使用RxDart从Stream发送AlertDialog

Question

我是Flutter的新手，我试图在BLoC类（doRegister方法）中进行验证后提出一个AlertDialog，但实际上我不知道如何显示Dialog，有人可以帮我一些提示吗。我被困在这里。

我是否必须始终在StreamBuilder中创建AlertDialog小部件？还是可以仅在需要时创建（在验证之后），以及如何为对话框传递消息？

class RegisterBloc implements BaseBloc {
     BehaviorSubject<String> _emailSubject = 
     BehaviorSubject.seeded('');
     BehaviorSubject<String> _userSubject = BehaviorSubject.seeded('');
     BehaviorSubject<String> _phoneSubject = 
     BehaviorSubject.seeded('');
     BehaviorSubject<bool> _termsSubject = 
     BehaviorSubject.seeded(false);
     BehaviorSubject<bool> _isLoadingSubject = 
     BehaviorSubject.seeded(false);

     // Streams and Sinks....

     void doRegister() {
        if (!_selectedCountrySubject.hasValue ||
           _selectedCountrySubject.value.isEmpty ||
           _emailSubject.value.isEmpty ||
           _userSubject.value.isEmpty ||
           _phoneSubject.value.isEmpty) {
           print('Empty');
           // HERE I wanna show the Alert Message.
      }

      // Test to present a Progress
      updateLoading(!_isLoadingSubject.value);
      print('End Register');
   }
}

这是我的StatefulWidget状态类

@override
  Widget build(BuildContext context) {
    const _sizedBox = SizedBox(height: 12.0);

return Scaffold(
    appBar: AppBar(
      title: Text(
        Translations.of(context).text('app_title'),
        style: Theme.of(context).textTheme.display1,
      ),
    ),
    body: Stack(
      children: <Widget>[
        Column(
          children: <Widget>[
            Expanded(
              child: ListView(
                shrinkWrap: true,
                padding: EdgeInsets.all(15.0),
                children: <Widget>[
                  Column(
                    children: <Widget>[
                      _countryDropDown(context),
                      _sizedBox,
                      _emailTextField(context),
                      _sizedBox,
                      _userTextField(context),
                      _sizedBox,
                      _phoneTextField(context),
                      _sizedBox,
                      _companyCode(context),
                      _sizedBox,
                      _inviteCodeTextField(context),
                      _sizedBox,
                      _termsAndConditionsCheck(),
                    ],
                  ),
                ],
              ),
            ),
            Padding(
              padding: const EdgeInsets.only(bottom: 10),
              child: _bottomButtons(),
            ),
          ],
        ),
        _loadingIndicator(),
      ],
    ),
}