Activity 中的 onPause() 和 onStop()

I'm not sure which emulator you are testing with, but onPause is the one method that is always guaranteed to be called when your Activity loses focus (and I say always because on some devices, specifically those running Android 3.2+, onStop is not always guaranteed to be called before the Activity is destroyed).

对于初学者来说，了解 Activity 生命周期的一个好方法是用 Log 乱扔你的重写方法.例如:

A nice way to understand the Activity lifecycle for beginners is to litter your overriden methods with Logs. For example:

public class SampleActivity extends Activity {

    /**
     * A string constant to use in calls to the "log" methods. Its
     * value is often given by the name of the class, as this will 
     * allow you to easily determine where log methods are coming
     * from when you analyze your logcat output.
     */
    private static final String TAG = "SampleActivity";

    /**
     * Toggle this boolean constant's value to turn on/off logging
     * within the class. 
     */
    private static final boolean VERBOSE = true;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (VERBOSE) Log.v(TAG, "+++ ON CREATE +++");
    }

    @Override
    public void onStart() {
        super.onStart();
        if (VERBOSE) Log.v(TAG, "++ ON START ++");
    }

   @Override
    public void onResume() {
        super.onResume();
        if (VERBOSE) Log.v(TAG, "+ ON RESUME +");
    }

    @Override
    public void onPause() {
        super.onPause();
        if (VERBOSE) Log.v(TAG, "- ON PAUSE -");
    }

    @Override
    public void onStop() {
        super.onStop();
        if (VERBOSE) Log.v(TAG, "-- ON STOP --");
    }

   @Override
    public void onDestroy() {
        super.onDestroy();
        if (VERBOSE) Log.v(TAG, "- ON DESTROY -");
    }
}

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