Why OnPaint() is continously calling while debugging

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Hi,

when I debug an MFC application and if I put a break point in OnPaint().This

function continously calling while debugging.My doubt is that it is happening only

while i am debugging the code.

Thanks in advance

Posted 24-Nov-11 0:01am

kutz 2

Updated 26-May-20 22:32pm

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4 solutions

Solution 1

This is because your application is hitting a break point Visual Studio is firing up and repainting the screen you step through your code and your application window gets focused again and needs a repaint.

Try bringing up your application and Visual Studio side by side (non overlapping windows).

Posted 24-Nov-11 0:08am

Mehdi Gholam

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kutz 2 24-Nov-11 8:07am

If I put a message box in that function(OnPaint()) and build it in debug mode or release mode.Then i run the application it will show the message box only at one time.Please note that the above case(My question) is not happening with visual studio 2010

Solution 4

You might have some endless loop in your "onPaint" function, such that you always set some value which calls "Invalidate" which will cause an "onPaint" call.

If that's the case you can register to the "Invalidated" event, and add there a breakPoint.

I'm using 2 screens, so the debugger doesn't cause WM_PAINT to be called, and the above helped me to find the stackTrace which caused the endless "onPaint".

Posted 26-May-20 22:33pm

Member 11211791

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CPallini · Accepted Answer · 2011-11-24T00:09:00

Solution 2

It's normal: it happens beacuse the debugger window overlaps the 'painted one' (and then the latter overlaps the debugger window itself) hence making the system generating new WM_PAINT messages.

Posted 24-Nov-11 0:09am

CPallini

Updated 24-Nov-11 0:10am

v2

Pranit Kothari · Accepted Answer · 2011-11-24T00:26:00

Any time your window gets overlapped with another window, minimized, maximized or re-size WM_PAINT message is sent to your application by Operating System, and its handler ONPaint() gets called. While debugging your may be encounter with any of these situations.

This[^]is very useful article for analyzing your problem.

Regards