Re: writing to gui from thread

From:
Norbert Unterberg <nunterberg@newsgroups.nospam>
Newsgroups:
microsoft.public.vc.mfc
Date:
Mon, 19 Feb 2007 22:23:15 +0100
Message-ID:
<OL8ZswGVHHA.5068@TK2MSFTNGP03.phx.gbl>
kunal s patel schrieb:

Now when someone press a button in maindlg application i spawn a thread
like this:

UINT MyThread(LPVOID obj)
{
    sim s;
    s.proc();
}

The function proc is defined as

void sim::proc()
{
   Cmaindlg* pmain = (Cmaindlg*) AfxGetMainWnd();
   pmain->m_listbox.AddString("Hi");
}

Now when i try to run this application, i get an assertion error. I am not
able to understand what is going wrong. Can anyone explain me the way out of
it. Basically i want to access the gui objects from thread.


MFC window objects can only be used in the same thread that created them. Since
the m_listbox was created by the main GUI thread it can not be used from another
thread.

In addition, doing user interaction from a thread is a bad idea and opens the
door to all kind of bugs and problems. The assert you hit is only one of them.
Your worker thread should post (not send) a message to the main thread telling
it to add the string to the list box.

Norbert

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