> For the complete documentation index, see [llms.txt](https://kaleb-is-caleb.gitbook.io/infosys/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://kaleb-is-caleb.gitbook.io/infosys/fragments/fragment-communication.md). # Fragment Communication **Activity can send data to Fragment and receive data from Fragment** All Fragment-to-Fragment communication is done through host Activity
### `RatingFragment`Setup Add a `String`variable and `float` value, we will be using this to place inside the `Bundle` ```java 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()`: ```java interface OnFragmentInteractionListener { void onRatingChoice(int choice); } ``` Add a variable for the listener later ```java OnFragmentInteractionListener mListener; ``` Override the [`onAttach()`](https://developer.android.com/reference/android/app/Fragment.html#onAttach\(android.app.Activity\)) lifecycle method in `SimpleFragment` to capture the host `Activity` interface implementation: ```java @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. {% hint style="info" %} The string resource `exception_message` is included in the **source code** for the text `"must implement OnFragmentInteractionListener"` {% endhint %} Overall, your class should end up looking like this. ```java 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 ```java 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 ```java private float mRatingChoice = 0; // The default (no choice). static final String STATE_CHOICE = "user_choice"; ``` ```java @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` ```java @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`](https://developer.android.com/reference/android/os/Bundle.html) and use the `Fragment.`[`setArguments(Bundle)`](https://developer.android.com/reference/android/app/Fragment.html#setArguments\(android.os.Bundle\)) 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` ```java 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 ```java 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);` ```java 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 `Fragment`which should display the choice you made previously always #### End Result: ```java 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.