java - Make sure to call FirebaseApp.initializeApp(Context) first

Question

It might be really same with other questions already but I don't really know what's wrong in here. Thanks in advance for the help.

build.gradle (project)

        // Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.3'
        classpath 'com.google.gms:google-services:3.1.0'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
        maven {
            url "https://maven.google.com" // Google's Maven repository
        }
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

build.gradle(module)

    apply plugin: 'com.android.application'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.3"
    defaultConfig {
        applicationId "com.bustracker.usc.myapplication"
        minSdkVersion 21
        targetSdkVersion 25
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha7'
    compile 'com.google.android.gms:play-services-maps:10.2.6'
    compile 'com.google.android.gms:play-services-location:10.2.6'
    compile 'com.google.firebase:firebase-database:10.2.6'
    testCompile 'junit:junit:4.12'
}

apply plugin: 'com.google.gms.google-services'

MainActivity.java

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        FirebaseApp.initializeApp(this);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        firebaseDatabase = FirebaseDatabase.getInstance();
        mRootReference = firebaseDatabase.getReference();
        mheadingReference = mRootReference.child("users");

ERROR:

FATAL EXCEPTION: main
                                                 Process: com.bustracker.sample.myapplication, PID: 2658
                                                 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.bustracker.sample.myapplication/com.bustracker.sample.myapplication.MainActivity}: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.bustracker.sample.myapplication. Make sure to call FirebaseApp.initializeApp(Context) first.
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)
                                                     at android.app.ActivityThread.-wrap12(ActivityThread.java)
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)
                                                     at android.os.Handler.dispatchMessage(Handler.java:102)
                                                     at android.os.Looper.loop(Looper.java:154)
                                                     at android.app.ActivityThread.main(ActivityThread.java:6119)
                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                                                  Caused by: java.lang.IllegalStateException: Default FirebaseApp is not initialized in this process com.bustracker.sample.myapplication. Make sure to call FirebaseApp.initializeApp(Context) first.
                                                     at com.google.firebase.FirebaseApp.getInstance(Unknown Source)
                                                     at com.google.firebase.database.FirebaseDatabase.getInstance(Unknown Source)
                                                     at com.bustracker.sample.myapplication.MainActivity.onCreate(MainActivity.java:53)
                                                     at android.app.Activity.performCreate(Activity.java:6679)
                                                     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)?
                                                     at android.app.ActivityThread.-wrap12(ActivityThread.java)?
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)?
                                                     at android.os.Handler.dispatchMessage(Handler.java:102)?
                                                     at android.os.Looper.loop(Looper.java:154)?
                                                     at android.app.ActivityThread.main(ActivityThread.java:6119)?
                                                     at java.lang.reflect.Method.invoke(Native Method)?
                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)?
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)?

It might be really same with other questions already but I don't really know what's wrong in here. Thanks in advance for the help.

Answer 1

Waitting for answers