Integrating Google SignIn to Android using Firebase crashes

Question

Below is the error stack that I'm getting.

FATAL EXCEPTION: main Process: com.example.saisi.agni, PID: 4249 java.lang.NullPointerException: Attempt to invoke interface method 'void com.google.firebase.auth.FirebaseAuth$AuthStateListener.onAuthStateChanged(com.google.firebase.auth.FirebaseAuth)' on a null object reference at com.google.firebase.auth.FirebaseAuth$1.run(Unknown Source) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5539) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

My Google SignIn Code:

import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.view.View;
import android.widget.Toast;

import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.auth.api.signin.GoogleSignInResult;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.ResultCallback;
import com.google.android.gms.common.api.Status;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.android.gms.auth.api.Auth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.auth.GoogleAuthProvider;


public class GoogleSignIn extends MainActivity implements
GoogleApiClient.OnConnectionFailedListener, View.OnClickListener {

private FirebaseAuth mFirebaseAuth;
private FirebaseAuth.AuthStateListener mAuthStateListener;
private GoogleApiClient mGoogleApiClient;

public final static int RC_SIGN_IN = 1;

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

    findViewById(R.id.GoogleSignInButton);
    GoogleSignInOptions googleSignInOptions = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
            .requestIdToken(getString(R.string.default_web_client_id))
            .requestEmail()
            .build();

    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .enableAutoManage(this,this)
            .addApi(Auth.GOOGLE_SIGN_IN_API, googleSignInOptions)
            .build();

    mFirebaseAuth = FirebaseAuth.getInstance();

    mAuthStateListener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            FirebaseUser user = mFirebaseAuth.getCurrentUser();
            if (user!= null){
                //user is signed in
                startActivity(new Intent(getApplicationContext(),UserProfile.class));
                finish();
            }
            else {
                //user is signed out
                finish();
                startActivity(new Intent(getApplicationContext(),MainActivity.class));
            }
        }
    };
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == RC_SIGN_IN){
        GoogleSignInResult result = Auth.GoogleSignInApi.getSignInResultFromIntent(data);
        if (result.isSuccess()) {
            // Google Sign In was successful, authenticate with Firebase
            GoogleSignInAccount account = result.getSignInAccount();
            firebaseAuthWithGoogle(account);
        }
    }

}

private void firebaseAuthWithGoogle(GoogleSignInAccount acct) {
    AuthCredential credential = GoogleAuthProvider.getCredential(acct.getIdToken(), null);
    mFirebaseAuth.signInWithCredential(credential)
            .addOnCompleteListener(GoogleSignIn.this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
               if(task.isSuccessful()){
                   Toast.makeText(getApplicationContext(),"User Registeration Successful",Toast.LENGTH_SHORT).show();
                   startActivity(new Intent(getApplicationContext(),MoreUserDetails.class));
                   finish();
               }
               else
               {
                   Toast.makeText(getApplicationContext(), "User registeration failed please try again",Toast.LENGTH_SHORT );
               }
                }
            });
}
private void signIn() {
    Intent signInIntent = Auth.GoogleSignInApi.getSignInIntent(mGoogleApiClient);
    startActivityForResult(signInIntent, RC_SIGN_IN);
}

private void signOut() {
    // Firebase sign out
    mFirebaseAuth.signOut();

    // Google sign out
    Auth.GoogleSignInApi.signOut(mGoogleApiClient).setResultCallback(
            new ResultCallback<Status>() {
                @Override
                public void onResult(@NonNull Status status) {
                    updateUI(null);
                }
            });
}
private void updateUI(FirebaseUser user) {
    if (user != null) {

}}



@Override
public void onClick(View v) {
    int i = v.getId();
    if (i == R.id.GoogleSignInButton) {
        signIn();
    }
}

@Override
public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
    Toast.makeText(this, "Google Play Services error.", Toast.LENGTH_SHORT).show();
}
}

Answer 1

In onAuthStateChanged you're trying to getCurrentUser with mFirebaseAuth. You should change it to use firebaseAuth:

FirebaseUser user = firebaseAuth.getCurrentUser();