活动：应用程序中的单个屏幕提供用户界面。 对于一个应用程序来说可以有若干个活动，启动是提供给用户的活动叫做主要活动。 -Activities: The application provides a single-screen user interface. For an application, it can have several activities, start-up is provided to the user activity is called the primary a