No result code for SendMessage with WM_COPYDATA

[Guest]

Hello,
I try a inter process communication with windows messages and WM_COPYDATA.
It should work for managed and unmanaged applications. The receiver of
WM_COPYDATA messages is a managed applications. For the sender the result
code of SendMessage is important.
In the managed receiver I use Microsoft.WindowsCE.Forms.MessageWindow. I
override the WndProc, to check for WM_COPYDATA. Then I set the msg.Result to
the desired value and call base.WndProc. But the sender always get 0 as
result of his SendMessage.
What's wrong? Does base.WndProc overwrite my msg.Result.
Here is a code snippet from my receiver.

protected override void WndProc(ref Message msg)
{
switch(msg.Msg)
{
case Const.WM_COPYDATA:
COPYDATASTRUCT st = (COPYDATASTRUCT)
Marshal.PtrToStructure(msg.LParam, typeof(COPYDATASTRUCT));
if (this.iCallback != null)
{
string data = Marshal.PtrToStringUni(st.lpData);
msg.Result = AnotherFunction(data);
}
break;
}
base.WndProc (ref msg);
}

Thanks in advance
Steffen

 

[Guest]

You're certain the sender has the right hWnd for the MessageWindow?

-Chris

 

[Guest]

Hi Chris,
yes, I think so. He gets the hWnd with FindWindow(NULL, ReceiverWindowName)
and the receiver sets the window title with SetWindowText. He also needs the
hWnd, becaues he uses SendMessage with hWnd parameter set and not with
broadcast message.
Now I also have a unmanaged sender application, with same result (0) for
SendMessage.

By Steffen

 

[Chris Tacke, MVP]

What does GetLastError return after the fail?

-Chris

 

[Guest]

Hi Chris,

What does GetLastError return after the fail?

the SendMessage function doesn't reply any error code, only 0. If I call
GetLastError immediatly after SendMessage I get for the first call code 57
and then 6, which is ERROR_INVALID_HANDLE. But I can't believe, that I'm
using wrong handle. I've checked all window handle with Remote Spy and get
the same values, I'm using. And the message reach their destination.
Then I made a test to call SendMessage from managed to unmanaged
application. In unmanaged application WindowProc returns a value. In managed
application I'll get this value back. I made also some test with a WM_USER
message, but he same result.

I think, that somebody changes the msg.Result in
Microsoft.WindowsCE.Forms.MessageWindow.WndProc(ref Msg), when I call
base.WndProc.

By
Steffen

 

[Guest]

Hello again,
I've done a test with full framework with same result. So I think, I'm doing
something wrong. Who can figure out my error.
Here is the code from two simple WinForm applications,

Form1 overwritten WndProc
protected override void WndProc(ref Message m)
{
if (m.Msg == WM_USER)
{
m.Result = (IntPtr) 10;
}
base.WndProc (ref m);
}

Form2 gets the hWnd from Form1 with FindWindow and sends a WM_USER message.
the result is always 0.
private void button1_Click(object sender, System.EventArgs e)
{
IntPtr hwnd = FindWindow(IntPtr.Zero,"Form1");
if (hwnd != IntPtr.Zero)
{
int result = SendMessage(hwnd,WM_USER,0,0);
this.textBox1.Text = result.ToString();
}
}

Thanks
Steffen

 

[Guest]

Hello
the problem is solved.
If I do not call base.WndProc for messages I handle in derived class
WndProc, everything works.
Steffen