1. 有时候，会显示“正在恢复”，并等待时间较长，才能回到用户切出时候的画面，但是这种情况并非常见，偶尔发生
2. 有时候，直接回到切出时的画面，反应还蛮迅速的
   

1. 用户点击WIN键
2. 发送短信，跳往WIFI设置，或者其他Task

切出应用后，会触发事件Deactivated，失活，也就是不在前台显示了

然后，

这里是关键

存在两个状态

1. Dormant
2. TomeStoned

Dormant

When the user navigates forward, away from an app, after the Deactivated event is raised, 
the operating system will attempt to put the app into a dormant state. 
In this state, all of the application’s threads are stopped and no processing takes place, 
but the application remains intact in memory. If the app is reactivated from the dormant, 
it doesn’t need to do anything to re-establish state, because it has been preserved.

If new apps are launched after an app has been made dormant, 
and these applications requires more memory than is available to provide a good user experience, 
the operating system will begin to tombstone dormant applications to free up memory.

休眠

Tombstoned

A tombstoned app has been terminated, but the operating system preserves information about its navigation state 
and also preserves the state dictionaries the app populated during Deactivated. 
The device will maintain tombstoning information for up to five apps at a time. 
If an app is tombstoned and the user navigates back to the application, 
it will be relaunched and the application can use the preserved data to restore state.

1. 有时候，会显示“正在恢复”，并等待时间较长，才能回到用户切出时候的画面，但是这种情况并非常见，偶尔发生
2. 有时候，直接回到切出时的画面，反应还蛮迅速的

我认为，

这是因为两种不同的状态返回了应用而致：

应用是从休眠状态重新激活的，则无需执行任何操作来重建状态，因为状态已被保留。

于是这样发生了2