更改StreamController后按钮保持禁用状态 .broadcast（）到BehaviorSubject （）

Question

我使用Streams和rxdart进行表单验证。当我使用StreamController<String>.broadcast()时，按钮启用 - 禁用逻辑工作正常。

即使逻辑正确，将其更改为BehaviorSubject<String>()按钮也会保持禁用状态。

bloc.dart

import 'dart:async';

import 'package:login_validation_with_bloc/blocs/validator.dart';
import 'package:rxdart/rxdart.dart';

class Bloc with Validator 
  final _emailController = StreamController<String>.broadcast();
  final _passwordController = StreamController<String>.broadcast();

  Stream<String> get email => _emailController.stream.transform(validateEmail);

  Stream<String> get password =>
      _passwordController.stream.transform(validatePassword);

  Stream<bool> get validForm =>
      Observable.combineLatest2(email, password, (e, p) => true);

  Function(String) get changeEmail => _emailController.sink.add;

  Function(String) get changePassword => _passwordController.sink.add;

  dispose() 
    _emailController.close();
    _passwordController.close();
  


final bloc = Bloc();

home.dart, Two TextFields and Submit button

Widget emailTextField(context, Bloc bloc) => StreamBuilder(
        stream: bloc.email,
        builder: (context, snapshot) => TextField(
              decoration: InputDecoration(
                  labelText: "Email",
                  hintText: "Enter your email address",
                  errorText: snapshot.error,
                  border: UnderlineInputBorder()),
              keyboardType: TextInputType.emailAddress,
              onChanged: bloc.changeEmail,
            ),
      );

  Widget passwordTextField(context, Bloc bloc) => StreamBuilder(
        stream: bloc.password,
        builder: (context, snapshot) => TextField(
              decoration: InputDecoration(
                  labelText: "Password",
                  hintText: "Enter your password",
                  errorText: snapshot.error,
                  border: UnderlineInputBorder()),
              keyboardType: TextInputType.text,
              obscureText: true,
              onChanged: bloc.changePassword,
            ),
      );

  Widget submitButton(context, Bloc bloc) => StreamBuilder(
        stream: bloc.validForm,
        builder: (context, snapshot) 
          return Container(
            child: RaisedButton(
              color: Colors.blue,
              disabledColor: Colors.grey,
              textColor: Colors.white,
              disabledTextColor: Colors.white70,
              onPressed: snapshot.hasData && !snapshot.hasError
                  ? () 
                      print("Submit button pressed");
                    
                  : null,
              elevation: 5,
              disabledElevation: 0,
              child: Text("Submit"),
            ),
          );
        ,
      );

Changes

在bloc.dart中

final _emailController = BehaviorSubject<String>();
final _passwordController = BehaviorSubject<String>();

submit() 
    final validEmail = _emailController.value;
    final validPassword = _passwordController.value;

    print("\n\tEmail: $validEmail\n\tPassword: $validPassword");

在home.dart

snapshot.hasData && !snapshot.hasError ? bloc.submit() : null,

我希望按钮在逻辑正确时保持启用状态，并且除非按下按钮，否则不应调用该方法