Google Play Games integrieren (Achievements & Highscores)

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


            findViewById(R.id.highscoresButton).setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    startSignInIntent();
                }
            });
			...
        }


        @Override
        protected void onResume() {
            super.onResume();
            signInSilently();
        }


        private void signInSilently() {
            signInOptions = GoogleSignInOptions.DEFAULT_GAMES_SIGN_IN;
            GoogleSignInAccount account = GoogleSignIn.getLastSignedInAccount(this);
            if (GoogleSignIn.hasPermissions(account, signInOptions.getScopeArray())) {
                // Already signed in.
                // The signed in account is stored in the 'account' variable.
                GoogleSignInAccount signedInAccount = account;
            } else {
                // Haven't been signed-in before. Try the silent sign-in first.
                GoogleSignInClient signInClient = GoogleSignIn.getClient(this, signInOptions);
                signInClient
                        .silentSignIn()
                        .addOnCompleteListener(
                                this,
                                new OnCompleteListener<GoogleSignInAccount>() {
                                    @Override
                                    public void onComplete(@NonNull Task<GoogleSignInAccount> task) {
                                        if (task.isSuccessful()) {
                                            // The signed in account is stored in the task's result.
                                            GoogleSignInAccount signedInAccount = task.getResult();
                                        } else {
                                            // Player will need to sign-in explicitly using via UI.
                                            // See [sign-in best practices](http://developers.google.com/games/services/checklist) for guidance on how and when to implement Interactive Sign-in,
                                            // and [Performing Interactive Sign-in](http://developers.google.com/games/services/android/signin#performing_interactive_sign-in) for details on how to implement
                                            // Interactive Sign-in.
                                        }
                                    }
                                });
            }
        }


        private void startSignInIntent() {
            GoogleSignInClient signInClient = GoogleSignIn.getClient(this,
                    GoogleSignInOptions.DEFAULT_GAMES_SIGN_IN);
            Intent intent = signInClient.getSignInIntent();
            startActivityForResult(intent, 9001);
        }


        @Override
        protected void onActivityResult(int requestCode, int resultCode, Intent data) {
            super.onActivityResult(requestCode, resultCode, data);
            if (requestCode == 9001) {
                GoogleSignInResult result = Auth.GoogleSignInApi.getSignInResultFromIntent(data);
                if (result.isSuccess()) {
                    // The signed in account is stored in the result.
                    GoogleSignInAccount signedInAccount = result.getSignInAccount();
                } else {
                    String message = result.getStatus().getStatusMessage();
                    if (message == null || message.isEmpty()) {
                        message = "Other Error";
                    }
                    new AlertDialog.Builder(this).setMessage(message)
                            .setNeutralButton(android.R.string.ok, null).show();
                }
            }
        }