您可以参考以下文档：

You can refer to following document:

http://msdn.microsoft.com/en-us/library/windows/apps/xaml/Hh868246 （v = win.10）.aspx

Alt键由 VirtualKey.Menu 值表示，但目前不支持此值使用C ++，C＃或Visual Basic的Metro风格应用程序。

The Alt key is represented by the VirtualKey.Menu value, but this value is not currently supported by Metro style apps using C++, C#, or Visual Basic.

***的问候，

Han Xia