apiclient.java

@Override
protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   googleApiClient = createGoogleApiClient();
}

private GoogleApiClient createGoogleApiClient() {
    return new GoogleApiClient.Builder(this).addConnectionCallbacks(this)
            .addOnConnectionFailedListener(this)
            .addApi(Wallet.API, new Wallet.WalletOptions.Builder()
                    .setEnvironment(WalletConstants.ENVIRONMENT_PRODUCTION)
                    .setTheme(WalletConstants.THEME_HOLO_DARK).build()).build();
}

protected void onStart(){
  super.onStart();
  googleApiClient.connect();
}

protected void onStop() {
  googleApiClient.disconnect();
  super.onStop();
}