App.xaml is the configuration of a bunch of parameters such as the start page, which is equivalent to the Main of the console program and the entrance of the whole program; For example:

& lt application x:Class="ViewControl. Application "

xmlns = "/winfx/2006/xaml/presentation "

xmlns:x="/winfx/2006/xaml "

startup uri = " main window . xaml " & gt；

& lt apply. Resources & gt

& lt/ application. Resources & gt

& lt/Application & gt；

The StartupUri here is where the start page is set.