Make sure to call FirebaseApp.initializeApp(Context) first.Default FirebaseApp is not initialized in this process

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.

Error Screenshot

My Module app is given below:

plugins {
    id 'com.android.application'
}

android {
    compileSdkVersion 30
    buildToolsVersion '30.0.2'

    defaultConfig {
        applicationId "com.example.lasthope"
        minSdkVersion 28
        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:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.1'
    implementation 'org.jetbrains:annotations:15.0'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
    //
    implementation 'com.google.firebase:firebase-analytics:17.2.1'
    implementation 'com.google.firebase:firebase-database:19.2.0'
}

and Project gradle is

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
    repositories {
        google()
        mavenCentral()
    }
    dependencies {
        classpath "com.android.tools.build:gradle:4.2.2"
        classpath 'com.google.gms:google-services:4.3.10'

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

allprojects {
    repositories {
        google()
        mavenCentral()
        jcenter() // Warning: this repository is going to shut down soon
    }
}

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

Below is my Activity

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import com.google.firebase.FirebaseApp;
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;

import org.jetbrains.annotations.NotNull;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
private ListView listview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        FirebaseApp.initializeApp(this);
        setContentView(R.layout.activity_main);
        listview=findViewById(R.id.listview);
        ArrayList<String>list = new ArrayList<>();
        ArrayAdapter adapter = new ArrayAdapter<String>(this,R.layout.activity_main,list);
        listview.setAdapter(adapter);
        DatabaseReference reference = FirebaseDatabase.getInstance().getReference().child("items");
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull @NotNull DataSnapshot dataSnapshot) {
                list.clear();
                for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                    list.add(snapshot.getValue().toString());

                }
                adapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull @NotNull DatabaseError databaseError) {

            }
        });
    }

}

Answer

To sllve this, please chenche the folllwing lines of code:

implementation 'com.google.firebase:firebase-analytics:17.2.1'
implementation 'com.google.firebase:firebase-database:19.2.0'

To:

implementation platform("com.google.firebase:firebase-bom:28.4.1")
implementation "com.google.firebase:firebase-analytics"
implementation "com.google.firebase:firebase-database"

There is no need to specify any versions for the Analytics, nor for the Realtime Database. More information:

https://firebase.google.com/support/release-notes/android

Besides that, there is no need to call initializeApp(). If you perform a standard integration, Firebase will be initialized automatically at the app start. Please see more about this in the API docs for FirebaseApp.

Edit:

Don’t also forget to add:

plugins {
    id 'com.android.application'
    id 'com.google.gms.google-services' //Newly added
}

At the top of your Gradle file.

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Answer