【问题标题】：Button stays disabled after changing StreamController<String>.broadcast() to BehaviorSubject<String>()将 StreamController<String>.broadcast() 更改为 BehaviorSubject<String>() 后，按钮保持禁用状态
【发布时间】：2019-04-13 07:52:02
【问题描述】：

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>() 按钮仍处于禁用状态。

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，两个文本字段和提交按钮

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"),
            ),
          );
        },
      );

变化

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 中

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

我希望当逻辑正确时按钮应该保持启用状态，并且在按下按钮之前不应调用该方法

【问题讨论】：

标签： dart flutter stream dart-pub rxdart

【解决方案1】：

在 home.dart 中：

改变这个：

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

到这里

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

解释： bloc.submit 指的是方法，bloc.submit() 指的是该方法的返回值。

您所做的是指的是该方法的返回值，并且由于您没有返回该方法刚刚执行的任何内容，但是由于返回的值为 null，因此按钮仍处于禁用状态。

【讨论】：