Since this is a Silverlight for Windows Phone application, you need to follow the Silverlight programming model and define your user interface using XAML.
Figure 6 Creating and saving a new Windows Phone application project in Microsoft Visual Studio 2010
Figure 5 Creating a new Windows Phone application project in Microsoft Visual Studio 2010 Express for Windows Phone
注意是不一样的visual studio 2010版本啊！
打开App.xaml可以看到以Application为根的XAML文档，里面包含了Application.Resource,更是初始化了RootVisual属性来定义程序的第一个page
App.xaml和App.xaml.cs定义了Application类的一个实例，这个Application类封装了对应于windows phone的Silverlight并且提供了程序的入口点
MainPage.xaml定义了程序的主要UI
Task 5 – Managing Errors in the Application
待续