Drag and Drop in non MFC, c++

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Hello There,
I researched abit about dra and drop and now I have a problem with the message filter of
windows.

basicly I created a MessageProc Callback for handling the droped files as you can see:

C++

bool glob_ret_msgdrop  = false;
bool glob_ret_cpydata = false;
bool glob_ret_49 = false;

LRESULT CALLBACK MsgProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{	
// 	glob_ret_msgdrop = ChangeWindowMessageFilterEx(hwnd, WM_DROPFILES, MSGFLT_ALLOW, nullptr);
// 	glob_ret_cpydata = ChangeWindowMessageFilterEx(hwnd, WM_COPYDATA, MSGFLT_ALLOW, nullptr);
// 	glob_ret_49 = ChangeWindowMessageFilterEx(hwnd, 0x49, MSGFLT_ALLOW, nullptr);

	switch (uMsg)
	{
	case WM_DROPFILES:
		//DDH_main->OnDropFile(uMsg, wParam, lParam);
		MessageBox(NULL, "droped", "none", NULL);
	}
	return DefWindowProc(hwnd, uMsg, wParam, lParam); 
}

but the WM_DROPFILES case never gets called, means the message box never pops up if
a file gets droped into the exe.

So I researched a bit more and noticed that I have to add the filters for win7 and newer versions.

So I do the following in the main(){} function

C++

//loc_hwnd is filled by GetActiveWindow()
		DragAcceptFiles(loc_hwnd, true);		

		//ChangeWindowMessageFilter(WM_DROPFILES, MSGFLT_ADD);
		//ChangeWindowMessageFilter(WM_COPYDATA, MSGFLT_ADD);
		//ChangeWindowMessageFilter(0x0049, MSGFLT_ADD);

		glob_ret_msgdrop = ChangeWindowMessageFilterEx(loc_hwnd, WM_DROPFILES, MSGFLT_ALLOW, nullptr);
		glob_ret_cpydata = ChangeWindowMessageFilterEx(loc_hwnd, WM_COPYDATA, MSGFLT_ALLOW, nullptr);
		glob_ret_49 = ChangeWindowMessageFilterEx(loc_hwnd, 0x49, MSGFLT_ALLOW, nullptr);

the global booleans return all 1, means it should be a success.

But if I drop something onto my exe , nothing happens.
So what did I miss here ?

,greetings Georg

Posted 30-Dec-15 4:53am

GAFO

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Richard MacCutchan · Answer 1 · 2015-12-30T05:51:00

Solution 1

You should study Handling Shell Data Transfer Scenarios (Windows)[^].

Posted 30-Dec-15 5:51am

Richard MacCutchan

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GAFO 30-Dec-15 14:11pm

ok, i will check it out, thank you.
edit: there are many exambles out, but even full solutions dont work anymore, i tried a few http://www.catch22.net/tuts/drop-target
i assume all projects worked once, but not anymore, also tried the ready .exe's just to be sure :/ everywhere i read that windows changed alot for security, thatswhy it became so hard -.-

GAFO · Answer 2 · 2015-12-30T12:02:00

I have a idea which is nearly working:

if I put this into my main function:

C++

DragAcceptFiles(GetActiveWindow(), TRUE);
MSG messages;
MessageBox(NULL, "DragAndDropThread", "", NULL);
while (GetMessage(&messages, NULL, 0, 0))
{
    MessageBox(NULL, "GetMessage", "", NULL);
    /* Translate virtual-key messages into character messages */
    TranslateMessage(&messages);
    /* Send message to WindowProcedure */
    DispatchMessage(&messages);
}

it works buggy, but my main-window gets blocked and only paints black, since
it needs to return something to work in the other threads somehow.

thatswhy I tried the following:

C++

BOOL WINAPI MessageNULLLoopThread(LPVOID lpParameter)
{
	HWND curWindow = (HWND)lpParameter;
	DragAcceptFiles(curWindow, TRUE);

	MSG messages;
	MessageBox(NULL, "DragAndDropThread", "", NULL);
	while (GetMessage(&messages, NULL, 0, 0))
	{
	 	MessageBox(NULL, "GetMessage", "", NULL);
	 	/* Translate virtual-key messages into character messages */
	 	TranslateMessage(&messages);
	 	/* Send message to WindowProcedure */
	 	DispatchMessage(&messages);
	}
	
	return TRUE;
}

And I've put the following into my main function:

C++

CreateThread(0, 0, (LPTHREAD_START_ROUTINE)MessageNULLLoopThread, GetActiveWindow(), 0, 0);

Its not blocking my main window from rendering then, but in that thread
GetActiveWindow() does not work, so i need to pass it down by lParam...

And the GetMessage loop does not work in the new thread, the debug-messagebox
does not get called once inside the loop.

This is getting realy crazy right now -.-

Why does GetActiveWindow() not work in another thread ? Why is the loop not working
if i put it into a thread ?

But most important: how do I fix this ?

Drag and Drop in non MFC, c++

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Drag and Drop in non MFC, c++

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