Thread: SetClassLong changes are delayed

I have this code to change the background of a window:

Code:

			HBRUSH hBrush = NULL;
			switch(LOWORD(wParam))
			{

				//
				// ... some other stuff ...
				//

				case IDM_RED: hBrush = ::CreateSolidBrush(RGB(0xFF, 0x00, 0x00)); break;
				case IDM_YELLOW: hBrush = ::CreateSolidBrush(RGB(0xFF, 0xFF, 0x00)); break;
				case IDM_BLACK: hBrush = ::CreateSolidBrush(RGB(0x00, 0x00, 0x00)); break;
				case IDM_WHITE: hBrush = ::CreateSolidBrush(RGB(0xFF, 0xFF, 0xFF)); break;
				case IDM_GREEN: hBrush = ::CreateSolidBrush(RGB(0x00, 0xFF, 0x00)); break;
				case IDM_BLUE: hBrush = ::CreateSolidBrush(RGB(0x00, 0x00, 0xFF)); break;
			}
			if(hBrush)
			{
				::SetClassLong(hwnd, GCL_HBRBACKGROUND, (long) hBrush);
			}

However, the background color only changes when I go away and come back to the window. MSDN warned of this sort of thing like delayed repainting or something, but I was not sure of a remedy. Also, it says that this function was superceded by SetClassLongPtr(..) but when I tried to use it it said it was undeclared even when I put

Code:

#define _WIN32_WINNT 0x501
#include <windows.h>

Any ideas for that?

That works, thank you. Why it is not working is probably because I have VC6

I have one more small related question related to the deletion of these brushes. MSDN says:

Originally Posted by MSDN

The system automatically deletes class background brushes when the class is unregistered by using UnregisterClass. An application should not delete these brushes.

If I am replacing these brushes one by another changing the color of the background, should I be applying DeleteObject(..) to them as I recieve them from the return of SetClassLong?

>> I take it your intention is to affect all windows of a specific window class, which SetClassLong/Ptr will do, rather than just a specific window?

Not necessarily, but it just so happens that I only have one window of that class. I might look into something like ::FillRect(..) on the client area instead I guess. Thank you for the help.

Okay. I now am experiencing trouble which I has something to do with device-contexts and confuses me. I now am using FillRect to paint the window, and unfortunently now whenever it encounters a repaint, it repaints it the default class color instead of remembering what I have done to the DC. Here is the code:

Code:

				if(hBrush)
				{
					HDC hDC = ::GetDC(hwnd);
					RECT cR;
					
					::GetClientRect(hwnd, &cR);
					::FillRect(hDC, &cR, hBrush);
					

					::DeleteObject(hBrush);
					::ReleaseDC(hwnd, hDC);
				}

Could I get any advice or some buzzwords?

The background painting using the class brush is done in the handling of WM_ERASEBKGND by DefWindowProc. This means that you should either you a class background brush of NULL (in which case no background painting will be done by DefWindowProc) or override the WM_ERASEBKGND message and do your own background painting.