B: 2 - Butterknife binding in onViewCreated vs onViewStateRestored

ButterknifeBindingExample.java

/**
 * Logs lifecycle events and provides subclasses a method to bind the views, bindViews().
 * 
 * Note that the bindViews() uses Butterknife to bind the views. However, the views
 * can also be bound without using Butterknife. Using Butterknife or not
 * plays no part in this demonstration.
 */
// BaseFragment.java
public abstract class BaseFragment extends Fragment {

    private static final String TAG = MainFragment.class.getSimpleName();

    private Unbinder unbinder;

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        Log.d(TAG, "onAttach");
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate - savedInstanceState is null? " + (savedInstanceState == null));
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        Log.d(TAG, "onCreateView - savedInstanceState is null? " + (savedInstanceState == null));
        return inflater.inflate(R.layout.fragment_main, container, false);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        Log.d(TAG, "onViewCreated - savedInstanceState is null? " + (savedInstanceState == null));
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Log.d(TAG, "onActivityCreated - savedInstanceState is null? " + (savedInstanceState == null));
    }

    @Override
    public void onViewStateRestored(Bundle savedInstanceState) {
        super.onViewStateRestored(savedInstanceState);
        Log.d(TAG, "onViewStateRestored - savedInstanceState is null? " + (savedInstanceState == null));
    }

    @Override
    public void onResume() {
        super.onResume();
        Log.d(TAG, "onResume");
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        unbinder.unbind();
    }

    @OnCheckedChanged(R.id.checkedTextView)
    void onCheckBoxCheckedChanged(boolean checked) {
        Log.d(TAG, "onCheckBoxCheckedChanged - " + checked);
        if (checked) {
            doSomethingWhenChecked();
        }
    }
  
    protected void bindViews() {
        unbinder = ButterKnife.bind(this, getView());
    }

    private void doSomethingWhenChecked() {
        Log.d(TAG, "Maybe do a background operation that updates some user data locally or over the network");
        // Maybe bind views with data.
        // Maybe do magic!
    }
}

/**
 * The following lifecycle events occur after checking the checkBox and rotating the device,
 * which triggers Fragment recreation.
 * 
 * D: onAttach
 * D: onCreate - savedInstanceState is null? false
 * D: onCreateView - savedInstanceState is null? false
 * D: onViewCreated - savedInstanceState is null? false
 * D: onActivityCreated - savedInstanceState is null? false
 * D: onCheckBoxCheckedChanged - true
 * D: Maybe do a background operation that updates some user data locally or over the network
 * D: onViewStateRestored - savedInstanceState is null? false
 * D: onResume
 * 
 * Notice that onCheckBoxCheckedChanged is triggered during the (re)creation of the Fragment
 * because Android itself saves and restores the states of views.
 * 
 * This may produce unwanted side-effects; such as performing a background
 * operation that updates some user data locally or over the network would be triggered 
 * without direct user action. In other words, a piece of code will get implicitly triggered
 * during recreation, which is something that we may not want.
 * 
 * You may use this side-effect to your advantage in your own project if so desired.
 * However, do be aware of this side-effect as it is not limited to CheckedChanged events.
 * This is also the case for SeekBarChange events, RatingBarChange events, and TextChanged events.
 */
// BindViewsInOnViewCreatedFragment.java
public final class BindViewsInOnViewCreatedFragment extends BaseFragment {
    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        bindViews();
    }
}

/**
 * The following lifecycle events occur after checking the checkBox and rotating the device,
 * which triggers Fragment recreation.
 * 
 * D: onAttach
 * D: onCreate - savedInstanceState is null? false
 * D: onCreateView - savedInstanceState is null? false
 * D: onViewCreated - savedInstanceState is null? false
 * D: onActivityCreated - savedInstanceState is null? false
 * D: onViewStateRestored - savedInstanceState is null? false
 * D: onResume
 * 
 * Notice that onCheckBoxCheckedChanged is NOT triggered during the (re)creation of the Fragment
 * because the OS has finished restoring the state of views at this point.
 * 
 * This means that CheckedChanged events (among other similar events), will not trigger unless
 * explicitly triggered (usually by the user). This is the desired behavior in all of the projects
 * I have worked on so far.
 */
// BindViewsInOnViewStateRestoredFragment.java
public final class BindViewsInOnViewStateRestoredFragment extends BaseFragment {
    @Override
    public void onViewStateRestored(Bundle savedInstanceState) {
        super.onViewStateRestored(savedInstanceState);
        bindViews();
    }
}