📜  Flutter——WebSockets

📅  最后修改于: 2021-09-23 06:26:44             🧑  作者: Mango

WebSockets用于与服务器连接,就像http包一样。它支持与服务器的双向通信,无需轮询。

在本文中,我们将探讨以下与Flutter的WebSockets 相关的主题:

  1. 连接到 WebSocket 服务器
  2. 收听来自服务器的消息。
  3. 向服务器发送数据。
  4. 关闭 WebSocket 连接。

在本文中作为示例,我们将连接到 websocket.org 提供的测试服务器。

连接到 WebSocket 服务器:

web_socket_channel包包含连接到 WebSocket 服务器所需的工具。该包提供了一个WebSocketChannel ,允许用户既可以收听来自服务器的消息,也可以将消息推送到服务器。

在Flutter,使用以下行创建连接到服务器的 WebSocketChannel:

final channel = IOWebSocketChannel.connect('ws://echo.websocket.org');

收听来自服务器的消息:

现在我们已经建立了到服务器的连接,我们将向它发送一条消息并获得与响应相同的消息:

Dart
StreamBuilder(
  stream: widget.channel.stream,
  builder: (context, snapshot) {
    return Text(snapshot.hasData ? '${snapshot.data}' : '');
  },
);


Dart
import 'dart:async';
import 'dart:convert';
  
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
  
Future fetchAlbum() async {
  final response =
  await http.get('https://jsonplaceholder.typicode.com/albums/1');
  
  if (response.statusCode == 200) {
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Loading album failed!');
  }
}
  
Future updateAlbum(String title) async {
  final http.Response response = await http.put(
    'https://jsonplaceholder.typicode.com/albums/1',
    headers: {
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode({
      'title': title,
    }),
  );
  
  if (response.statusCode == 200) {
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Failed to update the album!');
  }
}
  
// the album class
class Album {
  final int id;
  final String title;
  
  Album({this.id, this.title});
  
  factory Album.fromJson(Map json) {
    return Album(
      id: json['id'],
      title: json['title'],
    );
  }
}
  
void main() {
  runApp(MyApp());
}
  
class MyApp extends StatefulWidget {
  MyApp({Key key}) : super(key: key);
  
  @override
  _MyAppState createState() {
    return _MyAppState();
  }
}
  
class _MyAppState extends State {
  final TextEditingController _controller = TextEditingController();
  Future _futureAlbum;
  
  @override
  void initState() {
    super.initState();
    _futureAlbum = getAlbum();
  }
  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Update Data',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: Text('GeeksForGeeks'),
          backgroundColor: Colors.green,
        ),
        body: Container(
          alignment: Alignment.center,
          padding: const EdgeInsets.all(8.0),
          child: FutureBuilder(
            future: _futureAlbum,
            builder: (context, snapshot) {
              if (snapshot.connectionState == ConnectionState.done) {
                if (snapshot.hasData) {
                  return Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: [
                      Text(snapshot.data.title),
                      TextField(
                        controller: _controller,
                        decoration: InputDecoration(hintText: 'Enter Title'),
                      ),
                      RaisedButton(
                        child: Text('Update Data'),
                        onPressed: () {
                          setState(() {
                            _futureAlbum = updateAlbum(_controller.text);
                          });
                        },
                      ),
                    ],
                  );
                } else if (snapshot.hasError) {
                  return Text("${snapshot.error}");
                }
              }
              return CircularProgressIndicator();
            },
          ),
        ),
      ),
    );
  }
}


向服务器发送数据:

要将数据发送到服务器,将 add()消息添加WebSocketChannel提供的接收器,如下所示:

channel.sink.add('Hello Geeks!');

关闭连接:

要关闭与 WebSocket 的连接,请使用以下命令:

channel.sink.close();

完整的源代码:

Dart

import 'dart:async';
import 'dart:convert';
  
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
  
Future fetchAlbum() async {
  final response =
  await http.get('https://jsonplaceholder.typicode.com/albums/1');
  
  if (response.statusCode == 200) {
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Loading album failed!');
  }
}
  
Future updateAlbum(String title) async {
  final http.Response response = await http.put(
    'https://jsonplaceholder.typicode.com/albums/1',
    headers: {
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode({
      'title': title,
    }),
  );
  
  if (response.statusCode == 200) {
    return Album.fromJson(json.decode(response.body));
  } else {
    throw Exception('Failed to update the album!');
  }
}
  
// the album class
class Album {
  final int id;
  final String title;
  
  Album({this.id, this.title});
  
  factory Album.fromJson(Map json) {
    return Album(
      id: json['id'],
      title: json['title'],
    );
  }
}
  
void main() {
  runApp(MyApp());
}
  
class MyApp extends StatefulWidget {
  MyApp({Key key}) : super(key: key);
  
  @override
  _MyAppState createState() {
    return _MyAppState();
  }
}
  
class _MyAppState extends State {
  final TextEditingController _controller = TextEditingController();
  Future _futureAlbum;
  
  @override
  void initState() {
    super.initState();
    _futureAlbum = getAlbum();
  }
  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Update Data',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: Scaffold(
        appBar: AppBar(
          title: Text('GeeksForGeeks'),
          backgroundColor: Colors.green,
        ),
        body: Container(
          alignment: Alignment.center,
          padding: const EdgeInsets.all(8.0),
          child: FutureBuilder(
            future: _futureAlbum,
            builder: (context, snapshot) {
              if (snapshot.connectionState == ConnectionState.done) {
                if (snapshot.hasData) {
                  return Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: [
                      Text(snapshot.data.title),
                      TextField(
                        controller: _controller,
                        decoration: InputDecoration(hintText: 'Enter Title'),
                      ),
                      RaisedButton(
                        child: Text('Update Data'),
                        onPressed: () {
                          setState(() {
                            _futureAlbum = updateAlbum(_controller.text);
                          });
                        },
                      ),
                    ],
                  );
                } else if (snapshot.hasError) {
                  return Text("${snapshot.error}");
                }
              }
              return CircularProgressIndicator();
            },
          ),
        ),
      ),
    );
  }
}

输出:

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