C, win32: l need help with sendmessage function

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Please l need help on how i can send message to case WM_NOTIFY in my program. l want when a button is clicked(as in the case WM_COMMAND below), the SendMessage function activates case WM_NOTIFY so that the codes inside the WM_NOTIFY case will run.
l had tried my best but l only get unhandled exception error messages.
snippet below;

C++

case WM_COMMAND:
		wmId    = LOWORD(wParam);
		wmEvent = HIWORD(wParam);
		// Parse the menu selections:
		switch (wmId)
		{
		case IDC_NEXTBTN:
			QueNo++;
			SendMessage(hWnd,WM_NOTIFY,(int)IDC_NEXTBTN,(NMHDR)lParam);//here l cast wparam to int and wparam to (NMHDR) according to msdn for WM_NOTIFY
			break;
......

while in WM_NOTIFY, i have

C++

case WM_NOTIFY:
		{
		
		if(lpnmhdr->code==TCN_SELCHANGE||lpnmhdr->hwndFrom==NextBtn){
			
.....
}

Or is there any other way l can implement it.
Thanks everyone

What I have tried:

C

SendMessage(hWnd,WM_NOTIFY,(int)IDC_NEXTBTN,(NMHDR)lParam)

Posted 21-Feb-16 1:36am

Member 12139442

Updated 21-Feb-16 11:20am

CHill60

v2

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Comments

Richard MacCutchan 21-Feb-16 7:43am

And what happens?

Member 12139442 21-Feb-16 8:00am

It doesn't work and VC++ breaks at the if statement line and gives me unhandled exception.

Richard MacCutchan 21-Feb-16 8:18am

Probably because you are casting one object to another unrelated type. You cannot cast the lparam sent to WM_COMMAND to a NMHDR structure. You need to create a proper header structure and populate its member variables before passing it in to the notify code.

Kornfeld Eliyahu Peter 21-Feb-16 7:47am

It seems that your params are invalid...
The first should ahve the control id of the event source, and the second a structure of NMHDR...While the low word of wParam may(!) be the control id lParam never will be a NMHDR structure...but zero or window handle...

Member 12139442 21-Feb-16 8:01am

I also had tried parsing the window handled as well as 0, but no avail. VC++ breaks at the if statement line and gives me unhandled exception.

Kornfeld Eliyahu Peter 21-Feb-16 8:04am

Check the sample here: https://msdn.microsoft.com/en-us/library/windows/desktop/bb775583(v=vs.85).aspx

Member 12139442 21-Feb-16 17:10pm

Thanks. You saved me.

2 solutions

Solution 1

Quote:
the SendMessage function activates case WM_NOTIFY so that the codes inside the WM_NOTIFY case will run.

I won't do that. Instead I would factor out 'the code inside the WM_NOTIFY case' as a function and call directly such a function.

Posted 21-Feb-16 10:13am

CPallini

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Member 12139442 · Accepted Answer · 2016-02-21T11:20:00

C#

case WM_COMMAND:
		wmId    = LOWORD(wParam);
		wmEvent = HIWORD(wParam);
		// Parse the menu selections:
		switch (wmId)
		{
		case IDC_NEXTBTN:
			QueNo++;
			NMHDR nmh;
			nmh.code = NM_CLICK;    // Message type defined by control.
			nmh.idFrom =IDC_NEXTBTN;
			nmh.hwndFrom = NextBtn;
			SendMessage(GetParent(NextBtn),	WM_NOTIFY, nmh.idFrom, (LPARAM)&nmh);
			
			break;

Based on the link given by Konfeld.
And many thanks to all of you who contributed.
@CPallini: l would have but it wouldn't be much better than as l wanted.