Android Activity launchMode

1. "standard" (the default mode)
   Default. The system creates a new instance of the activity in the task from which it was started and routes the intent to it. The activity can be instantiated multiple times, each instance can belong to different tasks, and one task can have multiple instances.

每一次都会重新创建一个实例

2. "singleTop"
   If an instance of the activity already exists at the top of the current 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. The activity can be instantiated multiple times, each instance can belong to different tasks, and one task can have multiple instances (but only if the activity at the top of the back stack is not an existing instance of the activity).For example, suppose a task's back stack consists of root activity A with activities B, C, and D on top (the stack is A-B-C-D; D is on top). An intent arrives for an activity of type D. If D has the default "standard" launch mode, a new instance of the class is launched and the stack becomes A-B-C-D-D. However, if D's launch mode is "singleTop", the existing instance of D receives the intent through onNewIntent(), because it's at the top of the stack—the stack remains A-B-C-D. However, if an intent arrives for an activity of type B, then a new instance of B is added to the stack, even if its launch mode is "singleTop".

简单来说就是: 处于堆栈的栈顶,并且不会重新实例化新的对象

3. "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.

不会重新实例化对象

4. "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.

类似于"singleTask",区别在于系统不会启动任何的activities放到这个任务堆栈中去处理这个实例.并且在这个被设置成"singleInstance"的Activity任务栈中只有他一个.由它启动的Activity都会被push到一个新的堆栈中.