Activity启动模式

Activity 一共有四种启动模式。

用例	启动模式	多个实例？	描述
Normal launches for most activities	“standard”	Yes	Default. The system always creates a new instance of the activity in the target task and routes the intent to it.
	“singleTop”	Conditionally	If an instance of the activity already exists at the top of the target task, the system routes the intent to that instance through a call to its onNewIntent() method, rather than creating a new instance of the activity.
Specialized launches(not recommended for general use)	“singleTask”	No	The system creates the activity at the root of a new task and routes the intent to it. However, if an instance of the activity already exists, the system routes the intent to existing instance through a call to its onNewIntent() method, rather than creating a new one.
	“singleInstance”	No	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.

singleTask与singleInstance的区别：

The “singleTask” and “singleInstance” modes also differ from each other in only one respect: A “singleTask” activity allows other activities to be part of its task. It’s always at the root of its task, but other activities (necessarily “standard” and “singleTop” activities) can be launched into that task. A “singleInstance” activity, on the other hand, permits no other activities to be part of its task. It’s the only activity in the task. If it starts another activity, that activity is assigned to a different task — as if FLAG_ACTIVITY_NEW_TASK was in the intent.