SignalR hub configuration in React application

18 Nov 201817 minutes to read

Overview

This guide explains how to configure SignalR Hub in a React application for real-time collaborative diagram editing.

Prerequisites

• System requirements for React components

How to create React sample

To create a React application, follow the steps outlined in the React Getting Started documentation.

How to add packages in the React application

Open the terminal and install the following packages using npm.

• @microsoft/signalr
• @syncfusion/ej2-react-diagrams

Configure SignalR service in React application

To enable real-time collaboration, configure SignalR HubConnection in your React component as follows:

• Initialize the HubConnection within a useEffect hook and start it by calling start().
• Connect to the /diagramHub endpoint with WebSocket transport skipNegotiation: true and enable automatic reconnect to handle transient network issues.
• Subscribe to the OnConnectedAsync callback to receive the unique connection ID, confirming a successful handshake with the server.
• Join a SignalR group by calling JoinDiagram(roomName) after connecting. This ensures updates are shared only with users in the same diagram session.
• Refer to Create React Simple Diagram

import React, { useEffect, useRef, useState } from 'react';
import * as signalR from '@microsoft/signalr';

const DiagramComponent = () => {
  const connectionRef = useRef<signalR.HubConnection | null>(null);
  const [roomName] = useState('Syncfusion');

  useEffect(() => {
    const initializeSignalRConnection = () => {
      if (connectionRef.current === null) {
        // Create connection
        const connection = new signalR.HubConnectionBuilder()
          .withUrl('<<Your ServiceURL>>', {
            skipNegotiation: true,
            transport: signalR.HttpTransportType.WebSockets
          })
          .withAutomaticReconnect()
          .build();

        // Triggered when the connection to the SignalR Hub is successfully established
        connection.on('OnConnectedAsync', (id: string) => {
          onConnectedAsync(id);
        });

        // Start the connection
        connection.start()
          .then(() => {
            console.log('Connected to SignalR Hub');
            setIsConnected(true);
            connectionRef.current = connection;
          })
          .catch((error: Error) => {
            console.error('Connection failed:', error);
          });
      }
    };

    initializeSignalRConnection();

    return () => {
      if (connectionRef.current && connectionRef.current.state === signalR.HubConnectionState.Connected) {
        connectionRef.current.stop();
      }
    };
  }, []);

  const onConnectedAsync = (id: string) => {
    if (id && id.length > 0) {
      console.log('Connection ID:', id);
      // Join the room after connection is established
      connectionRef.current?.invoke('JoinDiagram', roomName)
        .catch((error: Error) => {
          console.error('JoinDiagram failed:', error);
        });
    }
  };

  return (
    <div>
      {/* Diagram component will be added here */}
    </div>
  );
};

export default DiagramComponent;

Notes:

• Use a unique roomName per diagram (e.g., a diagram ID) to isolate sessions.
• If WebSockets may be unavailable, remove SkipNegotiation so SignalR can fall back to SSE or Long Polling.
• Consider handling reconnecting/disconnected states in the UI and securing the connection with authentication, if required.

Sending and applying real-time diagram changes

• The React Diagram component triggers the historyChange event whenever the diagram is modified (e.g., add, delete, move, resize, or edit nodes/connectors).
• Use getDiagramUpdates to produce a compact set of incremental updates (JSON-formatted changes) representing just the changes, not the entire diagram.
• Send these changes to the hub method BroadcastToOtherUsers, which relays them to all users joined to the same SignalR group (room).
• Each remote user listens for ReceiveData and applies the incoming changes with setDiagramUpdates, keeping their view synchronized without reloading the full diagram.
• Enable the enableCollaborativeEditing property on the diagram to treat multi-step edits (like drag/resize sequences or batch changes) as a single operation.

import React, { useEffect, useRef, useState } from 'react';
import { DiagramComponent } from '@syncfusion/ej2-react-diagrams';
import * as signalR from '@microsoft/signalr';

const DiagramCollaborativeComponent = () => {
  const diagramRef = useRef<DiagramComponent>(null);
  const connectionRef = useRef<signalR.HubConnection | null>(null);
  const [roomName] = useState('Syncfusion');
  const [diagramId] = useState('diagram');

  useEffect(() => {
    // Initialize SignalR connection 
    const initializeConnection = async () => {
      if (connectionRef.current === null) {
        const connection = new signalR.HubConnectionBuilder()
          .withUrl('<<Your ServiceURL>>', {
            skipNegotiation: true,
            transport: signalR.HttpTransportType.WebSockets
          })
          .withAutomaticReconnect()
          .build();

        // Listen for remote changes from other users
        connection.on('ReceiveData', (diagramChanges: string[]) => {
          if (diagramChanges && diagramChanges.length > 0) {
            if (diagramRef.current && diagramRef.current.setDiagramUpdates) {
              diagramRef.current.setDiagramUpdates(diagramChanges);
            }
          }
        });

        await connection.start()
          .then(() => {
            console.log('Connected to SignalR Hub');
            connectionRef.current = connection;
          })
          .catch((error: Error) => {
            console.error('Connection failed:', error);
          });
      }
    };

    initializeConnection();

    return () => {
      if (connectionRef.current && connectionRef.current.state === signalR.HubConnectionState.Connected) {
        connectionRef.current.stop();
      }
    };
  }, []);

  const onHistoryChange = async (args: any) => {
    if (args && diagramRef.current && diagramRef.current.getDiagramUpdates) {
      // Get diagram updates (incremental changes) and send to hub
      const diagramChanges = diagramRef.current.getDiagramUpdates(args);
      
      // When enableCollaborativeEditing is enabled, retrieve diagramChanges only after the group action completes.
      if (diagramChanges && diagramChanges.length > 0) {
        // Send changes to the SignalR Hub for broadcasting
        if (connectionRef.current && connectionRef.current.state === signalR.HubConnectionState.Connected) {
          connectionRef.current.invoke('BroadcastToOtherUsers', diagramChanges, roomName)
            .catch((err: Error) => {
              console.error('Send failed:', err);
            });
        }
      }
    }
  };

  return (
    <DiagramComponent
      ref={diagramRef}
      id={diagramId}
      width="100%"
      height="700px"
      nodes={[]}
      connectors={[]}
      enableCollaborativeEditing={true}
      historyChange={onHistoryChange}
    >
    </DiagramComponent>
  );
};

export default DiagramCollaborativeComponent;

Conflict policy (optimistic concurrency) in React application

To maintain consistency during collaborative editing, each user applies incoming changes using setDiagramUpdates. After applying changes, the React sample synchronizes its userVersion with the serverVersion through the UpdateVersion event. This version-based approach ensures conflicts are resolved without locking, allowing real-time responsiveness while preserving data integrity.

Add the following code in the React sample application:

import React, { useState, useRef, useEffect } from 'react';
import { DiagramComponent } from '@syncfusion/ej2-react-diagrams';
import * as signalR from '@microsoft/signalr';

const DiagramConflictResolution = () => {
  const [userVersion, setUserVersion] = useState<number>(0);
  const diagramRef = useRef<DiagramComponent>(null);
  const connectionRef = useRef<signalR.HubConnection | null>(null);
  const [roomName] = useState('Syncfusion');

  useEffect(() => {
    // Initialize SignalR connection
    const initializeConnection = async () => {
      if (connectionRef.current === null) {
        const connection = new signalR.HubConnectionBuilder()
          .withUrl('<<Your ServiceURL>>', {
            skipNegotiation: true,
            transport: signalR.HttpTransportType.WebSockets
          })
          .withAutomaticReconnect()
          .build();

        // Listen for remote changes with version tracking
        connection.on('ReceiveData', (diagramChanges: string[], serverVersion: number) => {
          applyRemoteDiagramChanges(diagramChanges, serverVersion);
        });

        // Listen for conflict notifications
        connection.on('ShowConflict', () => {
          showConflict();
        });

        // Listen for explicit version updates
        connection.on('UpdateVersion', (serverVersion: number) => {
          updateVersion(serverVersion);
        });

        await connection.start()
          .then(() => {
            console.log('Connected to SignalR Hub');
            connectionRef.current = connection;
          })
          .catch((error: Error) => {
            console.error('Connection failed:', error);
          });
      }
    };

    initializeConnection();

    return () => {
      if (connectionRef.current && connectionRef.current.state === signalR.HubConnectionState.Connected) {
        connectionRef.current.stop();
      }
    };
  }, []);

  const applyRemoteDiagramChanges = (diagramChanges: string[], serverVersion: number) => {
    // Sets diagram updates to current diagram
    if (diagramRef.current && diagramRef.current.setDiagramUpdates) {
      diagramRef.current.setDiagramUpdates(diagramChanges);
    }
    // Update user version to server version after applying changes
    setUserVersion(serverVersion);
  };

  // Capture local changes and send with version and edited IDs
  const onHistoryChange = async (args: any) => {
    if (!diagramRef.current) {
      return;
    }

    const diagramChanges = diagramRef.current.getDiagramUpdates(args);
    if (diagramChanges && diagramChanges.length > 0) {
      const editedElements = getEditedElements(args);
      // Send changes with version and edited element IDs
      if (connectionRef.current && connectionRef.current.state === signalR.HubConnectionState.Connected) {
        connectionRef.current.invoke('BroadcastToOtherUsers', diagramChanges, userVersion, editedElements, roomName)
          .catch((err: Error) => {
            console.error('Send failed:', err);
          });
      }
    }
  };

  const getEditedElements = (args: any): string[] => {
    // Extract and return IDs of affected nodes/connectors from args
    // TODO: implement extraction logic based on historyChange event args
    return [];
  };

  const updateVersion = (serverVersion: number) => {
    setUserVersion(serverVersion);
  };

  const showConflict = () => {
    // Show notification to inform user their update was rejected due to conflict
    const message = "Your changes conflicted with another user's updates and were not applied. Please refresh to see the latest version.";
    alert(message);
  };

  return (
    <div>
      <DiagramComponent
        ref={diagramRef}
        width="100%"
        height="700px"
        enableCollaborativeEditing={true}
        nodes={[]}
        connectors={[]}
        historyChange={onHistoryChange}
      >
      </DiagramComponent>
    </div>
  );
};

export default DiagramConflictResolution;