Flutter：WebSocket封装-实现心跳、重连机制

前言Permalink
Flutter简介

Flutter 是 Google推出并开源的移动应用开发框架，主打跨平台、高保真、高性能。开发者可以通过 Dart语言开发 App，一套代码同时运行在 iOS 和 Android平台。 Flutter提供了丰富的组件、接口，开发者可以很快地为 Flutter添加 native扩展。同时 Flutter还使用 Native引擎渲染视图，这无疑能为用户提供良好的体验。

WebSocket简介

Http协议是无状态的，只能由客户端主动发起，服务端再被动响应，服务端无法向客户端主动推送内容，并且一旦服务器响应结束，链接就会断开(见注解部分)，所以无法进行实时通信。WebSocket协议正是为解决客户端与服务端实时通信而产生的技术，现在已经被主流浏览器支持，所以对于Web开发者来说应该比较熟悉了，Flutter也提供了专门的包来支持WebSocket协议。

注意：Http协议中虽然可以通过keep-alive机制使服务器在响应结束后链接会保持一段时间，但最终还是会断开，keep-alive机制主要是用于避免在同一台服务器请求多个资源时频繁创建链接，它本质上是支持链接复用的技术，而并非用于实时通信，读者需要知道这两者的区别。

WebSocket协议本质上是一个基于tcp的协议，它是先通过HTTP协议发起一条特殊的http请求进行握手后，如果服务端支持WebSocket协议，则会进行协议升级。WebSocket会使用http协议握手后创建的tcp链接，和http协议不同的是，WebSocket的tcp链接是个长链接（不会断开），所以服务端与客户端就可以通过此TCP连接进行实时通信。有关WebSocket协议细节，读者可以看RFC文档，下面我们重点看看Flutter中如何使用WebSocket。

话不多说，直接撸代码Permalink
添加依赖：

web_socket_channel: ^1.1.0 # WebSocket
新建web_socket_utility.dart工具类：

import 'dart:async';import 'package:web_socket_channel/io.dart';
import 'package:web_socket_channel/web_socket_channel.dart';/// WebSocket地址
const String _SOCKET_URL = 'ws://121.40.165.18:8800';/// WebSocket状态
enum SocketStatus {SocketStatusConnected, // 已连接SocketStatusFailed, // 失败SocketStatusClosed, // 连接关闭
}class WebSocketUtility {/// 单例对象static WebSocketUtility _socket;/// 内部构造方法，可避免外部暴露构造函数，进行实例化WebSocketUtility._();/// 获取单例内部方法factory WebSocketUtility() {// 只能有一个实例if (_socket == null) {_socket = new WebSocketUtility._();}return _socket;}IOWebSocketChannel _webSocket; // WebSocketSocketStatus _socketStatus; // socket状态Timer _heartBeat; // 心跳定时器num _heartTimes = 3000; // 心跳间隔(毫秒)num _reconnectCount = 60; // 重连次数，默认60次num _reconnectTimes = 0; // 重连计数器Timer _reconnectTimer; // 重连定时器Function onError; // 连接错误回调Function onOpen; // 连接开启回调Function onMessage; // 接收消息回调/// 初始化WebSocketvoid initWebSocket({Function onOpen, Function onMessage, Function onError}) {this.onOpen = onOpen;this.onMessage = onMessage;this.onError = onError;openSocket();}/// 开启WebSocket连接void openSocket() {closeSocket();_webSocket = IOWebSocketChannel.connect(_SOCKET_URL);print('WebSocket连接成功: $_SOCKET_URL');// 连接成功，返回WebSocket实例_socketStatus = SocketStatus.SocketStatusConnected;// 连接成功，重置重连计数器_reconnectTimes = 0;if (_reconnectTimer != null) {_reconnectTimer.cancel();_reconnectTimer = null;}onOpen();// 接收消息_webSocket.stream.listen((data) => webSocketOnMessage(data),onError: webSocketOnError, onDone: webSocketOnDone);}/// WebSocket接收消息回调webSocketOnMessage(data) {onMessage(data);}/// WebSocket关闭连接回调webSocketOnDone() {print('closed');reconnect();}/// WebSocket连接错误回调webSocketOnError(e) {WebSocketChannelException ex = e;_socketStatus = SocketStatus.SocketStatusFailed;onError(ex.message);closeSocket();}/// 初始化心跳void initHeartBeat() {destroyHeartBeat();_heartBeat =new Timer.periodic(Duration(milliseconds: _heartTimes), (timer) {sentHeart();});}/// 心跳void sentHeart() {sendMessage('{"module": "HEART_CHECK", "message": "请求心跳"}');}/// 销毁心跳void destroyHeartBeat() {if (_heartBeat != null) {_heartBeat.cancel();_heartBeat = null;}}/// 关闭WebSocketvoid closeSocket() {if (_webSocket != null) {print('WebSocket连接关闭');_webSocket.sink.close();destroyHeartBeat();_socketStatus = SocketStatus.SocketStatusClosed;}}/// 发送WebSocket消息void sendMessage(message) {if (_webSocket != null) {switch (_socketStatus) {case SocketStatus.SocketStatusConnected:print('发送中：' + message);_webSocket.sink.add(message);break;case SocketStatus.SocketStatusClosed:print('连接已关闭');break;case SocketStatus.SocketStatusFailed:print('发送失败');break;default:break;}}}/// 重连机制void reconnect() {if (_reconnectTimes < _reconnectCount) {_reconnectTimes++;_reconnectTimer =new Timer.periodic(Duration(milliseconds: _heartTimes), (timer) {openSocket();});} else {if (_reconnectTimer != null) {print('重连次数超过最大次数');_reconnectTimer.cancel();_reconnectTimer = null;}return;}}
}使用方法Permalink
import 'package:my_app/utils/web_socket_utility.dart';WebSocketUtility().initWebSocket(onOpen: () {WebSocketUtility().initHeartBeat();
}, onMessage: (data) {print(data);
}, onError: (e) {print(e);
});

转自：https://ricardolsw.github.io/blog/Flutter-WebSocket%E5%B0%81%E8%A3%85-%E5%AE%9E%E7%8E%B0%E5%BF%83%E8%B7%B3-%E9%87%8D%E8%BF%9E%E6%9C%BA%E5%88%B6/

更新dart版本后的代码：

import 'dart:async';import 'package:web_socket_channel/io.dart';
import 'package:web_socket_channel/web_socket_channel.dart';
import 'package:kkview_kuaichuan/config.dart';
/// WebSocket状态
enum SocketStatus {socketStatusConnected, // 已连接socketStatusFailed, // 失败socketStatusClosed, // 连接关闭
}class WebSocketUtility {/// 单例对象static final WebSocketUtility _socket = WebSocketUtility._internal();/// 内部构造方法，可避免外部暴露构造函数，进行实例化WebSocketUtility._internal();/// 获取单例内部方法factory WebSocketUtility() {return _socket;}late WebSocketChannel _webSocket; // WebSocketSocketStatus? _socketStatus; // socket状态Timer? _heartBeat; // 心跳定时器final int _heartTimes = 30000; // 心跳间隔(毫秒)final int _reconnectCount = 2; // 重连次数，默认60次int _reconnectTimes = 0; // 重连计数器Timer? _reconnectTimer; // 重连定时器late Function onError; // 连接错误回调late Function onOpen; // 连接开启回调late Function onMessage; // 接收消息回调/// 初始化WebSocketvoid initWebSocket({required Function onOpen, required Function onMessage, required Function onError}) {this.onOpen = onOpen;this.onMessage = onMessage;this.onError = onError;openSocket();}/// 开启WebSocket连接void openSocket() {// closeSocket();_webSocket = WebSocketChannel.connect(Uri.parse(SIGNALSERVERURL));print('WebSocket连接成功: $SIGNALSERVERURL');// 连接成功，返回WebSocket实例_socketStatus = SocketStatus.socketStatusConnected;// 连接成功，重置重连计数器_reconnectTimes = 0;if (_reconnectTimer != null) {_reconnectTimer?.cancel();_reconnectTimer = null;}onOpen();// 接收消息_webSocket.stream.listen((data) => webSocketOnMessage(data),onError: webSocketOnError, onDone: webSocketOnDone);}/// WebSocket接收消息回调webSocketOnMessage(data) {onMessage(data);}/// WebSocket关闭连接回调webSocketOnDone() {print('webSocketOnDone closed');_socketStatus = SocketStatus.socketStatusClosed;reconnect();}/// WebSocket连接错误回调webSocketOnError(e) {WebSocketChannelException ex = e;_socketStatus = SocketStatus.socketStatusFailed;onError(ex.message);closeSocket();}/// 初始化心跳void initHeartBeat() {destroyHeartBeat();_heartBeat =Timer.periodic(Duration(milliseconds: _heartTimes), (timer) {sentHeart();});}/// 心跳void sentHeart() {sendMessage('{"module": "HEART_CHECK", "message": "请求心跳"}');}/// 销毁心跳void destroyHeartBeat() {if (_heartBeat != null) {_heartBeat?.cancel();_heartBeat = null;}}/// 关闭WebSocketvoid closeSocket() {print('WebSocket连接关闭');_webSocket.sink.close();destroyHeartBeat();_socketStatus = SocketStatus.socketStatusClosed;}/// 发送WebSocket消息void sendMessage(message) {switch (_socketStatus) {case SocketStatus.socketStatusConnected:print('发送中：$message');_webSocket.sink.add(message);break;case SocketStatus.socketStatusClosed:print('连接已关闭');break;case SocketStatus.socketStatusFailed:print('发送失败');break;default:break;}}/// 重连机制void reconnect() {if (_reconnectTimes < _reconnectCount) {_reconnectTimes++;_reconnectTimer =Timer.periodic(Duration(milliseconds: _heartTimes), (timer) {openSocket();});} else {if (_reconnectTimer != null) {print('重连次数超过最大次数');_reconnectTimer?.cancel();_reconnectTimer = null;}return;}}get socketStatus => _socketStatus;get webSocketCloseCode => _webSocket.closeCode;}