Problem in sending WM_COPYDATA message
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Peter S. Le
#1 / 7
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 Problem in sending WM_COPYDATA message I am trying to make two applications comunicate with each other.. In one application (let's call it A), I use "FindWindow" function to get the
handle of the other application (B).
B application is the dialog based application with the window text "AAA."
In A:
HWND hWnd = FindWindow ("#32770", "AAA");
-> The resulting hWnd is not NULL.. so..
SendMessage (hWnd, WM_COPYDATA, (WPARAM)thisHwnd, (LPARAM)data);
-> Also, it works..
In B application, however, the handler of WM_COPYDATA that is OnCopyData
(..) is not called..
WHEN I changed SendMessage like following..
SendMessage (HWND_BROADCAST, WM_COPYDATA, ...);
the OnCopyData function is called..
I can't find anything wrong in my program..
Can anybody help me?
ANY helps or comments would be appriciated..
Peter S. Lee
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| Sun, 14 Dec 2003 18:05:22 GMT |
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James Pannozz
#2 / 7
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Problem in sending WM_COPYDATA message There is a known bug using OnCopyData. Use ON_MESSAGE Using Broadcast is bad, see note below. Jim See following earlier post found from Deja.
ON_MESSAGE(WM_COPYDATA, OnCopyData)
LRESULT CMyWnd::OnCopyData( WPARAM wParam, LPARAM lParam )
{
CWnd* pWndSender = CWnd::FromHandle((HWND)wParam);
COPYDATASTRUCT* pcds = (COPYDATASTRUCT*) lParam;
/* Do your work here */
return TRUE; // handled
}
Note: WM_COPYDATA can be broadcasted over top-level windows,
it is a very bad idea to ignore the sender window because
you can analyze an unknown COPYDATASTRUCT. I do not understand
why the WM_COPYDATA can be broadcasted, it
would be IMHO strictly forbidden !
Submitted By: Stphane Gibier (1999/07/02)
Quote: > I am trying to make two applications comunicate with each other.. > In one application (let's call it A), I use "FindWindow" function to get
the
> handle of the other application (B).
> B application is the dialog based application with the window text "AAA."
> In A:
> HWND hWnd = FindWindow ("#32770", "AAA");
> -> The resulting hWnd is not NULL.. so..
> SendMessage (hWnd, WM_COPYDATA, (WPARAM)thisHwnd, (LPARAM)data);
> -> Also, it works..
> In B application, however, the handler of WM_COPYDATA that is OnCopyData
> (..) is not called..
> WHEN I changed SendMessage like following..
> SendMessage (HWND_BROADCAST, WM_COPYDATA, ...);
> the OnCopyData function is called..
> I can't find anything wrong in my program..
> Can anybody help me?
> ANY helps or comments would be appriciated..
> Peter S. Lee
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| Sun, 14 Dec 2003 21:45:10 GMT |
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Sam Hobb
#3 / 7
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Problem in sending WM_COPYDATA message There might be something obvious that more experienced Windows developers are aware of but if it were me I would use Spy++ to diagnose the problem if I cannot diagnose it using something easier. And Spy++ is relatively easy to use. I think I would put a TRACE after FindWindow to show hWnd in hex format and I would use SPY++ to determine what the handle is for the dialog. If the two do not agree then I would have something much more specific to diagnose. The SendMessage with the correct handle should work and probably you are not getting the correct handle for some reason.
Quote: > I am trying to make two applications comunicate with each other.. > In one application (let's call it A), I use "FindWindow" function to get
the
> handle of the other application (B).
> B application is the dialog based application with the window text "AAA."
> In A:
> HWND hWnd = FindWindow ("#32770", "AAA");
> -> The resulting hWnd is not NULL.. so..
> SendMessage (hWnd, WM_COPYDATA, (WPARAM)thisHwnd, (LPARAM)data);
> -> Also, it works..
> In B application, however, the handler of WM_COPYDATA that is OnCopyData
> (..) is not called..
> WHEN I changed SendMessage like following..
> SendMessage (HWND_BROADCAST, WM_COPYDATA, ...);
> the OnCopyData function is called..
> I can't find anything wrong in my program..
> Can anybody help me?
> ANY helps or comments would be appriciated..
> Peter S. Lee
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| Sun, 14 Dec 2003 22:29:46 GMT |
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Peter S. Le
#4 / 7
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Problem in sending WM_COPYDATA message Thanks.. But I also tried ON_MESSAGE..
It didnot work, either.. 8(
Peter.
Quote: > There is a known bug using OnCopyData. > Use ON_MESSAGE > Using Broadcast is bad, see note below. > Jim > See following earlier post found from Deja.
> ON_MESSAGE(WM_COPYDATA, OnCopyData)
> LRESULT CMyWnd::OnCopyData( WPARAM wParam, LPARAM lParam )
> {
> CWnd* pWndSender = CWnd::FromHandle((HWND)wParam);
> COPYDATASTRUCT* pcds = (COPYDATASTRUCT*) lParam;
> /* Do your work here */
> return TRUE; // handled
> }
> Note: WM_COPYDATA can be broadcasted over top-level windows,
> it is a very bad idea to ignore the sender window because
> you can analyze an unknown COPYDATASTRUCT. I do not
understand
> why the WM_COPYDATA can be broadcasted, it
> would be IMHO strictly forbidden !
> Submitted By: St?hane Gibier (1999/07/02)
> > I am trying to make two applications comunicate with each other..
> > In one application (let's call it A), I use "FindWindow" function to get
> the
> > handle of the other application (B).
> > B application is the dialog based application with the window text
"AAA."
> > In A:
> > HWND hWnd = FindWindow ("#32770", "AAA");
> > -> The resulting hWnd is not NULL.. so..
> > SendMessage (hWnd, WM_COPYDATA, (WPARAM)thisHwnd, (LPARAM)data);
> > -> Also, it works..
> > In B application, however, the handler of WM_COPYDATA that is OnCopyData
> > (..) is not called..
> > WHEN I changed SendMessage like following..
> > SendMessage (HWND_BROADCAST, WM_COPYDATA, ...);
> > the OnCopyData function is called..
> > I can't find anything wrong in my program..
> > Can anybody help me?
> > ANY helps or comments would be appriciated..
> > Peter S. Lee
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| Mon, 15 Dec 2003 08:26:51 GMT |
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Peter S. Le
#5 / 7
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Problem in sending WM_COPYDATA message Thanks.. I see that the problem is disagreement of two hWnd values..
What can I diagnose further?
The hWnd value of FindWindow is not NULL..
Does this mean that it finds the correct window of "AAA" ?
I thought that if I wrote wrong window class name or window title as
arguments of FindWindow,
the hWnd value of FindWindow should be NULL..
Am I wrong?
Please, help me..
Peter.
Quote: > There might be something obvious that more experienced Windows developers > are aware of but if it were me I would use Spy++ to diagnose the problem if > I cannot diagnose it using something easier. And Spy++ is relatively easy to > use. I think I would put a TRACE after FindWindow to show hWnd in hex format > and I would use SPY++ to determine what the handle is for the dialog. If the > two do not agree then I would have something much more specific to diagnose. > The SendMessage with the correct handle should work and probably you are not > getting the correct handle for some reason.
> > I am trying to make two applications comunicate with each other..
> > In one application (let's call it A), I use "FindWindow" function to get
> the
> > handle of the other application (B).
> > B application is the dialog based application with the window text
"AAA."
> > In A:
> > HWND hWnd = FindWindow ("#32770", "AAA");
> > -> The resulting hWnd is not NULL.. so..
> > SendMessage (hWnd, WM_COPYDATA, (WPARAM)thisHwnd, (LPARAM)data);
> > -> Also, it works..
> > In B application, however, the handler of WM_COPYDATA that is OnCopyData
> > (..) is not called..
> > WHEN I changed SendMessage like following..
> > SendMessage (HWND_BROADCAST, WM_COPYDATA, ...);
> > the OnCopyData function is called..
> > I can't find anything wrong in my program..
> > Can anybody help me?
> > ANY helps or comments would be appriciated..
> > Peter S. Lee
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| Mon, 15 Dec 2003 08:31:51 GMT |
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Sam Hobb
#6 / 7
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Problem in sending WM_COPYDATA message Are you sure that FindWindow returns a valid handle? You could use Spy++ to validate the handle. Validate that the window caption and class matches what you expect. I wonder if it is possible you are calling CWnd::FindWindow, which returns
CWnd*, instead of ::FindWindow, which returns HWND. I have not heard of that
happening so I suppose it would not. If, however, you are using a cast for
the return value from FindWindow because the compile complains without it,
then you must take a real close look at that.
Otherwise it seems that the only other possibility is that you have more
than one window with the same class and window name. You could write
something to check that out but hopefully you can use Spy++ to check that
out.
Quote: > Thanks.. > I see that the problem is disagreement of two hWnd values..
> What can I diagnose further?
> The hWnd value of FindWindow is not NULL..
> Does this mean that it finds the correct window of "AAA" ?
> I thought that if I wrote wrong window class name or window title as
> arguments of FindWindow,
> the hWnd value of FindWindow should be NULL..
> Am I wrong?
> Please, help me..
> Peter.
> > There might be something obvious that more experienced Windows
developers
> > are aware of but if it were me I would use Spy++ to diagnose the problem
> if
> > I cannot diagnose it using something easier. And Spy++ is relatively
easy
> to
> > use. I think I would put a TRACE after FindWindow to show hWnd in hex
> format
> > and I would use SPY++ to determine what the handle is for the dialog. If
> the
> > two do not agree then I would have something much more specific to
> diagnose.
> > The SendMessage with the correct handle should work and probably you are
> not
> > getting the correct handle for some reason.
> > > I am trying to make two applications comunicate with each other..
> > > In one application (let's call it A), I use "FindWindow" function to
get
> > the
> > > handle of the other application (B).
> > > B application is the dialog based application with the window text
> "AAA."
> > > In A:
> > > HWND hWnd = FindWindow ("#32770", "AAA");
> > > -> The resulting hWnd is not NULL.. so..
> > > SendMessage (hWnd, WM_COPYDATA, (WPARAM)thisHwnd, (LPARAM)data);
> > > -> Also, it works..
> > > In B application, however, the handler of WM_COPYDATA that is
OnCopyData
> > > (..) is not called..
> > > WHEN I changed SendMessage like following..
> > > SendMessage (HWND_BROADCAST, WM_COPYDATA, ...);
> > > the OnCopyData function is called..
> > > I can't find anything wrong in my program..
> > > Can anybody help me?
> > > ANY helps or comments would be appriciated..
> > > Peter S. Lee
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| Mon, 15 Dec 2003 10:13:15 GMT |
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Joseph M. Newcome
#7 / 7
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Problem in sending WM_COPYDATA message Did you put the ON_MESSAGE handler in the right window? You need to make sure that the window you think you are putting the handler in is the actual window that is the top-level window. You can do this by using Spy++ to identify the target window and its handle, and see if that value is the value you get back from FindWindow. In addition, you can then have Spy++ trace the messages to see if the window is receiving it. This may help pin down why the message appears to not be intercepted. I have been nailed several times by people who seem to have made the
same HWND_BROADCAST discovery. If you send WM_COPYDATA this way, then
EVERY window will receive it, including those which are expecting
WM_COPYDATA from "friends". What I do in my WM_COPYDATA handling is to
put a 128-bit GUID as the first 16 bytes of the message. When I
receive the message, I check that the GUID that appears in the first
16 bytes is the GUID my "friends" have agreed to put there; if I don't
see that GUID there, I ignore the message. This is critical, because
if you run in an environment where someone has done the HWND_BROADCAST
trick, you are dead meat.
Also, I find the use of "FindWindow" to be risky. When I have two
cooperating processes, I put a registered-window-message handler in
the target. I then do SendMessageTimeout of a Registered Window
Message (using a 200ms delay). The receiver responds to this message
by returning the same Registered Window Message value (it turns out
you can't rely on an unknown message returning 0, which is the defined
behavior of DefWindowProc, because Microsoft violates their own
specification and has some daemon components for Personal Web Server
that return 1 for every message, even messages they don't understand.
Stupid and irresponsible, but that's what it does. Microsoft
explicitly states in one of their design documents that (a) if you
don't understand a message, pass it to DefWindowProc and (b)
DefWindowProc will always return 0 for any message it doesn't
recognize). I find my method to be reliable, because it can be easily
internationalized. Depending on the contents of the window caption, or
the window class name, is far more risky (I once searched by window
class name, and got a window from a completely different application
that used the same window class name).
joe
On Thu, 28 Jun 2001 09:26:51 +0900, "Peter S. Lee"
Quote:
>Thanks.. >But I also tried ON_MESSAGE..
>It didnot work, either.. 8(
>Peter.
>> There is a known bug using OnCopyData.
>> Use ON_MESSAGE
>> Using Broadcast is bad, see note below.
>> Jim
>> See following earlier post found from Deja.
>> ON_MESSAGE(WM_COPYDATA, OnCopyData)
>> LRESULT CMyWnd::OnCopyData( WPARAM wParam, LPARAM lParam )
>> {
>> CWnd* pWndSender = CWnd::FromHandle((HWND)wParam);
>> COPYDATASTRUCT* pcds = (COPYDATASTRUCT*) lParam;
>> /* Do your work here */
>> return TRUE; // handled
>> }
>> Note: WM_COPYDATA can be broadcasted over top-level windows,
>> it is a very bad idea to ignore the sender window because
>> you can analyze an unknown COPYDATASTRUCT. I do not
>understand
>> why the WM_COPYDATA can be broadcasted, it
>> would be IMHO strictly forbidden !
>> Submitted By: St?hane Gibier (1999/07/02)
>> > I am trying to make two applications comunicate with each other..
>> > In one application (let's call it A), I use "FindWindow" function to get
>> the
>> > handle of the other application (B).
>> > B application is the dialog based application with the window text
>"AAA."
>> > In A:
>> > HWND hWnd = FindWindow ("#32770", "AAA");
>> > -> The resulting hWnd is not NULL.. so..
>> > SendMessage (hWnd, WM_COPYDATA, (WPARAM)thisHwnd, (LPARAM)data);
>> > -> Also, it works..
>> > In B application, however, the handler of WM_COPYDATA that is OnCopyData
>> > (..) is not called..
>> > WHEN I changed SendMessage like following..
>> > SendMessage (HWND_BROADCAST, WM_COPYDATA, ...);
>> > the OnCopyData function is called..
>> > I can't find anything wrong in my program..
>> > Can anybody help me?
>> > ANY helps or comments would be appriciated..
>> > Peter S. Lee
Joseph M. Newcomer [MVP]
Web: http://www3.pgh.net/~newcomer MVP Tips: http://www3.pgh.net/~newcomer/mvp_tips.htm
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| Tue, 16 Dec 2003 10:32:32 GMT |
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