Android : activity生命周期一点整理

生命周期的基本情况都是很清楚的,总结点可能容易忘记的点

1. onNewIntent
   大家遇到一个应用的Activity供多种方式调用启动的情况，多个调用希望只有一个Activity的实例存在，这就需要Activity的onNewIntent(Intent intent)方法了。只要在Activity中加入自己的onNewIntent(intent)的实现 加上Manifest中对Activity设置lanuchMode=“singleTask”就可以。

       onNewIntent（）非常好用，Activity第一启动的时候执行onCreate()---->onStart()---->onResume()等后续生命周期函数，也就时说第一次启动Activity并不会执行到onNewIntent(). 而后面如果再有想启动Activity的时候，那就是执行onNewIntent()---->onResart()------>onStart()----->onResume().  如果android系统由于内存不足把已存在Activity释放掉了，那么再次调用的时候会重新启动Activity即执行onCreate()---->onStart()---->onResume()等。

2. onPause
void android.app.Activity.onPause()
Called as part of the activity lifecycle when an activity is going into the background, but has not (yet) been killed. The counterpart to onResume.
When activity B is launched in front of activity A, this callback will be invoked on A. B will not be created until A's onPause returns, so be sure to not do anything lengthy here.
This callback is mostly used for saving any persistent state the activity is editing, to present a "edit in place" model to the user and making sure nothing is lost if there are not enough resources to start the new activity without first killing this one. This is also a good place to do things like stop animations and other things that consume a noticeable amount of CPU in order to make the switch to the next activity as fast as possible, or to close resources that are exclusive access such as the camera.
In situations where the system needs more memory it may kill paused processes to reclaim resources. Because of this, you should be sure that all of your state is saved by the time you return from this function. In general onSaveInstanceState is used to save per-instance state in the activity and this method is used to store global persistent data (in content providers, files, etc.)
After receiving this call you will usually receive a following call to onStop (after the next activity has been resumed and displayed), however in some cases there will be a direct call back to onResume without going through the stopped state.