两种保存状态的方法getSharedPreferences和onSaveInstanceState

虽然这些东西很简单有时候还真的让你搞混

@Override
protected void onPause() {
super.onPause();

SharedPreferences prefs = getSharedPreferences("X", MODE_PRIVATE);
Editor editor = prefs.edit();
editor.putString("lastActivity", getClass().getName());
editor.commit();
}

public class Dispatcher extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

Class<?> activityClass;

try {
SharedPreferences prefs = getSharedPreferences("X", MODE_PRIVATE);
activityClass = Class.forName(
prefs.getString("lastActivity", Activity1.class.getName()));
} catch(ClassNotFoundException ex) {
activityClass = Activity1.class;
}

startActivity(new Intent(this, activityClass));
}
}

上面的方法通常保存一个activity以便下次发动

2.

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putBoolean("MyBoolean", true);
savedInstanceState.putDouble("myDouble", 1.9);
savedInstanceState.putInt("MyInt", 1);
savedInstanceState.putString("MyString", "Welcome back to Android");
// etc.
super.onSaveInstanceState(savedInstanceState);
}
@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}

这个上次已经记过了用来旋转保存状态最好

对onSaveInstanceState的解释：

        为了获取activity被杀死前的状态，你应该为activity实现onSaveInstanceState() 方法。Android在activity有可能被销毁之前（即onPause() 调用之前）会调用此方法。它会将一个以名称-值对方式记录了activity动态状态的Bundle 对象传递给该方法。当activity再次启动时，这个Bundle会传递给onCreate()方法和随着onStart()方法调用的onRestoreInstanceState()，所以它们两个都可以恢复捕获的状态。

         与onPause()或先前讨论的其它方法不同，onSaveInstanceState() 和 onRestoreInstanceState() 并不是生命周期方法。它们并不是总会被调用。比如说，Android会在activity易于被系统销毁之前调用 onSaveInstanceState()，但用户动作（比如按下了BACK键）造成的销毁则不调用。在这种情况下，用户没打算再次回到这个activity，所以没有保存状态的必要。

         因为onSaveInstanceState()不是总被调用，所以你应该只用它来为activity保存一些临时的状态，而不能用来保存持久性数据。而是应该用onPause()来达到这个目的。

Google为何这样设计OnSharedPreferenceChangeListener

http://droidyue.com/blog/2014/11/29/why-onsharedpreferencechangelistener-was-not-called/