signin.java

 public class signin extends BaseActivity implements View.OnClickListener, 
    GoogleApiClient.OnConnectionFailedListener {   
    private SignInButton SignIn;
    private static final int REQ_CODE = 9001;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_signin);
        SignIn = (SignInButton) findViewById(R.id.bn_login);

        SignIn.setOnClickListener(this);
        }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent 
    data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == Activity.RESULT_OK) {
            if (requestCode == REQ_CODE) {
                GoogleSignInResult result = 
     Auth.GoogleSignInApi.getSignInResultFromIntent(data);
                if (result.isSuccess()) {
                    GoogleSignInAccount account = result.getSignInAccount();

                    firebaseAuthWithGoogle(account);

                } else {
                    // dismissProgressDialog();
                }
            } else {
                // dismissProgressDialog();
            }
        } else {
            //  dismissProgressDialog();
        }
    }
    @Override
    public void onClick(View v) {

        switch (v.getId()){
            case R.id.bn_login:
                signIn();
                break;

        }
    }

    public void signIn(){

        Intent intent = Auth.GoogleSignInApi.getSignInIntent(mGoogleApiClient);
        startActivityForResult(intent,REQ_CODE);

    }

    private void firebaseAuthWithGoogle(final GoogleSignInAccount account) {
        AuthCredential credential = GoogleAuthProvider.getCredential(account.getIdToken(), null);
        mAuth.signInWithCredential(credential)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        if (task.isSuccessful()) {
                            //Let's create the models quick(I know! it's weird time in this tutorial
                            //To be building it
                            User user = new User();
                            String photoUrl = null;
                            if (account.getPhotoUrl() != null) {
                                user.setPhotoUrl(account.getPhotoUrl().toString());
                            }

                            user.setEmail(account.getEmail());
                            user.setUser(account.getDisplayName());
                            user.setUid(mAuth.getCurrentUser().getUid());

                            FirebaseUtils.getUserRef(account.getEmail().replace(".", ","))
                                    .setValue(user, new DatabaseReference.CompletionListener() {
                                        @Override
                                        public void onComplete(DatabaseError databaseError, DatabaseReference databaseReference) {
                                            mFirebaseUser = mAuth.getCurrentUser();

                                        }
                                    });
                        } else {
                            //  dismissProgressDialog();
                        }
                    }
                });
     }

     }