launchMode中singleTask和singleInstance的区别

"singleTask"

The system creates a new task and instantiates the activity at the root of the new task. However, if an instance of the activity already exists in a separate task, the system routes the intent to the existing instance through a call to its onNewIntent() method, rather than creating a new instance. Only one instance of the activity can exist at a time.

Note: Although the activity starts in a new task, theBack button still returns the user to the previous activity.

译：

singleTask：当某个activityA声明的launchMode为singleTask时，会新开一个队列，activityA作为根，也就是第一个。但是，如果这个activityA已经存在于某个特殊的队列中，这时候就会把activity作为队顶，前面的都清除。

如：

activityA-》activityB->activityC->activityA的话，就会使队列只有一个activityA。

"singleInstance".

Same as "singleTask", except that the system doesn't launch any other activities into the task holding the instance. The activity is always the single and only member of its task; any activities started by this one open in a separate task.

译：

singleInstance和singleTask基本一样，除了不会把其它的activity放到这个唯一的队列里来，也就是说这个队列里永远只有一个。

如有三个Activity：

MainActivity (singleInstance) ActivityA(standard), ActivityB(standard)

MainActivity-》ActivityA-》ActivityB->MainActivity，这时如果再跳到ActivityA，会跳不过去，直接跳到ActivityB,相当于把整个taskB给提到MainActivity的task前面。

这时候是两个task之间的关系