Code:
UpdateWindow(handle);
Code:
UpdateWindow
The UpdateWindow function updates the client area of the specified window by sending a WM_PAINT message to the window if the window's update region is not empty. The function sends a WM_PAINT message directly to the window procedure of the specified window, bypassing the application queue. If the update region is empty, no message is sent. 

BOOL UpdateWindow(
  HWND hWnd   // handle of window
);
 
Parameters
hWnd 
Handle to the window to be updated. 
Return Values
If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero.