Android Fragment Activity Communication

ChangeColorFragment.java

public class ChangeColorFragment extends Fragment {

    private OnChangeColorFragmentInteractionListener mListener;
    RadioGroup radioGroupColors;

    public ChangeColorFragment() {
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view= inflater.inflate(R.layout.fragment_change_color, container, false);

        radioGroupColors= (RadioGroup) view.findViewById(R.id.radioGroupColors);

        radioGroupColors.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup group, int checkedId) {
                onColorChanged(checkedId);
            }
        });

        return view;
    }

    public void onColorChanged(int id) {
        if (mListener != null) {
            mListener.onChangeColorFragmentInteraction(id);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnChangeColorFragmentInteractionListener) {
            mListener = (OnChangeColorFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnChangeColorFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface OnChangeColorFragmentInteractionListener {
        void onChangeColorFragmentInteraction(int id);
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity implements ChangeColorFragment.OnChangeColorFragmentInteractionListener{

    RelativeLayout layout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        layout= (RelativeLayout) findViewById(R.id.activity_main);

        FragmentTransaction transaction= getSupportFragmentManager().beginTransaction();

        ChangeColorFragment changeColorFragment=new ChangeColorFragment();
        transaction.add(R.id.relativeLayoutFragmentContainer,changeColorFragment);

        transaction.commit();
    }

    @Override
    public void onChangeColorFragmentInteraction(int id) {
        switch (id)
        {
            case R.id.radioButtonRed:
                layout.setBackgroundColor(getResources().getColor(R.color.red));
                break;
            case R.id.radioButtonBlue:
                layout.setBackgroundColor(getResources().getColor(R.color.blue));
                break;
        }
    }
}

References
https://github.com/mhdr/AndroidSamples/tree/master/031