A few additional housekeeping things must be done make drag/drop work correctly.
- Make sure that your applications InitInstance() member function calls the AfxOleInit() function.
- The view must be registered as a drag/drop target. If you don’t do this you won’t be able to accept a drag/drop. See Example 6.
- Several includes must be added to stdafx.h to insure that your code will compile. See Example 7.
Example 6 – Initializing View as Drop Target Example 7 – Include to Add to stdafx.h
// Enable view as a drop target. Assumes COleDropTarget m_DropTarget is defined in view object.
void CClipExamView::OnInitialUpdate()
{
CView::OnInitialUpdate();
m_DropTarget.Register(this);
}
#include <afxole.h> // MFC OLE classes
#include <afxodlgs.h> // MFC OLE dialog classes
#include <afxdisp.h > // MFC OLE automation classes
#include <afxpriv.h>
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