采用3种方式（OnPaint()、OnEraseBkgnd()、OnCtlColor()）实现对对话框背景的改写，并且比较3种方式的优缺点及三个函数的执行顺序。-With 3 ways (OnPaint (), OnEraseBkgnd (), OnCtlColor ()) to achieve the background of the dialog box rewritten, and compare the advantages and disadvantages of 3 ways th