Connect your App to Firebase

If you haven't already, add Firebase to your Android project.

Create a Database

1. Navigate to the Realtime Database section of the Firebase console. You'll be prompted to select an existing Firebase project. Follow the database creation workflow.

2. Select a starting mode for your Firebase Security Rules:

   Test mode

   Good for getting started with the mobile and web client libraries, but allows anyone to read and overwrite your data. After testing, make sure to review the Understand Firebase Realtime Database Rules section.

   To get started with the web, Apple, or Android SDK, select testmode.

   Locked mode

   Denies all reads and writes from mobile and web clients. Your authenticated application servers can still access your database.

3. Choose a location for the database.

   Depending on the location of the database, the URL for the new database will be in one of the following forms:

   • DATABASE_NAME.firebaseio.com (for databases in us-central1)

   • DATABASE_NAME.REGION.firebasedatabase.app (for databases in all other locations)

4. Click Done.

When you enable Realtime Database, it also enables the API in the Cloud API Manager.

Add the Realtime Database SDK to your app

dependencies {
    // Import the BoM for the Firebase platform
    implementation(platform("com.google.firebase:firebase-bom:33.6.0"))

    // Add the dependency for the Realtime Database library
    // When using the BoM, you don't specify versions in Firebase library dependencies
    implementation("com.google.firebase:firebase-database")
}

By using the Firebase Android BoM, your app will always use compatible versions of Firebase Android libraries.

dependencies {
    // Add the dependency for the Realtime Database library
    // When NOT using the BoM, you must specify versions in Firebase library dependencies
    implementation("com.google.firebase:firebase-database:21.0.0")
}

Configure Realtime Database Security Rules

The Realtime Database provides a declarative rules language that allows you to define how your data should be structured, how it should be indexed, and when your data can be read from and written to.

Write to your database

Retrieve an instance of your database using getInstance() and reference the location you want to write to.

// Write a message to the database
val database = Firebase.database
val myRef = database.getReference("message")

myRef.setValue("Hello, World!")
MainActivity.kt

// Write a message to the database
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("message");

myRef.setValue("Hello, World!");
MainActivity.java

You can save a range of data types to the database this way, including Java objects. When you save an object the responses from any getters will be saved as children of this location.

Read from your database

To make your app data update in realtime, you should add a ValueEventListener to the reference you just created.

The onDataChange() method in this class is triggered once when the listener is attached and again every time the data changes, including the children.

// Read from the database
myRef.addValueEventListener(object : ValueEventListener {
    override fun onDataChange(dataSnapshot: DataSnapshot) {
        // This method is called once with the initial value and again
        // whenever data at this location is updated.
        val value = dataSnapshot.getValue<String>()
        Log.d(TAG, "Value is: $value")
    }

    override fun onCancelled(error: DatabaseError) {
        // Failed to read value
        Log.w(TAG, "Failed to read value.", error.toException())
    }
})
MainActivity.kt

// Read from the database
myRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        // This method is called once with the initial value and again
        // whenever data at this location is updated.
        String value = dataSnapshot.getValue(String.class);
        Log.d(TAG, "Value is: " + value);
    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        // Failed to read value
        Log.w(TAG, "Failed to read value.", error.toException());
    }
});
MainActivity.java

Optional: Configure ProGuard

When using Firebase Realtime Database in your app along with ProGuard, you need to consider how your model objects will be serialized and deserialized after obfuscation. If you use DataSnapshot.getValue(Class) or DatabaseReference.setValue(Object) to read and write data, you will need to add rules to the proguard-rules.pro file:

    # Add this global rule
    -keepattributes Signature

    # This rule will properly ProGuard all the model classes in
    # the package com.yourcompany.models.
    # Modify this rule to fit the structure of your app.
    -keepclassmembers class com.yourcompany.models.** {
      *;
    }

To get help for questions or issues related to ProGuard, visit the Guardsquare Community forums to get assistance from an expert.

Prepare for Launch

Before launching your app, we recommend walking through our launch checklist to make sure your app is ready to go!

Be sure to enable App Check to help ensure that only your apps can access your databases.

Next Steps

• Learn how to structure data for Realtime Database
• Scale your data across multiple database instances.
• Read and write data.
• View your database in the Firebase console.