Add listeners for Push notifications using Firebase

App.js

import firebase from 'react-native-firebase';

export default class App extends Component {

async componentDidMount() {
  this.checkPermission();
  this.createNotificationListeners(); //add this line
}

////////////////////// Add these methods //////////////////////
  
  //Remove listeners allocated in createNotificationListeners()
componentWillUnmount() {
  this.notificationListener();
  this.notificationOpenedListener();
}

async createNotificationListeners() {
  /*
  * Triggered when a particular notification has been received in foreground
  * */
  this.notificationListener = firebase.notifications().onNotification((notification) => {
      const { title, body } = notification;
      this.showAlert(title, body);
  });

  /*
  * If your app is in background, you can listen for when a notification is clicked / tapped / opened as follows:
  * */
  this.notificationOpenedListener = firebase.notifications().onNotificationOpened((notificationOpen) => {
      const { title, body } = notificationOpen.notification;
      this.showAlert(title, body);
  });

  /*
  * If your app is closed, you can check if it was opened by a notification being clicked / tapped / opened as follows:
  * */
  const notificationOpen = await firebase.notifications().getInitialNotification();
  if (notificationOpen) {
      const { title, body } = notificationOpen.notification;
      this.showAlert(title, body);
  }
  /*
  * Triggered for data only payload in foreground
  * */
  this.messageListener = firebase.messaging().onMessage((message) => {
    //process data message
    console.log(JSON.stringify(message));
  });
}

showAlert(title, body) {
  Alert.alert(
    title, body,
    [
        { text: 'OK', onPress: () => console.log('OK Pressed') },
    ],
    { cancelable: false },
  );
}
}