flutter auth login presenter

login_presenter.dart

class LoginPresenter {
  LoginViewContract _view;
  LoginPresenter(this._view);

  void perform_login() {
    assert(_view != null);
    insta.getToken(<APP_ID>,
        <APP_SECRET>).then((token)
    {
      if (token != null) {
        _view.onLoginScuccess(token.access);
      }
      else {
        _view.onLoginError('Error');
      }
    });
  }
}