CWindow::Invalidate
This method invalidates the entire client area and passes NULL for the RECT parameter to the InvalidateRect Windows CE function.
BOOL Invalidate(
BOOL bErase = TRUE);
Parameters
bErase Boolean that specifies whether the background within the update region is to be erased when the update region is processed. If this parameter is TRUE, the background is erased when the BeginPaint function is called. If this parameter is FALSE, the background remains unchanged.