Question

I am making my first Android app, which consists of just editText’s and Spinner’s. Reading up on the activity cycle, I am wondering if it is even necessary to use the Bundle mechanism in my situation.

Since the state of the widgets are automatically persisted –
could I just call the getSelectedItem() method on the spinners and getText() on the EditText’s within the onCreate() method for the Activity and pass that on to my newly re-created model object rather than using the Bundle mechanism? What are the advantages and disadvatanges of this approach?

Answer 1

The state of widgets it not automatically persisted. When you activity is destroyed it loses all the information about state. I recommend you saving you application state using shared preferences. Here is an example from google developers site. it allows you to save your application state by storing key-value pairs and it should suffice for your app.

Save the text and spinner item position in shared preferences when your activity is stopped – onStop() and restore the state in onCreate().

public class Calc extends Activity {
    public static final String PREFS_NAME = "MyPrefsFile";

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

       // Restore preferences
       SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
       boolean silent = settings.getBoolean("silentMode", false);
       setSilent(silent);
    }

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

      // We need an Editor object to make preference changes.
      // All objects are from android.context.Context
      SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
      SharedPreferences.Editor editor = settings.edit();
      editor.putBoolean("silentMode", mSilentMode);

      // Commit the edits!
      editor.commit();
    }
}

Although you can save your application state by onSaveInstanceState(Bundle) method, usually the better way will be to do that in onPause() or onStop() methods(the data will be saved for sure). Documentation says:

Note that it is important to save persistent data in onPause() instead
of onSaveInstanceState(Bundle) because the latter is not part of the
lifecycle callbacks, so will not be called in every situation as
described in its documentation.