Android-Overview Screen

学会使用Flag对Activity设置，然后可以更好的管理Activity 栈。

With the Android 5.0 release (API level 21), multiple instances of the same activity containing different documents may appear as tasks in the overview screen. 

Using the flags of the Intent class to add a task affords greater control over when and how a document gets opened or reopened in the overview screen. When you use the <activity> attributes you can choose between always opening the document in a new task or reusing an existing task for the document.

Activity：意图标签和Activity属性设置

Using the Intent flag to add a task。

Using the activity attribute to add a task。

 The  FLAG_ACTIVITY_NEW_DOCUMENT  flag replaces the  FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET  flag, which is deprecated as of Android 5.0 (API level 21).