* <ul> * <li> {@link #onCreate} is where you initialize your activity. Most * importantly, here you will usually call {@link #setContentView(int)} * with a layout resource defining your UI, and using {@link #findViewById} * to retrieve the widgets in that UI that you need to interact with * programmatically.
onCreate是初始化你的Activity，在这里你可以调用setContentView(int)与layout资源来定义你的UI界面。使用findViewById来取出您交互的控件
* <li> {@link #onPause} is where you deal with the user leaving your * activity. Most importantly, any changes made by the user should at this * point be committed (usually to the * {@link android.content.ContentProvider} holding the data). * </ul>
这句的意思是说，onPause是处理用户离开时的方法。最重要的，任何用户操作产生的数据应该在这里进行提交，使用android.content.ContentProvider}来保存数据。
Because of this, you should use the onPause method to write any persistent data (such as user edits) to storage. In addition, the method onSaveInstanceState(Bundle) is called before placing the activity in such a background state, allowing you to save away any dynamic instance state in your activity into the given Bundle, to be later received in onCreate if the activity needs to be re-created. See the Process Lifecycle section for more information on how the lifecycle of a process is tied to the activities it is hosting. Note that it is important to save persistent data in onPause instead of onSaveInstanceState because the later is not part of the lifecycle callbacks, so will not be called in every situation as described in its documentation.
我们可以使用onSaveInstanceState(Bundle)方法进行存储，然后onRestoreInstanceState 处进行处理，即拿到值。
如何使用onSaveInstanceState(Bundle)方法？
// 将数据保存到savedInstanceState对象中, 该对象会在重建activity时传递给onCreate方法 @Override protected void onSaveInstanceState(Bundle savedInstanceState) { super.onSaveInstanceState(savedInstanceState); } @Override protected void onRestoreInstanceState(Bundle savedInstanceState) { super.onRestoreInstanceState(savedInstanceState); }
这种方式可以在旋转的时候进行数据保存，但是使用Actionbar向上跳不行，原因是：
* <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.
不要将这个方法和activity生命周期回调如onPause()或onStop()搞混淆了，onPause()在activtiy被放置到背景或者自行销毁时总会被调用，onStop()在activity被销毁时被调用。一个会调用onPause()和onStop()，但不触发onSaveInstanceState的例子是当用户从activity B返回到activity A时：没有必要调用B的onSaveInstanceState(Bundle)，此时的B实例永远不会被恢复，因此系统会避免调用它。一个调用onPause()但不调用onSaveInstanceState的例子是当activity B启动并处在activity A的前端：如果在B的整个生命周期里A的用户界面状态都没有被破坏的话，系统是不会调用activity A的onSaveInstanceState(Bundle)的。（http://blog.csdn.net/ddna/article/details/5123482）
(1)、当用户按下HOME键时。
这是显而易见的，系统不知道你按下HOME后要运行多少其他的程序，自然也不知道activity A是否会被销毁，因此系统会调用onSaveInstanceState()，让用户有机会保存某些非永久性的数据。以下几种情况的分析都遵循该原则
(2)、长按HOME键，选择运行其他的程序时。
(3)、按下电源按键（关闭屏幕显示）时。
(4)、从activity A中启动一个新的activity时。
(5)、屏幕方向切换时，例如从竖屏切换到横屏时。
在屏幕切换之前，系统会销毁activity A，在屏幕切换之后系统又会自动地创建activity A，所以onSaveInstanceState()一定会被执行，且也一定会执行onRestoreInstanceState()。
特别说明
如果我们没覆写onSaveInstanceState()方法,此方法会默认自动保存Activity中的某些数据，比如UI控件的状态和值，前提是需要指定控件一个唯一的ID，否则控件的数据不会出现保存。
那么什么时候保存覆写这个方法？
如果需要保存额外的数据时, 就需要覆写onSaveInstanceState()方法。大家需要注意的是：onSaveInstanceState()方法只适合保存瞬态数据, 比如UI控件的状态, 成员变量的值等，而不应该用来保存持久化数据，持久化数据应该当用户离开当前的 activity时，在 onPause() 中保存（比如将数据保存到数据库或文件中）。说到这里，还要说一点的就是在onPause()中不适合用来保存比较费时的数据，所以这点要理解。
至于onRestoreInstanceState方法，需要注意的是，onSaveInstanceState方法和onRestoreInstanceState方法“不一定”是成对的被调用的，onRestoreInstanceState被调用的前提是，activity A“确实”被系统销毁了，而如果仅仅是停留在有这种可能性的情况下，则该方法不会被调用，例如，当正在显示activity A的时候，用户按下HOME键回到主界面，然后用户紧接着又返回到activity A，这种情况下activity A一般不会因为内存的原因被系统销毁，故activity A的onRestoreInstanceState方法不会被执行
到此我们解决我们的问题：
