showSnackBar ModalScope locked error

import 'package:bloc_pattern/bloc_pattern.dart';
import 'package:flutter/material.dart';
import 'package:mobile/blocs/settings-bloc.dart';
import 'package:mobile/widgets/custom-drawer.dart';
import 'package:mobile/widgets/input_field.dart';

import '../config.dart';
import 'home_screen.dart';

class SetupScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("$APP_TITLE - Ajustes"),
        centerTitle: true,
      ),
      drawer: CustomDrawer(),
      body: SetupForm(),
    );
  }
}

class SetupForm extends StatefulWidget {
  @override
  _SetupFormState createState() => _SetupFormState();
}

class _SetupFormState extends State<SetupForm> {
  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    final bloc = BlocProvider.of<SettingsBloc>(context);

    return SingleChildScrollView(
      child: Container(
        margin: EdgeInsets.all(32),
        child: Form(
          key: _formKey,
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Container(
                width: 160,
                child: Image.asset("images/logo.png"),
              ), // Logo
              SizedBox(height: 32),
              StreamBuilder<SettingsState>(
                stream: bloc.outState,
                builder: (context, snapshot) {
                  if (snapshot.data == SettingsState.SAVED) {
                    bloc.inState.add(SettingsState.DONE);
                    WidgetsBinding.instance.addPostFrameCallback(
                        (_) => _showDialog(context, bloc));
                  }

                  if (snapshot.data != SettingsState.DONE) {
                    return Container(
                      alignment: Alignment.center,
                      margin: EdgeInsets.only(top: 32),
                      child: CircularProgressIndicator(),
                    );
                  }

                  return Column(
                    children: <Widget>[
                      InputField(
                        icon: Icons.local_gas_station,
                        hint: "IP do Concentrador",
                        obscure: false,
                        keyboardType: TextInputType.number,
                        inputFormat: CustomFormatters.FORMAT_IP_ADDRESS,
                        stream: bloc.outEditIP,
                        onChanged: bloc.changeIP,
                      ),
                      InputField(
                        icon: Icons.exit_to_app,
                        hint: "Porta de conexão(771, 1771, 857)",
                        obscure: false,
                        keyboardType: TextInputType.number,
                        inputFormat: CustomFormatters.FORMAT_IP_PORT,
                        stream: bloc.outEditPort,
                        onChanged: bloc.changePort,
                      ),
                      SizedBox(height: 48),
                      StreamBuilder<bool>(
                        stream: bloc.outValidated,
                        builder: (context, snapshot) {
                          return SizedBox(
                            height: 44,
                            child: RaisedButton.icon(
                              disabledColor: Colors.green.withAlpha(140),
                              onPressed: snapshot.hasData
                                  ? () {
                                      bloc.store();
                                    }
                                  : null,
                              icon: Icon(Icons.save, color: Colors.white),
                              label: Text(
                                "Gravar",
                                style: TextStyle(
                                  fontSize: 18.0,
                                  color: Colors.white,
                                ),
                              ),
                              color: Colors.green,
                            ),
                          );
                        },
                      ),
                    ],
                  );
                },
              ),
            ],
          ),
        ),
      ),
    );
  }

  void _showDialog(BuildContext context, SettingsBloc bloc) {
    Scaffold.of(context).showSnackBar(SnackBar(
      content: Text('Dados de conexão gravados com sucesso!'),
      duration: Duration(days: 1),
      backgroundColor: Colors.black87,
      action: SnackBarAction(
        textColor: Colors.yellow,
        label: 'Ok',
        onPressed: () async {
          bloc.inPage.add(0);
          await Navigator.of(context).push(
            MaterialPageRoute(builder: (context) => HomeScreen()),
          );
        },
      ),
    ));
  }
}