如何在React Component中导入SignalR？

Question

我已经使用create-react-app搭建了最初的react应用程序。

我的DashBoard组件：

import React, { Component } from 'react';
import { Link } from 'react-router-dom';
import $ from 'jquery';
import 'signalr';

class Dashboard extends Component {
   constructor(props) {    
   super(props);
   var connection = $.hubConnection('http://[address]:[port]');
   var proxy = connection.createHubProxy('[hubname]');   

    // atempt connection, and handle errors
    connection.start()
    .done(function(){ console.log('Now connected, connection ID=' + connection.id); })
    .fail(function(){ console.log('Could not connect'); });
}

  render() {
    return (...);
  }
}

export default Dashboard;

现在，我从SignalR收到以下错误，说未添加jQuery，但已在上一行中将其导入：

错误：找不到jQuery。请确保在SignalR客户端JavaScript文件之前引用jQuery。

如果我注释掉导入“ signalr”；jQuery正确加载，我可以访问$模块内部。为什么会这样？

Answer 1

这就是我们现在（2020 年）使用新包 @microsoft/signalr 执行此操作的方式。我们使用 Redux，但您不必使用 Redux 才能使用此方法。

如果您使用的是@microsoft/signalr 包而不是@aspnet/signalr，那么您可以通过这种方式进行设置。这是我们在 prod 中的工作代码：

import {
  JsonHubProtocol,
  HubConnectionState,
  HubConnectionBuilder,
  LogLevel
} from '@microsoft/signalr';

const isDev = process.env.NODE_ENV === 'development';

const startSignalRConnection = async connection => {
  try {
    await connection.start();
    console.assert(connection.state === HubConnectionState.Connected);
    console.log('SignalR connection established');
  } catch (err) {
    console.assert(connection.state === HubConnectionState.Disconnected);
    console.error('SignalR Connection Error: ', err);
    setTimeout(() => startSignalRConnection(connection), 5000);
  }
};

// Set up a SignalR connection to the specified hub URL, and actionEventMap.
// actionEventMap should be an object mapping event names, to eventHandlers that will
// be dispatched with the message body.
export const setupSignalRConnection = (connectionHub, actionEventMap = {}, getAccessToken) => (dispatch, getState) => {
  const options = {
    logMessageContent: isDev,
    logger: isDev ? LogLevel.Warning : LogLevel.Error,
    accessTokenFactory: () => getAccessToken(getState())
  };
  // create the connection instance
  // withAutomaticReconnect will automatically try to reconnect
  // and generate a new socket connection if needed
  const connection = new HubConnectionBuilder()
    .withUrl(connectionHub, options)
    .withAutomaticReconnect()
    .withHubProtocol(new JsonHubProtocol())
    .configureLogging(LogLevel.Information)
    .build();

  // Note: to keep the connection open the serverTimeout should be
  // larger than the KeepAlive value that is set on the server
  // keepAliveIntervalInMilliseconds default is 15000 and we are using default
  // serverTimeoutInMilliseconds default is 30000 and we are using 60000 set below
  connection.serverTimeoutInMilliseconds = 60000;

  // re-establish the connection if connection dropped
  connection.onclose(error => {
    console.assert(connection.state === HubConnectionState.Disconnected);
    console.log('Connection closed due to error. Try refreshing this page to restart the connection', error);
  });

  connection.onreconnecting(error => {
    console.assert(connection.state === HubConnectionState.Reconnecting);
    console.log('Connection lost due to error. Reconnecting.', error);
  });

  connection.onreconnected(connectionId => {
    console.assert(connection.state === HubConnectionState.Connected);
    console.log('Connection reestablished. Connected with connectionId', connectionId);
  });

  startSignalRConnection(connection);

  connection.on('OnEvent', res => {
    const eventHandler = actionEventMap[res.eventType];
    eventHandler && dispatch(eventHandler(res));
  });

  return connection;
};

然后你会像下面这样调用。请注意，这是一个伪代码。根据您的项目设置，您可能需要以不同的方式调用它。

import { setupSignalRConnection } from 'fileAbove.js';

const connectionHub = '/hub/service/url/events';

export const setupEventsHub = setupSignalRConnection(connectionHub, {
  onMessageEvent: someMethod
}, getAccessToken);

export default () => dispatch => {
  dispatch(setupEventsHub); // dispatch is coming from Redux
};

让我知道它是否通过投票有所帮助。谢谢

Answer 2

更新：请注意，如果您在ReactJS应用程序中使用Redux，则以下解决方案不一定是最佳解决方案。最好将signalR实现为中间件。您可以在此处找到最佳答案。

如果您不使用Redux，或者您仍想在React组件中实现它，请继续阅读：对于使用最新版本的signalR（核心v2.1）的人们，因为jQuery不再是signalR的依赖项，您可以像这样导入：

import * as signalR from '@aspnet/signalr';

然后像这样使用它：

signalR.HubConnectionBuilder()

这是一个例子：

import React, { PureComponent } from 'react';
import { string } from 'prop-types';
import * as signalR from '@aspnet/signalr';

class SignalR extends PureComponent {
  constructor (props) {
    super(props);

    this.connection = null;
    this.onNotifReceived = this.onNotifReceived.bind(this);
  }

  componentDidMount () {
    const protocol = new signalR.JsonHubProtocol();

    const transport = signalR.HttpTransportType.WebSockets;

    const options = {
      transport,
      logMessageContent: true,
      logger: signalR.LogLevel.Trace,
      accessTokenFactory: () => this.props.accessToken,
    };

    // create the connection instance
    this.connection = new signalR.HubConnectionBuilder()
      .withUrl(this.props.connectionHub, options)
      .withHubProtocol(protocol)
      .build();

    this.connection.on('DatabaseOperation', this.onNotifReceived);
    this.connection.on('DownloadSession', this.onNotifReceived);
    this.connection.on('UploadSession', this.onNotifReceived);

    this.connection.start()
      .then(() => console.info('SignalR Connected'))
      .catch(err => console.error('SignalR Connection Error: ', err));
  }

  componentWillUnmount () {
    this.connection.stop();
  }

  onNotifReceived (res) {
    console.info('Yayyyyy, I just received a notification!!!', res);
  }

  render () {
    return <span />;
  };
};

SignalR.propTypes = {
  connectionHub: string.isRequired,
  accessToken: string.isRequired
};

export default SignalR;

Answer 3

我发现Signalr依赖于jQuery。由于某种原因import $ from 'jquery'没有设置window.jQuery。这就是为什么需要明确地做到这一点。

我这样解决了这个问题：

import React, { Component } from 'react';
import { Link } from 'react-router-dom';
import $ from 'jquery';
window.jQuery = $;
require('signalr');

class Dashboard extends Component {
   // .....   
}

export default Dashboard;