Re: howto avoid cdc drawing done not in onPaint to be erased?

David Wilkinson <>
Wed, 11 Jul 2007 04:44:40 -0500
Equilibrium wrote:

hi all,
I have a static control in which i want to draw a circle.
I have subclassed the static control to a "CMyStatic" class.
added a CDC member -> CDC * pDC;
Initialize this member in OnMove function ->
void CMyStatic::OnMove(int x, int y)
    CStatic::OnMove(x, y);

    pDC = GetDC();
draw an ellipse on mouse click ->
void CMyStatic::OnLButtonDown(UINT nFlags, CPoint point)
        pDC->Ellipse(0,0,100,100) ;

    CStatic::OnLButtonDown(nFlags, point);

and ran the application.

everything was great till I'ved minimize , or covered the dialog , the
drawing disappeard.
I know i need to do something regurding MemDC ' but i can't find any

The goal is to draw items dinamically with the mouse or any other
place rather that the OnPaint function/


For the reason you have noted, all drawing code must be in
OnPaint/OnDraw. If you want it somewhere else, it must be duplicated,
preferably by calling a common function from both places.

But the usual way to update the drawing is to call Invalidate() or
InvalidateRect(), possibly followed by UpdateWindow(). Why do you not
want to do this?

David Wilkinson
Visual C++ MVP

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