在WM_GETMINMAXINFO消息中这样设置
lpMMI-> ptMaxSize.x = GetSystemMetrics(SM_CXFULLSCREEN) + GetSystemMetrics(SM_CXDLGFRAME);
lpMMI-> ptMaxSize.y = GetSystemMetrics(SM_CYFULLSCREEN) + GetSystemMetrics(SM_CYCAPTION) + GetSystemMetrics(SM_CYDLGFRAME);
参照
http://topic.youkuaiyun.com/t/20060626/11/4843051.html