关于android状态保存 onSaveInstanceState

      写了一年的安卓程序，第一次写博客，如是你看到勿喷。不是大神，只是热爱。

     关于安卓的状态保存的意义不累赘，

     只分享状态的保存的 使用的一些细节注意事项：

onSaveInstanceState的执行时间和执行条件

             1，执行条件，

     * Called to retrieve per-instance state from an activity before being killed

     * so that the state can be restored in {@link #onCreate} or

     * {@link #onRestoreInstanceState} (the {@link Bundle} populated by this   method

     * will be passed to both).

       保存状态在被杀死之前，为了这个状态被回复在onCreate和onRestoreInstanceState的方法中，

     
 onRestoreInstanceState方法在首次onCreate事并不会被执行，只有 运行时 内存不足 杀死activity后 从新回到 activity的时候 才会被执行 该方法

     *

     * <p>This method is called before an activity may be killed so that when it

     * comes back some time in the future it can restore its state.  For example,

     * if activity B is launched in front of activity A, and at some point activity

     * A is killed to reclaim resources, activity A will have a chance to save the

     * current state of its user interface via this method so that when the user

     * returns to activity A, the state of the user interface can be restored

     * via {@link #onCreate} or {@link #onRestoreInstanceState}.

    

     *

     * <p>Do not confuse this method with activity lifecycle callbacks such as

     * {@link #onPause}, which is always called when an activity is being placed

     * in the background or on its way to destruction, or {@link #onStop} which

     * is called before destruction.  One example of when {@link #onPause} and

     * {@link #onStop} is called and not this method is when a user navigates back

     * from activity B to activity A: there is no need to call {@link #onSaveInstanceState}

     * on B because that particular instance will never be restored, so the

     * system avoids calling it.  An example when {@link #onPause} is called and

     * not {@link #onSaveInstanceState} is when activity B is launched in front of activity A:

     * the system may avoid calling {@link #onSaveInstanceState} on activity A if it isn't

     * killed during the lifetime of B since the state of the user interface of

     * A will stay intact.

     大致意思是 不要认为这个方法一定会在onPause和onStop之间调用，如过是你自己主动终止结束这个activity将不会执行这个方法，因为你确定要关闭finish不需要保存任何状 态；

    

   总结来说，这个方法只会在activity将要进入 安卓堆栈第二层的时候 执行 ，目的是当系统资源不足，运行时 回收内存，杀死activty时保存状态，当activity被回退执行onCreate和onRestoreInstanceState时回复之前的状态；

    2，执行时间：

      安卓高级开发一书上说是在onpause之前执行，话说尽信书 不如无书，实际运行发现，是在onpause和onstop之前执行，而且在onpause执行完大概有1s的延迟时间，

可以安全的认为该方法在进程终止之前一定被调用。