# 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.
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