Using Firebase Database (Android)

The Firebase database is a NoSQL, real-time, and cloud-hosted database. Data is stored as JSON and synchronized in real-time to every connected client. The following steps show how to use the Firebase database:

†For the Web, check Using Firebase Database (Web).
  1. Open Android Studio and create a new project or open an existing project.

    2. ⇒

    ⇒

  2. In Android Studio, log in with your email address. You can find the login button at the top right corner of the Android Studio. (Remember the email address that you use here.)




    3. ⇒

    ⇒

    ⇒

    ⇒

  3. Go to Google Firebase console and make an account to gain access to their console.


  4. Start creating your first Firebase project:


    5. ⇒

    ⇒

    ⇒

    ⇒

    ⇒

    ⇒

    ⇒

    ⇒

    ⇒
    Select the “Test Mode.” Otherwise, your code has to include authentication. 

    ⇒

  5. Now, come back to your Android Studio project. Connect the Android Studio project to the Firebase project by clicking on Tools ⇒ Firebase ⇒ Realtime Database ⇒ Save and retrieve data.


  6. After that click on “Connect to Firebase,” a list of projects will be shown to you. Select the project that you have created on the Firebase website and click on “Connect to Firebase.”

    7. ⇒

    ⇒

  7. Next, you have to add the dependency of Firebase Database in your project by clicking on “Add the Realtime Database to your app” button and then “Accept Changes.”



    8. ⇓ (after checking “Add the Realtime Database to your app”)


    The build.gradle (Module: My_Firebase.app) file before adding the dependencies is

    MyFirebase\build.gradle (Module: My_Firebase.app) 
     plugins {
   id 'com.android.application'
 }
 android {
   compileSdkVersion 30
   buildToolsVersion "30.0.2"
   defaultConfig {
     applicationId "com.wenchen.myfirebase"
     minSdkVersion 16
     targetSdkVersion 30
     versionCode 1
     versionName "1.0"
     testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
   }
   buildTypes {
     release {
     minifyEnabled false
     proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'),
       'proguard-rules.pro'
     }
   }
   compileOptions {
     sourceCompatibility JavaVersion.VERSION_1_8
     targetCompatibility JavaVersion.VERSION_1_8
   }
 }
 dependencies {
   implementation 'androidx.appcompat:appcompat:1.2.0'
   implementation 'com.google.android.material:material:1.3.0'
   implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
   testImplementation 'junit:junit:4.+'
   androidTestImplementation 'androidx.test.ext:junit:1.1.2'
   androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
 }

    ⇓ (after adding the dependencies)

    MyFirebase\build.gradle (Module: My_Firebase.app) 
     plugins {
   id 'com.android.application'
   id 'com.google.gms.google-services'
 }

 android {
   compileSdkVersion 30
   buildToolsVersion "30.0.2"
   defaultConfig {
     applicationId "com.wenchen.myfirebase"
     minSdkVersion 16
     targetSdkVersion 30
     versionCode 1
     versionName "1.0"
     testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
   }
   buildTypes {
     release {
       minifyEnabled false
       proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 
         'proguard-rules.pro'
     }
   }
   compileOptions {
     sourceCompatibility JavaVersion.VERSION_1_8
     targetCompatibility JavaVersion.VERSION_1_8
   }
 }
 dependencies {
   implementation 'androidx.appcompat:appcompat:1.2.0'
   implementation 'com.google.android.material:material:1.3.0'
   implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
   implementation 'com.google.firebase:firebase-database:19.6.0'
   testImplementation 'junit:junit:4.+'
   androidTestImplementation 'androidx.test.ext:junit:1.1.2'
   androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
 }
    If there is an error of 

      File google-services.json is missing from module root folder. The Google Services Plugin cannot function without it.” 

    Take the following actions: 

    1. Go to Firebase Console . 
    2. Select your project. 
    3. Go to “settings ⇒ project settings.” 
    4. Download and add the google-services.json file to the app folder of your app at 

      MyFirebase\app\google-services.json 
  8. The rest of the code is given as follows:
    9. The AndroidManifest.xml file does not need to be changed as follows:

    MyFirebase\app\manifests\AndroidManifest.xml 
     <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
       package="com.wenchen.myfirebase">
   <application
       android:allowBackup = "true"
       android:icon        = "@mipmap/ic_launcher"
       android:label       = "@string/app_name"
       android:roundIcon   = "@mipmap/ic_launcher_round"
       android:supportsRtl = "true"
       android:theme       = "@style/Theme.MyFirebase">
     <activity android:name=".MainActivity">
       <intent-filter>
         <action android:name   = "android.intent.action.MAIN" />
         <category android:name = "android.intent.category.LAUNCHER" />
       </intent-filter>
     </activity>
   </application>
 </manifest>

    Add code to the main_activity.xml file. This application updates and shows the user’s profile consisting of a name and an email address. So, we will have one TextView for showing the profile and two EditTexts for getting the new values from the user, and an update button. The code for the main_activity.xml file is given as follows:

    MyFirebase\app\res\layout\activity_main.xml 
     <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools           = "http://schemas.android.com/tools"
     android:id            = "@+id/activity_main"
     android:layout_width  = "match_parent"
     android:layout_height = "match_parent"
     android:orientation   = "vertical"
     android:paddingBottom = "@dimen/activity_vertical_margin"
     android:paddingLeft   = "@dimen/activity_horizontal_margin"
     android:paddingRight  = "@dimen/activity_horizontal_margin"
     android:paddingTop    = "@dimen/activity_vertical_margin"
     tools:context         = "com.wenchen.myfirebase.MainActivity">
   <TextView
       android:id            = "@+id/txt_user"
       android:layout_width  = "wrap_content"
       android:layout_height = "wrap_content"
       android:paddingBottom = "@dimen/activity_horizontal_margin"
       android:paddingTop    = "@dimen/activity_horizontal_margin"
      android:textSize      = "20dp" />
   <LinearLayout
       android:layout_width  = "match_parent"
       android:layout_height = "wrap_content"
       android:orientation   = "vertical">
     <com.google.android.material.textfield.TextInputLayout
         android:layout_width  = "match_parent"
         android:layout_height = "wrap_content">
       <EditText
           android:id            = "@+id/name"
           android:layout_width  = "match_parent"
           android:layout_height = "wrap_content"
           android:hint          = "@string/name"
           android:inputType     = "textCapWords"
           android:maxLines      = "1" />
     </com.google.android.material.textfield.TextInputLayout>
     <com.google.android.material.textfield.TextInputLayout
         android:layout_width  = "match_parent"
         android:layout_height = "wrap_content">
       <EditText
         android:id            = "@+id/email"
         android:layout_width  = "match_parent"
         android:layout_height = "wrap_content"
         android:hint          = "@string/email"
         android:inputType     = "textEmailAddress"
         android:maxLines      = "1" />
     </com.google.android.material.textfield.TextInputLayout>
     <Button
         android:id               = "@+id/btn_save"
         style                    = "?android:textAppearanceSmall"
         android:layout_width     = "match_parent"
         android:layout_height    = "wrap_content"
         android:layout_marginTop = "16dp"
         android:background       = "@color/colorPrimary"
         android:text             = "@string/action_save"
         android:textColor        = "@android:color/white"
         android:textStyle        = "bold" />
   </LinearLayout>
 </LinearLayout>
    If there is an inflate error because of com.google.android.material.textfield.TextInputLayout, add the following line to the gradle file:  

     implementation 'com.google.android.material:material:1.0.0'
    The strings.xml file is given as follows:

    MyFirebase\app\res\values\strings.xml 
     <resources>
   <string name="app_name">My Firebase</string>
   <string name="hint_name">Full Name</string>
   <string name="hint_email">Email</string>
   <string name="action_save">Save</string>
   <string name="name">Name</string>
   <string name="email">Email</string>
 </resources>

    The dimens.xml file is given as follows:

    MyFirebase\app\res\values\dimens.xml 
     <resources>
   <!-- Default screen margins, per the Android Design guidelines. -->
   <dimen name="activity_horizontal_margin">16dp</dimen>
   <dimen name="activity_vertical_margin">16dp</dimen>
 </resources>

    The styles.xml file is given as follows:

    MyFirebase\app\res\values\styles.xml 
     <resources>
   <!-- Base application theme. -->
   <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
     <!-- Customize your theme here. -->
     <item name="colorPrimary">@color/colorPrimary</item>
     <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
     <item name="colorAccent">@color/colorAccent</item>
   </style>
 </resources>

    The colors.xml file is given as follows:

    MyFirebase\app\res\values\colors.xml 
     <resources>
   <color name="colorPrimary">#00bcd4</color>
   <color name="colorPrimaryDark">#0097a7</color>
   <color name="colorAccent">#0097a7</color>
 </resources>

    The MainActivity.java program saves the name and email address of a user in the Firebase database when starts a new session (emulator). Afterwards, only the current user’s profile (name and email address) can be updated unless another session starts, and the previous profiles are not able to be updated.

    MyFirebase\app\java\com\wenchen\myfriebase\MainActivity.java 
     package com.wenchen.myfirebase

 import android.os.Bundle;
 import androidx.appcompat.app.AppCompatActivity;
 import android.text.TextUtils;
 import android.util.Log;
 import android.view.View;
 import android.widget.Button;
 import android.widget.EditText;
 import android.widget.TextView;

 import com.google.firebase.database.DataSnapshot;
 import com.google.firebase.database.DatabaseError;
 import com.google.firebase.database.DatabaseReference;
 import com.google.firebase.database.FirebaseDatabase;
 import com.google.firebase.database.ValueEventListener;

 public class MainActivity extends AppCompatActivity {
   private static final String TAG = MainActivity.class.getSimpleName( );
   private TextView txtDetails;
   private EditText inputName, inputEmail;
   private Button btnSave;
   private DatabaseReference mFirebaseDatabase;
   private FirebaseDatabase mFirebaseInstance;
   private String userId;

   @Override
   protected void onCreate( Bundle savedInstanceState ) {
     super.onCreate( savedInstanceState );
     setContentView( R.layout.activity_main );
     // Displaying toolbar icon
     getSupportActionBar( ).setDisplayShowHomeEnabled( true );
     getSupportActionBar( ).setIcon( R.mipmap.ic_launcher );

     txtDetails = (TextView) findViewById( R.id.txt_user );
     inputName  = (EditText) findViewById( R.id.name );
     inputEmail = (EditText) findViewById( R.id.email );
     btnSave    = (Button)   findViewById( R.id.btn_save );

     mFirebaseInstance = FirebaseDatabase.getInstance( );
     // Getting reference to 'users' node
     mFirebaseDatabase = mFirebaseInstance.getReference( "users" );
     // Storing app title to 'app_title' node
     mFirebaseInstance.getReference( "app_title" ).setValue( "Realtime Database" );

     // app_title change listener
     mFirebaseInstance.getReference( "app_title" ).addValueEventListener(
       new ValueEventListener( ) {
         @Override
         public void onDataChange( DataSnapshot dataSnapshot ) {
           Log.e( TAG, "App title updated" );
           String appTitle = dataSnapshot.getValue( String.class );
           // Updating toolbar title
           getSupportActionBar( ).setTitle( appTitle );
         }
         @Override
         public void onCancelled( DatabaseError error ) {
           // Failed to read value
           Log.e( TAG, "Failed to read app title value.", error.toException( ) );
         }
       }
     );
     // Saving or updating the user
     btnSave.setOnClickListener( 
       new View.OnClickListener( ) {
         @Override
         public void onClick( View view ) {
           String name  = inputName.getText(  ).toString( );
           String email = inputEmail.getText( ).toString( );
           // Checking for already existed userId
           if ( TextUtils.isEmpty( userId ) )  createUser( name, email );
           else  updateUser( name, email );
         }
       }
     );
     toggleButton( );
   }
   // Changing button text
   private void toggleButton( ) {
     if ( TextUtils.isEmpty( userId ) )  btnSave.setText( "Save" );
     else  btnSave.setText( "Update" );
   }
   //
   //   Creating new user node under 'users'
   //
   private void createUser( String name, String email ) {
     // TODO
     // In real apps this userId should be fetched by using auth
     if ( TextUtils.isEmpty( userId ) )
       userId  = mFirebaseDatabase.push( ).getKey( );
     User user = new User( name, email );
     mFirebaseDatabase.child( userId ).setValue( user );
     addUserChangeListener( );
   }
   //
   //   User data change listener
   //
   private void addUserChangeListener( ) {
     mFirebaseDatabase.child( userId ).addValueEventListener( 
       new ValueEventListener( ) {
         @Override
         public void onDataChange( DataSnapshot dataSnapshot ) {
           User user = dataSnapshot.getValue( User.class );
           // Check for null
           if ( user == null ) {
             Log.e( TAG, "User data is null!" );
             return;
           }
           Log.e( TAG, "User data is changed!" + user.name + ", " + user.email );
           // Displaying newly updated name and email
           txtDetails.setText( user.name + ", " + user.email );
           // Clearing edit text
           inputEmail.setText( "" );
           inputName.setText ( "" );
           toggleButton( );
         }
         @Override
         public void onCancelled( DatabaseError error ) {
           // Failed to read value
           Log.e( TAG, "Failed to read user", error.toException( ) );
         }
       }
     );
   }
   private void updateUser( String name, String email ) {
     // Updating the user via child nodes
     if ( !TextUtils.isEmpty( name ) )
       mFirebaseDatabase.child( userId ).child( "name"  ).setValue( name );
     if ( !TextUtils.isEmpty( email ) )
       mFirebaseDatabase.child( userId ).child( "email" ).setValue( email );
   }
 }

    In order to save a user profile, we use a model class called User.java file to store the properties of name and email address (you can add few more properties like address, phone number, etc.):

    MyFirebase\app\java\com\wenchen\myfriebase\User.java 
     package com.wenchen.myfirebase
 import com.google.firebase.database.IgnoreExtraProperties;

 @IgnoreExtraProperties
 public class User {
   public String name;
   public String email;

   // Default constructor required for calls to
   // DataSnapshot.getValue( User.class )
   public User( ) { }

   public User( String name, String email ) {
     this.name  = name;
     this.email = email;
   }
 }

  9. Start testing the project:

    10. ⇒

    ⇒
     

    ⇒

    ⇒

    ⇒
     
    New
    session

    ⇒

    ⇒
     

    ⇒
     
    New
    session

    ⇒

    ⇒