CODEWITHSUNDEEP
cwinapi
user4344762
user4344762

Reputation:

Does InvalidateRect() sends WM_PAINT messages to the child controls?

If I called InvalidateRect() on the parent Window, for example:

InvalidateRect(hWnd, NULL, TRUE);

What will happen is that inside the WM_PAINT handler, BeginPaint() will send a WM_ERASEBKGND message, which will erase the background, and hence all child controls will disappear.

But the child controls remain when I call InvalidateRect(), so does that means InvalidateRect() also sends WM_PAINT messages to the child controls also?

Upvotes: 1

Views: 1771

Answers (1)

marcinj
marcinj

Reputation: 50046

Does InvalidateRect() sends WM_PAINT messages to the child controls?

yes (mostly), its quite clearly described here:

https://msdn.microsoft.com/en-us/library/windows/desktop/dd183426(v=vs.85).aspx

The system sets the update region for a child window whenever part of the parent window's update region includes a portion of the child window. In such cases, the system first sends a WM_PAINT message to the parent window and then sends a message to the child window, allowing the child to restore any portions of the window that the parent may have drawn over.

but with exception:

an application cannot generate a WM_PAINT message for the child by invalidating a portion of the parent's client area that lies entirely under the child window. In such cases, neither window receives a WM_PAINT message.

which is actually interesting to know

You can prevent redraw of child windows by setting WS_CLIPCHILDREN to parent window, or by invalidating redraw with the use of RedrawWindow function with RDW_NOCHILDREN flag.

Upvotes: 1

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