private static final int RC_SIGN_IN = 123;

private GoogleSignInClient mGoogleSignInClient;

private FirebaseAuth mAuth;

@Override

protected void onStart() {

super.onStart();

FirebaseUser user = mAuth.getCurrentUser();

if (user!=null) {

Intent intent = new Intent(getApplicationContext(), ManHinhChuyenDen.class);

startActivity(intent);

}

}

@Override

protected void onCreate(Bundle savedInstanceState) {

mAuth = FirebaseAuth.getInstance();

DangNhapGoogle();

button.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

signIn();

}

});

}

private void signIn() {

Intent signInIntent = mGoogleSignInClient.getSignInIntent();

startActivityForResult(signInIntent, RC_SIGN_IN);

}

private void DangNhapGoogle() {

GoogleSignInOptions gso = new GoogleSignInOptions

.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)

.requestIdToken(getString(R.string.default_web_client_id))

.requestEmail()

.build();

mGoogleSignInClient = GoogleSignIn.getClient(this, gso);

}

@Override

public void onActivityResult(int requestCode, int resultCode, Intent data){

super.onActivityResult(requestCode, resultCode, data);

if (requestCode == RC_SIGN_IN){

Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);

try {

GoogleSignInAccount account = task.getResult(ApiException.class);

firebaseAuthWithGoogle(account);

} catch (ApiException e) {

Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();

}

}

}

private void firebaseAuthWithGoogle(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()) {

FirebaseUser user = mAuth.getCurrentUser();

Intent intent = new Intent(getApplicationContext(), ManHinhChuyenDen.class);

startActivity(intent);

} else {

Toast.makeText(ManHinhHienTai.this, "Auth failed", Toast.LENGTH_SHORT).show();

}

}

});

}