Make sure to call FirebaseApp.initializeApp(Context) first in Android

Question

I am facing this issue and seen some answers on this site but did not get any proper solution.
I have used previous version of Firebase which works fine but when I try to upgrade using Upgradation and update Firebase class to DatabaseReference it shows error and not working.
I am adding my manifest file entire code so please help me to resolve this issue.
Here is my manifest

    <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="firebasechat.com.firebasechat">      <uses-permission android:name="android.permission.INTERNET" />      <application         android:allowBackup="true"         android:name=".Activity.SimpleBlog"         android:icon="@mipmap/ic_launcher"         android:label="@string/app_name"         android:roundIcon="@mipmap/ic_launcher_round"         android:supportsRtl="true"         android:theme="@style/AppTheme">         <activity android:name=".Activity.RegisterActivity">             <intent-filter>                 <action android:name="android.intent.action.MAIN" />                  <category android:name="android.intent.category.LAUNCHER" />             </intent-filter>         </activity>      </application>  </manifest> 

my Module app is given below.

    apply plugin: 'com.android.application'  android {     compileSdkVersion 26     buildToolsVersion "26.0.0"     defaultConfig {         applicationId "firebasechat.com.firebasechat"         minSdkVersion 15         targetSdkVersion 26         versionCode 1         versionName "1.0"         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"          multiDexEnabled  true      }     buildTypes {         release {             minifyEnabled false             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'         }     }     packagingOptions {         exclude 'META-INF/LICENSE'         exclude 'META-INF/LICENSE-FIREBASE.txt'         exclude 'META-INF/NOTICE'     } }    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-v7:26.+' compile 'com.android.volley:volley:1.0.0' compile "com.google.firebase:firebase-database:11.0.0" compile 'com.google.android.gms:play-services:11.0.0' compile 'com.android.support:recyclerview-v7:25.0.0' testCompile 'junit:junit:4.12'     testCompile 'junit:junit:4.12' } 

and Project gradle

    // 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:4.2.0'// Updated version of google service     } } allprojects {     repositories {         jcenter()         maven {             url "https://maven.google.com" // Google's Maven repository         }     } } task clean(type: Delete) {     delete rootProject.buildDir } 

Below is my Activity.

    public class RegisterActivity extends AppCompatActivity {      EditText username, password;     Button registerButton;     String user, pass;       @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_register);          username = (EditText)findViewById(R.id.username);         password = (EditText)findViewById(R.id.password);         registerButton = (Button)findViewById(R.id.registerButton);             FirebaseApp.initializeApp(this);            registerButton.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 user = username.getText().toString();                 pass = password.getText().toString();                       final ProgressDialog pd = new ProgressDialog(RegisterActivity.this);                     pd.setMessage("Loading...");                     pd.show();                      String url = "https://pure-coda-174710.firebaseio.com/users.json";                      StringRequest request = new StringRequest(Request.Method.GET, url, new Response.Listener<String>(){                         @Override                         public void onResponse(String s) {  //                            Firebase reference = new Firebase("https://pure-coda-174710.firebaseio.com/users");                             DatabaseReference reference = FirebaseDatabase.getInstance()                                     .getReferenceFromUrl("https://pure-coda-174710.firebaseio.com/users");                               if(s.equals("null")) {                                 reference.child(user).child("password").setValue(pass);                                 Toast.makeText(RegisterActivity.this, "registration successful", Toast.LENGTH_LONG).show();                             }                             else {                                 try {                                     JSONObject obj = new JSONObject(s);                                      if (!obj.has(user)) {                                         reference.child(user).child("password").setValue(pass);                                         Toast.makeText(RegisterActivity.this, "registration successful", Toast.LENGTH_LONG).show();                                     } else {                                         Toast.makeText(RegisterActivity.this, "username already exists", Toast.LENGTH_LONG).show();                                     }                                  } catch (JSONException e) {                                     e.printStackTrace();                                 }                             }                              pd.dismiss();                         }                      },new Response.ErrorListener(){                         @Override                         public void onErrorResponse(VolleyError volleyError) {                             System.out.println("" + volleyError );                             pd.dismiss();                         }                     });                      RequestQueue rQueue = Volley.newRequestQueue(RegisterActivity.this);                     rQueue.add(request);              }         });     } } 

Answer 1

In your SimpleBlog application class, initialize FirebaseApp in onCreate() method and remove it from RegisterActivity in order to have Firebase initialize into entire application, not just one Activity.

@Override public void onCreate() {     super.onCreate();     FirebaseApp.initializeApp(this); } 

Also add apply plugin: 'com.google.gms.google-services' at the end of app gradle:

dependencies {     .... }  apply plugin: 'com.google.gms.google-services' 

Plugin is required to process your json config from firebase and to avoid dependency collisions. You can read here for more details.

Answer 2

Spent literally a whole day. Finally, this was the solution.

Freaking 0 instead of 1 and you will not have to use the initialize firebaseapp or anything like that.

In Project gradle, use Google services: 4.0.0 and not 4.1.0.

Plus, apply plugin statement at the end is also not necessary in my experience.

(Hoping you have added firebase database from the tools => firebase assistant. Step 1 and step 2 are right and green. )