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Worker thread and AfxGetMainWnd

Posted on 2004-09-19
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Last Modified: 2013-11-20
I have the following piece of code:

CWnd *CMyApp::GetView()
{
  CMainFrame *pFrm = (CMainFrame *)AfxGetMainWnd();
  return pFrm->GetActiveView();
}

It works fine from the main thread of the application. For some reason, I cannot call this function from a worker thread.

I have heard there is a problem when AfxGetMainWnd is called from a worker thread. Is this correct, and if so, why and what kind of problems?
 
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Question by:Lescha
3 Comments
 
LVL 48

Accepted Solution

by:
AlexFM earned 200 total points
ID: 12095133
You can read more about this problem here:

http://support.microsoft.com/default.aspx?scid=kb;EN-US;147578

CWnd-derived objects may be used only in the thread where they was created. Don't call directly any function of CWnd-derived class from the worker thread. Intead of this post user-defined message to the window.
Check out MFC sample MTRECALC.
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LVL 55

Expert Comment

by:Jaime Olivares
ID: 12097101
Still you can send standard window messages if you want to communicate with a view.
Something like:

theApp.m_pMainWnd->SendMessage(WM_USER+1, somedata, somedata);
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LVL 1

Author Comment

by:Lescha
ID: 12099681
The problem was that I forgot to create the thread as suspended, set its Main Window pointer, and then resume.
Still, it would be unfair to deny the answer points to Alex.
James - just for the record, SendMessage in the way you suggested crashes the application in Release mode. Dunno why.
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