I am currently attempting to use the Windows clipboard and its notifications in my application. Specifically, I am attempting to subscribe to the WM_CLIPBOARDUPDATE
window message by using the AddClipboardFormatListener()
function. Previously, I had been using the SetClipboardViewer()
function in order to add my window directly into the clipboard viewer chain. This had worked just fine, and I had received the relevant messages WM_DRAWCLIPBOARD
and WM_DESTROYCLIPBOARD
when expected. However, I would like to avoid continuing to use the clipboard chain because of how volatile it can be.
My understanding was that I would be perfectly able to receive WM_CLIPBOARDUPDATE
after calling AddClipboardFormatListener()
. Is there another step here that I am missing? What do I need to do to make sure that I receive this message properly? As it stands currently, I am not receiving it when performing a copy operation.
Here is an abridged example of what my code looks like:
WNDPROC override:
LRESULT CALLBACK ClipboardService::CallWndProc(int nCode, WPARAM wParam, LPARAM lParam)
{
switch ( pMsg->message )
{
case WM_DRAWCLIPBOARD:
// Handle clipboard available event and forward message
break;
case WM_CLIPBOARDUPDATE:
// This is never triggered
break;
case WM_DESTROYCLIPBOARD:
// Handle clipboard cleared event and forward message
break;
}
return ::CallNextHookEx( g_Hook, nCode, wParam, lParam );
}
Called by Constructor:
HRESULT ClipboardService::SetOrRefreshWindowsHook()
{
HRESULT hr = S_OK;
try
{
if (!m_bHookSet)
{
g_hwndCurrent = ::CreateWindowEx(0, "Message", "ClipboardMessageWindow", 0, 0, 0, 0, 0, HWND_MESSAGE, NULL, NULL, NULL);
m_dwThreadID = ::GetWindowThreadProcessId(g_hwndCurrent, &m_dwProcessID);
_Module.Lock();
SetLastError(0);
g_Hook = ::SetWindowsHookEx(WH_CALLWNDPROC, CallWndProc, 0, m_dwThreadID);
//g_hwndNext = ::SetClipboardViewer(g_hwndCurrent); old way to subscribe
// This is what I expect should subscribe me to WM_CLIPBOARDUPDATE messages
if (!::AddClipboardFormatListener(g_hwndCurrent))
hr_exit(E_UNEXPECTED);
DWORD dwLastError = ::GetLastError();
g_This = this;
m_bHookSet = true;
}
}
catch (...)
{
hr_exit(E_UNEXPECTED);
}
wrapup:
return hr;
}
This is a COM interface that is called by a .NET wrapper, but I don't think that either of those two things are relevant to my problem in this case (figured I would add just in case).
You should not be using SetWindowsHookEx(WH_CALLWNDPROC)
to receive messages to your own window. Use RegisterClass/Ex()
instead to register your own custom window class that has your WndProc
assigned to it, and then CreateWindowEx()
can create an instance of that window class. No hooking needed.
HINSTANCE g_hThisInst = NULL;
HWND g_hwndCurrent = NULL;
//HWND g_hwndNext = NULL;
bool g_AddedListener = false;
BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)
{
g_hThisInst = hinstDLL;
return TRUE;
}
LRESULT CALLBACK ClipboardService::WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg)
{
case WM_CREATE:
//g_hwndNext = ::SetClipboardViewer(hwnd);
g_AddedListener = ::AddClipboardFormatListener(hwnd);
return g_AddedListener ? 0 : -1;
case WM_DESTROY:
/*
ChangeClipboardChain(hwnd, g_hwndNext);
g_hwndNext = NULL;
*/
if (g_AddedListener)
{
RemoveClipboardFormatListener(hwnd);
g_AddedListener = false;
}
return 0;
/*
case WM_CHANGECBCHAIN:
if (g_hwndNext == (HWND)wParam)
g_hwndNext = (HWND)lParam;
else if (g_hwndNext)
SendMessage(g_hwndNext, uMsg, wParam, lParam);
break;
case WM_DRAWCLIPBOARD:
// Handle clipboard available event
if (g_hwndNext)
SendMessage(g_hwndNext, uMsg, wParam, lParam);
break;
*/
case WM_CLIPBOARDUPDATE:
// Handle clipboard updated event
return 0;
case WM_DESTROYCLIPBOARD:
// Handle clipboard cleared event and forward message
break;
}
return ::DefWindowProc(hwnd, uMsg, wParam, lParam);
}
HRESULT ClipboardService::SetOrRefreshWindowsHook()
{
try
{
if (!g_hwndCurrent)
{
WNDCLASS wndClass = {};
wndClass.lpfnWndProc = &ClipboardService::WndProc;
wndClass.hInstance = g_hThisInst;
wndClass.lpszClassName = TEXT("ClipboardMessageWindow");
if (!::RegisterClass(&wndClass))
{
DWORD dwLastError = ::GetLastError();
if (dwLastError != ERROR_CLASS_ALREADY_EXISTS)
return HRESULT_FROM_WIN32(dwLastError);
}
g_hwndCurrent = ::CreateWindowEx(0, wndClass.lpszClassName, "", 0, 0, 0, 0, 0, HWND_MESSAGE, NULL, g_hThisInst, NULL);
if (!g_hwndCurrent)
{
DWORD dwLastError = ::GetLastError();
return HRESULT_FROM_WIN32(dwLastError);
}
g_This = this;
}
}
catch (...)
{
return E_UNEXPECTED;
}
return S_OK;
}