How to Use Firebase to Build Real-Time Apps for Android

• To read data from the Firebase Realtime Database, you can add a ‘ValueEventListener’ to a database reference:

import com.google.firebase.database.DatabaseReference;

import com.google.firebase.database.FirebaseDatabase;

import com.google.firebase.database.DataSnapshot;

import com.google.firebase.database.DatabaseError;

import com.google.firebase.database.ValueEventListener;

// Get a reference to the root node of your database

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();

// Read data once

rootRef.child(“path/to/data”).addListenerForSingleValueEvent(new ValueEventListener() {

    @Override

    public void onDataChange(DataSnapshot dataSnapshot) {

        // Handle the retrieved data

        Object value = dataSnapshot.getValue();

        // …

    }

    @Override

    public void onCancelled(DatabaseError databaseError) {

        // Handle errors

        // …

    }

});

// Read data continuously

rootRef.child(“path/to/data”).addValueEventListener(new ValueEventListener() {

    @Override

    public void onDataChange(DataSnapshot dataSnapshot) {

        // Handle the retrieved data

        Object value = dataSnapshot.getValue();

        // …

    }

    @Override

    public void onCancelled(DatabaseError databaseError) {

        // Handle errors

        // …

    }

});

• To write data to the Firebase Realtime Database, you can use the ‘setValue()’ method on a database reference:

// Write a single value

rootRef.child(“path/to/data”).setValue(“Hello, Firebase!”);

// Write multiple values

Map<String, Object> data = new HashMap<>();

data.put(“key1”, value1);

data.put(“key2”, value2);

rootRef.child(“path/to/data”).updateChildren(data);