google-app-engine - Rx.combineLatest2无法正常工作

Question

我是使用 flutter 的新手。我试图在flutter中创建一些示例应用程序以创建自己的应用程序。我发现了带有团块模式的 flutter 打中很好的应用程序。请参阅以下 link 。

这只是一个登录页面。表单中有一个带有验证的电子邮件和密码文本框。一个验证器用于电子邮件，另一个验证器用于密码长度。表单中有一个提交按钮，最初已禁用，如果电子邮件和密码成功验证，则启用提交按钮。它使用带有 rxdart 软件包的块模式架构。

我在提交按钮验证方面遇到问题，在输入电子邮件和密码字段后，未启用按钮字段。

按钮验证码

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

请参见下面的代码。

main.dart

import 'package:bloc_login/pagetwo.dart';
import 'package:flutter/material.dart';
import 'package:bloc_login/bloc.dart';
import 'package:flutter/rendering.dart';

 void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
 @override
  Widget build(BuildContext context) {
return MaterialApp(
  home: MyHomePage(title: 'Flutter Demo Home Page'),
  title: 'Flutter Demo',
  theme: ThemeData(
    primarySwatch: Colors.teal,
  ),
  debugShowCheckedModeBanner: false,
);
}
}

class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
 @override
_MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
 changethePage(BuildContext context) {
Navigator.of(context)
    .push(MaterialPageRoute(builder: (context) => PageTwo()));
  }

 @override
   Widget build(BuildContext context) {
final bloc = Bloc();

return Scaffold(
  appBar: AppBar(
    title: Text("Bloc pattern"),
  ),
  body: SingleChildScrollView(
    child: Container(
      height: MediaQuery.of(context).size.height,
      padding: EdgeInsets.all(16),
      child: Column(
        mainAxisSize: MainAxisSize.max,
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          StreamBuilder<String>(
            stream: bloc.email,
            builder: (context, snapshot) => TextField(
              onChanged: bloc.emailChanged,
              keyboardType: TextInputType.emailAddress,
              decoration: InputDecoration(
                  border: OutlineInputBorder(),
                  hintText: "Enter Email",
                  labelText: "Email",
                  errorText: snapshot.error),
            ),
          ),
          SizedBox(
            height: 20,
          ),
          StreamBuilder<String>(
            stream: bloc.password,
            builder: (context, snapshot) => TextField(
              onChanged: bloc.passwordChanged,
              keyboardType: TextInputType.text,
              obscureText: true,
              decoration: InputDecoration(
                  border: OutlineInputBorder(),
                  hintText: "Enter password",
                  labelText: "Password",
                  errorText: snapshot.error),
            ),
          ),
          SizedBox(
            height: 20,
          ),
          StreamBuilder<bool>(
              stream: bloc.submitCheck,
              builder: (context, snapshot) => RaisedButton(
                    color: Colors.tealAccent,
                    onPressed: (snapshot.data != null)
                        ? () => changethePage(context)
                        : null,
                    child: Text("Submit"),
                  ))
        ],
      ),
    ),
  ),
);
}
}

bloc.dart

import 'dart:async';
import 'package:bloc_login/validator.dart';
import 'package:rxdart/rxdart.dart';

class Bloc extends Object with Validators implements BaseBloc {
final _emailController = StreamController<String>();
final _passwordController = StreamController<String>();

Function(String) get emailChanged => _emailController.sink.add;
Function(String) get passwordChanged => _passwordController.sink.add;

Stream<String> get email => _emailController.stream.transform(emailValidator);
Stream<String> get password =>
  _passwordController.stream.transform(passwordValidator);

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

@override
void dispose() {
_emailController.close();
_passwordController.close();
}
}

 abstract class BaseBloc {
   void dispose();
}

validator.dart

import 'dart:async';

mixin Validators {
 var emailValidator =
  StreamTransformer<String, String>.fromHandlers(handleData: (email, sink) {
if (email.contains("@")) {
  sink.add(email);
} else {
  sink.addError("Email is not valid.");
}
});

var passwordValidator = StreamTransformer<String, String>.fromHandlers(
  handleData: (password, sink) {
if (password.length > 4) {
  sink.add(password);
} else {
  sink.addError("Password length should be greater than 4.");
}
});
}

请指教。

Answer 1

Combinelatest2很好，问题是您在每次重建中都创建了一个新的块。

因此，请在initState方法中创建块，并在StatefulWidget的dispose方法中处理该块。

而且您的StreamController的Stream仅支持一个订阅者，因此，如果您希望Stream的StreamController可以被监听多次，则需要将其作为广播流，其中一种方法是使用StreamController .broadcast ()构造函数。

P.D.如果使用bloc模式创建表单，则可以检查flutter_form_bloc，它可以节省大量代码。

从Dart 2.1 you don't need to extend an object to use a mixin开始

class Bloc with Validators implements BaseBloc {
  final _emailController = StreamController<String>.broadcast();
  final _passwordController = StreamController<String>.broadcast();
  //...
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Bloc _bloc;

  @override
  void initState() {
    super.initState();
    _bloc = Bloc();
  }

  @override
  void dispose() {
    _bloc.dispose();
    super.dispose();
  }

  changethePage(BuildContext context) {
    Navigator.of(context)
        .push(MaterialPageRoute(builder: (context) => PageTwo()));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Bloc pattern"),
      ),
      body: SingleChildScrollView(
        child: Container(
          height: MediaQuery.of(context).size.height,
          padding: EdgeInsets.all(16),
          child: Column(
            mainAxisSize: MainAxisSize.max,
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              StreamBuilder<String>(
                stream: _bloc.email,
                builder: (context, snapshot) => TextField(
                  onChanged: _bloc.emailChanged,
                  keyboardType: TextInputType.emailAddress,
                  decoration: InputDecoration(
                      border: OutlineInputBorder(),
                      hintText: "Enter Email",
                      labelText: "Email",
                      errorText: snapshot.error),
                ),
              ),
              SizedBox(
                height: 20,
              ),
              StreamBuilder<String>(
                stream: _bloc.password,
                builder: (context, snapshot) => TextField(
                  onChanged: _bloc.passwordChanged,
                  keyboardType: TextInputType.text,
                  obscureText: true,
                  decoration: InputDecoration(
                      border: OutlineInputBorder(),
                      hintText: "Enter password",
                      labelText: "Password",
                      errorText: snapshot.error),
                ),
              ),
              SizedBox(
                height: 20,
              ),
              StreamBuilder<bool>(
                  stream: _bloc.submitCheck,
                  builder: (context, snapshot) => RaisedButton(
                        color: Colors.tealAccent,
                        onPressed: (snapshot.data != null)
                            ? () => changethePage(context)
                            : null,
                        child: Text("Submit"),
                      ))
            ],
          ),
        ),
      ),
    );
  }
}