使用Firebase崩溃将Google SignIn集成到Android

下面是我得到的错误堆栈 .

FATAL EXCEPTION：main进程：com.example.saisi.agni，PID：4249 java.lang.NullPointerException：尝试调用接口方法'void com.google.firebase.auth.FirebaseAuth $ AuthStateListener.onAuthStateChanged（com.google.firebase .auth.FirebaseAuth）'在android.os.Handler的android.os.Handler.handleCallback（Handler.java:739）的com.google.firebase.auth.FirebaseAuth $ 1.run（未知来源）上的空对象引用 . dispatchMessage（Handler.java:95）位于android.app.Looper.loop（Looper.java:148）的android.app.ActivityThread.main（ActivityThread.java:5539），位于java.lang.reflect.Method.invoke（Native）方法）com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:726）com.android.internal.os.ZygoteInit.main（ZygoteInit.java:616）

我的Google登录代码：

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();
}
}