android-Recreating an Activity

when the user presses the Back button or your activity signals its own destruction by calling finish(). The system may also destroy your activity if it's currently stopped and hasn't been used in a long time or the foreground activity requires more resources so the system must shut down background processes to recover memory.

When your activity is destroyed because the user presses Backor the activity finishes itself, the system's concept of thatActivity instance is gone forever because the behavior indicates the activity is no longer needed.

By default, the system uses the Bundle instance state to save information about each View object in your activity layout (such as the text value entered into an EditText object). So, if your activity instance is destroyed and recreated, the state of the layout is restored to its previous state with no code required by you.

Note: In order for the Android system to restore the state of the views in your activity, each view must have a unique ID, supplied by the android:id attribute.

> To save additional data about the activity state, you must override the onSaveInstanceState() callback method. The system calls this method when the user is leaving your activity and passes it the Bundle object that will be saved in the event that your activity is destroyed unexpectedly. If the system must recreate the activity instance later, it passes the same Bundle object to both the onRestoreInstanceState() andonCreate() methods.

static final String STATE_SCORE = "playerScore";static final String STATE_LEVEL = "playerLevel";...@Overridepublic void onSaveInstanceState(Bundle savedInstanceState) {    // Save the user's current game state    savedInstanceState.putInt(STATE_SCORE, mCurrentScore);    savedInstanceState.putInt(STATE_LEVEL, mCurrentLevel);        // Always call the superclass so it can save the view hierarchy state    super.onSaveInstanceState(savedInstanceState);}

@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState); // Always call the superclass first       // Check whether we're recreating a previously destroyed instance    if (savedInstanceState != null) {        // Restore value of members from saved state        mCurrentScore = savedInstanceState.getInt(STATE_SCORE);        mCurrentLevel = savedInstanceState.getInt(STATE_LEVEL);    } else {        // Probably initialize members with default values for a new instance    }    ...}

public void onRestoreInstanceState(Bundle savedInstanceState) {    // Always call the superclass so it can restore the view hierarchy    super.onRestoreInstanceState(savedInstanceState);       // Restore state members from saved instance    mCurrentScore = savedInstanceState.getInt(STATE_SCORE);    mCurrentLevel = savedInstanceState.getInt(STATE_LEVEL);}

Caution: Always call the superclass implementation of onRestoreInstanceState() so the default implementation can restore the state of the view hierarchy.