Re: Update GUI in worker thread?
I would send a message to the GUI thread from the worker thread using
PostMessage() that tells it what to update. You can get the data from the
thread, but I wouldn't update the GUI from the thread. That's only asking
for problems. It's really easy to set up a custom message, assign the
window to a CWnd* variable in the thread, and post a message when there is
something new to update.
Be sure to call Sleep in your thread's loop when you don't need to be
processing so you give the rest of the program time to update as well.
Tom
"asm23" <asmwarrior@gmail.com> wrote in message
news:g82vtv$o74$1@aioe.org...
HI, My question is common&old in this forum. But I still get confused.
"In MFC, Can I update GUI in a worker thread?"
I cite some previous answers in this forum
*********************************************************************
someone says "NO"
"all the GUI related code, should be in the main thread."
said by Ajay in Apr 3 2007.
"The worker thread cannot directly access a window created in the main
thread. When you attempt to do that, in many cases MFC will assert
because it is an unsafe operation, not supported by MFC.
......
You should perform lengthy processing in your worker thread but not
attempt to access a main-thread window from the worker. Update the
window via PostMessage from the worker thread, as described in FAQ 11
and 12 here: http://www.mvps.org/vcfaq/mfc/index.htm"
said by Scott McPhillips.
***********************************************************************
someone says "Yes"
"It turns out that if you have a DC, you can render in multiple threads,
and there's even an MSDN example for concurrent rendering that was
cited. All other GUI interactions have to be kept in the main
thread,..."
said by Joshph.
"I know, an alternative way to solve this problem would
be to pass the worker thread a handle to the view window.
This method seems far more tricky, especially since both the
UI thread and the worker thread show data in the view window.
It would require a lot of synchronization to do this - ...."
said by someone.
*************************************************************************
In my application. A worker thread was created to capture image from a
digital camera continuously. I need to display captured image in
real-time( 100fps).
Here is my code in the worker thread:
//m_pwnd is a Pointer to a CWnd of primary thread.
while(1)
{
...
//wait Until data transfer completed.
//Prepare an image.
...
CDC* pdc= m_pwnd->GetDC();
CDC dcMem;
dcMem.CreateCompatibleDC(pdc);
CBitmap* pBmpOld = dcMem.SelectObject......
//select the CBitmap to the dcMem
pdc->BitBlt(......, &dcMem, ... SRCCOPY);
m_pwnd->ReleaseDC(pdc);
}
**********************************************************************
These code do works fine. But I don't know this is the recommended
strategy or best way.
Although I can put these GDI related code to primary thread, but it will
be more complex by data synchronization. Two situation could happen
simultaneously:
1.the image buffer is written by the worker thread.
2.the image buffer is used by primary thread to update CWnd.(on OnPaint
handler)
But things will be simple if I update CWnd in the worker thread, because I
needn't consider data synchronization.
Thank you for reading my post.
I'd be appreciate to hear your suggestion.