Windows8编程Metro App的一个自定义模态对话框控件。我们知道MessageDialog不能自定义UI，而Metro的Popup控件是非模态的，所以只能自定义模态对话框。-This is a modal popup for Win8 metro app. We known that MessageDialog can t defined UI, and Metro s Popup control is not a modal popup. so, we need to defined