Avoiding null pointer exceptions when passing events back from fragment to activity

MyActivity.java

package com.example;

import android.app.Activity;

public class MyActivity extends Activity
        implements MyFragment.Callbacks {

    @Override
    public void onItemClick(Object object) {
        //Do thing with the passed object

    }



}

MyFragment.java

package com.example;

import android.app.Activity;
import android.app.ListFragment;

public class MyFragment extends ListFragment {

    private Callbacks mCallbacks = sDummyCallbacks;



    private static Callbacks sDummyCallbacks = new Callbacks() {
        @Override
        public void onItemClick(Object object) {
            //Do nothing
        }
    };

    public interface Callbacks {
        public void onItemClick(Object object);
    }
    
    
    
    public void onWhateverEventWeAreDealingWith() {
        mCallbacks.onItemClick(someObject);
    }
    
    /*
     * We switch between the dummy callbackhandler and the host activity as callback handler
     * when the fragment attaches or detaches from the activity, thus we don't have to worry
     * when we call the callbacks whether activity is null or not. Callbacks will always be
     * valid
     * 
     */

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        if (! (activity instanceof Callbacks))
            throw new IllegalStateException("Host activity for MyFragment must implement MyFragment.Callbacks");

        mCallbacks = (Callbacks) activity;
    }

    @Override
    public void onDetach() {
        mCallbacks = sDummyCallbacks;
        super.onDetach();
    }



}