Fragment Communication

Activity can send data to Fragment and receive data from Fragment

All Fragment-to-Fragment communication is done through host Activity

RatingFragmentSetup

Add a Stringvariable and float value, we will be using this to place inside the Bundle

private static final String CHOICE="choice";
public float choice;

Define a listener interface called OnFragmentInteractionListener. In it, specify a callback method that you will create, called onRadioButtonChoice():

interface OnFragmentInteractionListener {
    void onRatingChoice(int choice);
}

Add a variable for the listener later

OnFragmentInteractionListener mListener;

Override the onAttach() lifecycle method in SimpleFragment to capture the host Activity interface implementation:

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    if (context instanceof OnFragmentInteractionListener) {
        mListener = (OnFragmentInteractionListener) context;
    } else {
        throw new ClassCastException(context.toString()
           + getResources().getString(R.string.exception_message));
    }
}

The onAttach() method is called as soon as the Fragment is associated with the Activity. The code makes sure that the host Activity has implemented the callback interface. If not, it throws an exception.

The string resource exception_message is included in the source code for the text "must implement OnFragmentInteractionListener"

Overall, your class should end up looking like this.

public class RatingFragment extends Fragment {
    private static final String CHOICE="choice";
    public float choice;
    OnFragmentInteractionListener mListener;

    interface OnFragmentInteractionListener {
        void onRatingChoice(float choice);
    }

    public RatingFragment() {
        // Required empty public constructor

    }

    public static RatingFragment newInstance(float choice) {
        RatingFragment fragment = new RatingFragment();
        Bundle arguments = new Bundle();
        arguments.putFloat(CHOICE, choice);
        fragment.setArguments(arguments);
        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        final View rootView = inflater.inflate(R.layout.fragment_rating, container, false);
        final RatingBar rB = rootView.findViewById(R.id.ratingBar);
        if (getArguments().containsKey(CHOICE)) {
            // A choice was made, so get the choice.
            choice = getArguments().getFloat(CHOICE);
            // Check the radio button choice.
            if (choice!=0) {
                rB.setRating(choice);
            }
        }

        rB.setOnRatingBarChangeListener(new RatingBar.OnRatingBarChangeListener() {
            @Override
            public void onRatingChanged(RatingBar ratingBar, float v, boolean b) {
                String s = getString(R.string.rating_message);
                choice = v;
                mListener.onRatingChoice(v);
                //Toast.makeText(getActivity().getApplicationContext(),s+ " "+ v,Toast.LENGTH_SHORT).show();
            }
        });
        return rootView;
    }
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new ClassCastException(context.toString()
                    + getResources().getString(R.string.exception_message));
        }
    }

}

Implementing OnFragmentInteractionListener

Now that we have set up our RatingListener for communication. We need to implement the OnFragmentInteractionListener in the activity in order to receive data from fragment

public class MainActivity extends AppCompatActivity
        implements RatingFragment.OnFragmentInteractionListener {

Add a member variable in MainActivity for the choice the user makes with the RatingBar, and set it to the default value

private float mRatingChoice = 0; // The default (no choice).
static final String STATE_CHOICE = "user_choice";

@Override
    public void onRatingChoice(float choice) {
        mRatingChoice = choice;
        Toast.makeText(this,"Choice is "+ Float.toString(choice),Toast.LENGTH_SHORT).show();
}

Set up the onSaveInstanceState(Bundle) to save our float variable and states for the Activity

@Override
public void onSaveInstanceState(Bundle savedInstanceState){
        savedInstanceState.putBoolean(STATE_FRAGMENT,isFragmentDisplayed);
        savedInstanceState.putFloat(STATE_CHOICE, mRatingChoice);
        super.onSaveInstanceState(savedInstanceState);
    }

The app should now show a toast when you click it.

Providing user's choice to fragment (Main

We have to now set a Bundle and use the Fragment.setArguments(Bundle) method to supply the construction arguments for the Fragment.

A Bundle is like a key-value dictionary which allows to transfer information to other activities, fragments.

First, let's setup a newInstance() method to use a Bundle and setArguments

 public static RatingFragment newInstance(float choice) {
        RatingFragment fragment = new RatingFragment();
        Bundle arguments = new Bundle();
        arguments.putFloat(CHOICE, choice);
        fragment.setArguments(arguments);
        return fragment;
    }

Add following code to onCreateView() method to retrieve the previously set value of choice

if (getArguments().containsKey(CHOICE)) {
            // A choice was made, so get the choice.
            choice = getArguments().getFloat(CHOICE);
            // Check the radio button choice.
            if (choice!=0) {
                rB.setRating(choice);
            }
        }

Lastly, we need to change our functions in MainActivity to RatingFragment.newInstance(mRatingChoice);

public void displayFragment(){
        RatingFragment ratingFragment = RatingFragment.newInstance(mRatingChoice);
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.add(R.id.fragment_container,ratingFragment).addToBackStack(null).commit();
        sButtonl.setText(R.string.button_carClose);
        isFragmentDisplayed = true;
    }
    public void closeFragment(){
        FragmentManager fragmentManager = getSupportFragmentManager();
        RatingFragment ratingFragment = (RatingFragment)fragmentManager.findFragmentById(R.id.fragment_container);
        if(ratingFragment!=null){
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.remove(ratingFragment).addToBackStack(null).commit();
        }
        sButtonl.setText(R.string.button_car);
        isFragmentDisplayed = false;

    }

Your app should be communicating the choice from the Fragment to the Activity, and then back to the Fragmentwhich should display the choice you made previously always

End Result:

public class MainActivity extends AppCompatActivity implements RatingFragment.OnFragmentInteractionListener{
    Button sButtonl;
    private Boolean isFragmentDisplayed = false;
    static final String STATE_FRAGMENT = "state_of_fragment";
    private float mRatingChoice = 0;
    static final String STATE_CHOICE = "user_choice";

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

        sButtonl = findViewById(R.id.button);
        sButtonl.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(!isFragmentDisplayed){
                    displayFragment();
                }else{
                    closeFragment();
                }
            }
        });
        if(savedInstanceState!=null){
            isFragmentDisplayed = savedInstanceState.getBoolean(STATE_FRAGMENT);
            mRatingChoice = savedInstanceState.getInt(STATE_CHOICE);
        }

    }
    @Override
    public void onSaveInstanceState(Bundle savedInstanceState){
        savedInstanceState.putBoolean(STATE_FRAGMENT,isFragmentDisplayed);
        savedInstanceState.putFloat(STATE_CHOICE, mRatingChoice);
        super.onSaveInstanceState(savedInstanceState);
    }
    public void displayFragment(){
        RatingFragment ratingFragment = RatingFragment.newInstance(mRatingChoice);
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.add(R.id.fragment_container,ratingFragment).addToBackStack(null).commit();
        sButtonl.setText(R.string.button_carClose);
        isFragmentDisplayed = true;
    }
    public void closeFragment(){
        FragmentManager fragmentManager = getSupportFragmentManager();
        RatingFragment ratingFragment = (RatingFragment)fragmentManager.findFragmentById(R.id.fragment_container);
        if(ratingFragment!=null){
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.remove(ratingFragment).addToBackStack(null).commit();
        }
        sButtonl.setText(R.string.button_car);
        isFragmentDisplayed = false;

    }


    @Override
    public void onRatingChoice(float choice) {
        mRatingChoice = choice;
        Toast.makeText(this,"Choice is "+ Float.toString(choice),Toast.LENGTH_SHORT).show();
    }
}

From this point, there are more complicated paths and communications you can perform, but these steps lay a foundation in using them.