Send HDROP data with WM_DROPFILES message.

[Joseph Scandura]

We assume MS SoundRecorder is running and the file
c:\temp\test.wav exists.

We're trying to send a WM_DROPFILES message to MS
SoundRecorder.
We don't know exactly the format of the structure to send
as an HDROP parameter to the SendMessage (hWndSoundRec,
WM_DROPFILES, (WPARAM) &oMedium, 0L) function.

The message is actually recieved by the Sound Recorder.
However it pops up a message saying:
"File cannot be opened" with random characters (indicating
reading from a non-allocated, or corrupted memory
location) at the end.

We're using the structures STGMEDIUM and DROPFILES as
below.

What are we missing?


int main(int argc, char* argv[])
{
HWND hWndSoundRec = FindWindow ("SoundRec", NULL);

if (hWndSoundRec)
{
HGLOBAL hGlobal = GlobalAlloc (GMEM_FIXED,
sizeof ("k:\\temp\\test.wav") + 2);
char *strFile = (char*) GlobalLock
(hGlobal);
strcpy (strFile, "c:\\temp\\test.wav");
strFile [strlen ("c:\\temp\\test.wav") +
1] = NULL;

POINT point;
point.x = 100;
point.y = 100;

DROPFILES oDropFiles;
oDropFiles.pFiles = (long) &strFile;
oDropFiles.fNC = FALSE;
oDropFiles.fWide = FALSE;
oDropFiles.pt = point;


STGMEDIUM oMedium;
oMedium.tymed = 1;
oMedium.hGlobal = &oDropFiles;

//Send Message with a file reference.
BOOL bSent = SendMessage (hWndSoundRec,
WM_DROPFILES, (WPARAM) &oMedium, 0L);

BOOL bRet = GlobalUnlock (hGlobal);
GlobalFree (hGlobal);
}
return 0;
}

[Henk Devos]

wParam should be a HGLOBAL not a STGMEDIUM.
i.e. use the hGlobal you have as the wParam.

Henk Devos
http://www.whirlingdervishes.com

Post by Joseph Scandura
We assume MS SoundRecorder is running and the file
c:\temp\test.wav exists.
We're trying to send a WM_DROPFILES message to MS
SoundRecorder.
We don't know exactly the format of the structure to send
as an HDROP parameter to the SendMessage (hWndSoundRec,
WM_DROPFILES, (WPARAM) &oMedium, 0L) function.
The message is actually recieved by the Sound Recorder.
"File cannot be opened" with random characters (indicating
reading from a non-allocated, or corrupted memory
location) at the end.
We're using the structures STGMEDIUM and DROPFILES as
below.
What are we missing?
int main(int argc, char* argv[])
{
HWND hWndSoundRec = FindWindow ("SoundRec", NULL);
if (hWndSoundRec)
{
HGLOBAL hGlobal = GlobalAlloc (GMEM_FIXED,
sizeof ("k:\\temp\\test.wav") + 2);
char *strFile = (char*) GlobalLock
(hGlobal);
strcpy (strFile, "c:\\temp\\test.wav");
strFile [strlen ("c:\\temp\\test.wav") +
1] = NULL;
POINT point;
point.x = 100;
point.y = 100;
DROPFILES oDropFiles;
oDropFiles.pFiles = (long) &strFile;
oDropFiles.fNC = FALSE;
oDropFiles.fWide = FALSE;
oDropFiles.pt = point;
STGMEDIUM oMedium;
oMedium.tymed = 1;
oMedium.hGlobal = &oDropFiles;
file://Send Message with a file reference.
BOOL bSent = SendMessage (hWndSoundRec,
WM_DROPFILES, (WPARAM) &oMedium, 0L);
BOOL bRet = GlobalUnlock (hGlobal);
GlobalFree (hGlobal);
}
return 0;
}

[Jim Barry]

Post by Joseph Scandura
We're trying to send a WM_DROPFILES message to MS
SoundRecorder.
We don't know exactly the format of the structure to send
as an HDROP parameter to the SendMessage (hWndSoundRec,
WM_DROPFILES, (WPARAM) &oMedium, 0L) function.
The message is actually recieved by the Sound Recorder.
"File cannot be opened" with random characters (indicating
reading from a non-allocated, or corrupted memory
location) at the end.

As Henk correctly points out, the WPARAM should be an HGLOBAL containing the DROPFILES structure. Try the following code snippet. It seems to be important to use PostMessage rather than SendMessage, I'm not too sure why that is.

int main(int argc, char* argv[])
{
if (HWND hwnd = FindWindow ("SoundRec", 0))
{
char filename[] = "c:\\temp\\test.wav";
if (HGLOBAL hGlobal =
GlobalAlloc(GHND, sizeof(DROPFILES) + strlen(filename) + 2))
{
DROPFILES * df = static_cast<DROPFILES *>(GlobalLock(hGlobal));
df->pFiles = sizeof(DROPFILES);
strcpy(reinterpret_cast<char *>(df + 1), filename);
GlobalUnlock(hGlobal);
if (!PostMessage(hwnd, WM_DROPFILES, (WPARAM)hGlobal, 0))
GlobalFree(hGlobal);
}
}
return 0;
}

[ilm]

Post by Joseph Scandura
int main(int argc, char* argv[])
{
if (HWND hwnd = FindWindow ("SoundRec", 0))
{
char filename[] = "c:\\temp\\test.wav";
if (HGLOBAL hGlobal =
GlobalAlloc(GHND, sizeof(DROPFILES) + strlen(filename) + 2))
{
DROPFILES * df = static_cast<DROPFILES *>(GlobalLock(hGlobal));
df->pFiles = sizeof(DROPFILES);
strcpy(reinterpret_cast<char *>(df + 1), filename);
GlobalUnlock(hGlobal);
if (!PostMessage(hwnd, WM_DROPFILES, (WPARAM)hGlobal, 0))
GlobalFree(hGlobal);
}
}
return 0;
}

Hey, that's extremely interesting. I suppose a similar technique could
be used to "relay" any WM_DROPFILES message my window receives to a
window in another process? Any idea how that would look like?

Simon

[Jim Barry]

Post by ilm
Hey, that's extremely interesting. I suppose a similar technique could
be used to "relay" any WM_DROPFILES message my window receives to a
window in another process? Any idea how that would look like?

How do you mean, other than making sure that DefWindowProc does not get a chance to free the HGLOBAL before it reaches the target?

[ilm]

Post by Jim Barry

Post by ilm
Hey, that's extremely interesting. I suppose a similar technique could
be used to "relay" any WM_DROPFILES message my window receives to a
window in another process? Any idea how that would look like?

How do you mean, other than making sure that DefWindowProc does not get a chance to free the HGLOBAL before it reaches the target?

Well I actually meant making a copy of the entire original message and
all its associated data.

[Jim Barry]

Post by ilm
Well I actually meant making a copy of the entire original message and
all its associated data.

There shouldn't be any need to copy the data, the HGLOBAL can just be passed on as-is.

- Jim

[unknown]

No it can't. Separate address spaces, y'know.

Post by ilm
Well I actually meant making a copy of the entire original message and
all its associated data.

There shouldn't be any need to copy the data, the HGLOBAL can just be passed
on as-is.

- Jim

[Henk Devos]

But in the specific case of HDROP, Windows handles this in some way and
copies the data to the other address space.

Post by unknown
No it can't. Separate address spaces, y'know.

Post by ilm
Well I actually meant making a copy of the entire original message and
all its associated data.

There shouldn't be any need to copy the data, the HGLOBAL can just be passed
on as-is.
- Jim

[Paul Baker]

I agree with Jim and Henk. You're thinking too much!

Paul

Post by Henk Devos
But in the specific case of HDROP, Windows handles this in some way and
copies the data to the other address space.

Post by unknown
No it can't. Separate address spaces, y'know.

Post by ilm
Well I actually meant making a copy of the entire original message and
all its associated data.

There shouldn't be any need to copy the data, the HGLOBAL can just be

passed

Post by unknown
on as-is.
- Jim

[Jim Barry]

Post by Henk Devos
But in the specific case of HDROP, Windows handles this in
some way and copies the data to the other address space.

Yes, exactly. (Well, not for HDROP generally, but for WM_DROPFILES in particular.) DoDragDrop would otherwise have great difficulty in delivering WM_DROPFILES messages to windows with WS_EX_ACCEPTFILES set. I must correct my earlier statement about freeing the handle - the destination process will receive a copy of the HGLOBAL, so the source process should free the original handle (i.e. call DragFinish) after forwarding it.

- Jim

[George]

This technique works for a lot applications, but not work for:
Window Media Player, RealOne Player;
Netscape, Internet Explorer;
Window Explorers.

Post by Jim Barry

Post by Joseph Scandura
We're trying to send a WM_DROPFILES message to MS
SoundRecorder.
We don't know exactly the format of the structure to send
as an HDROP parameter to the SendMessage (hWndSoundRec,
WM_DROPFILES, (WPARAM) &oMedium, 0L) function.
The message is actually recieved by the Sound Recorder.
"File cannot be opened" with random characters (indicating
reading from a non-allocated, or corrupted memory
location) at the end.

As Henk correctly points out, the WPARAM should be an HGLOBAL containing the DROPFILES structure. Try the following code snippet. It seems to be important to use PostMessage rather than SendMessage, I'm not too sure why that is.
int main(int argc, char* argv[])
{
if (HWND hwnd = FindWindow ("SoundRec", 0))
{
char filename[] = "c:\\temp\\test.wav";
if (HGLOBAL hGlobal =
GlobalAlloc(GHND, sizeof(DROPFILES) + strlen(filename) + 2))
{
DROPFILES * df = static_cast<DROPFILES *>(GlobalLock(hGlobal));
df->pFiles = sizeof(DROPFILES);
strcpy(reinterpret_cast<char *>(df + 1), filename);
GlobalUnlock(hGlobal);
if (!PostMessage(hwnd, WM_DROPFILES, (WPARAM)hGlobal, 0))
GlobalFree(hGlobal);
}
}
return 0;
}

[Jim Barry]

Post by George
Window Media Player, RealOne Player;
Netscape, Internet Explorer;
Window Explorers.

That will be because these applications do not actually handle the WM_DROPFILES message. Instead, they implement IDropTarget and call RegisterDragDrop. Unfortunately, there is currently no documented method of retrieving the IDropTarget interface associated with a window.

- Jim

[a***@discussions.microsoft.com]

Thanks a lot guys, we got it fixed.