How to resize window using WinAPI

Question

I'm want resize window using WinAPI. I use WinAPI function

SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int x, int y, int cx, int cy, uint uFlags);

Window is resized, but window content is not redrawed. If I resize this window using mouse, content redraws. How to resize window using WinAPI with content redrawing?

Answer 1

Make sure you don't specify SWP_NOREDRAW in the uFlags parameter. If it's not set and you still get the problem, just call UpdateWindow(hwnd) manually.

Answer 2

By default the window is not redrawn (more precisely - not invalidated) upon resize. If you shrink the window - it won't receive the WM_PAINT at all. And if you enlarge it - the update region will only include the added area.

If the contents of the window depend on its size - the window itself must decide to invalidate itself (via a call to InvalidateRect/InvalidateRgn) upon processing WM_SIZE message.

Nevertheless you can invalidate any window at any time by calling InvalidateRect/InvalidateRgn.