MDIFrameBackground
代码说明：
To get this task done, my first instinct was to catch the WM_ERASEBKGND in CMainFrame and do the FillSolidRect there. But I soon realized that approach didn t do anything other than make the frame flicker and show red only when it s being resized, otherwise the gray background was completely intact. Not exactly what I was looking for. Suddenly it became a little mystery. Why doesn t the background of the frame change when I fill it with a color in the frame s WM_ERASEBKGND handler? So I went on a hunt, I went through a lot of the CMDIFrameWnd and CFrameWnd code looking for methods that would draw on the frame, and there was not much there. I finally ended up at CMainFrame::OnCreate method, I set a breakpoint and stepped through the CMDIFrameWnd::OnCreate method. After what seemed to be hours of searching I came across the following code in CMDIFrameWnd::CreateClient:
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