Default FirebaseApp is not initialized in this process... error

[SandroSF]

this error is popping up for me when I open the app "Default FirebaseApp is not initialized in this process com.example.app. Make sure to call FirebaseApp.initializeApp(Context) first." only I have already initialized, I do not know why it is not working




package sandro.sf.testar;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

import com.google.android.gms.auth.api.Auth;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.SignInButton;
import com.google.android.gms.common.api.ApiException;
import com.google.android.gms.common.api.GoogleApi;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.FirebaseApp;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.auth.GoogleAuthProvider;

public class MainActivity extends AppCompatActivity {

    private SignInButton mGoogleBtn;

   private static final int RC_SIGN_IN = 1;

     private GoogleApiClient mGoogleSignInClient;

    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getSupportActionBar().hide();
        setContentView(R.layout.activity_act_inicial);

        FirebaseApp.initializeApp(this);

        mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {

                if (firebaseAuth.getCurrentUser() != null) {

                    startActivity(new Intent(MainActivity.this, AcountActivity.class));

                }

            }
        };



        try {


            mAuth = FirebaseAuth.getInstance();

        }catch (Exception e){

            Toast.makeText(MainActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();


        }

    }

}