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Home Interviews How can you handle user connection and disconnection events in SignalR? – MindStick
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1 Answers

ICSM Computer
ICSM Computer 22 May 2025
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In SignalR, you can handle user connection and disconnection events by overriding the virtual methods OnConnectedAsync and OnDisconnectedAsync in your Hub class.

Basic Implementation

public class ChatHub : Hub
{
    // Called when a new client connects
    public override async Task OnConnectedAsync()
    {
        string connectionId = Context.ConnectionId;
        string userId = Context.UserIdentifier;

        Console.WriteLine($"User connected. UserId: {userId}, ConnectionId: {connectionId}");

        // Optionally store user-connection mapping
        // Notify others or update UI

        await base.OnConnectedAsync();
    }

    // Called when a client disconnects
    public override async Task OnDisconnectedAsync(Exception exception)
    {
        string connectionId = Context.ConnectionId;
        string userId = Context.UserIdentifier;

        Console.WriteLine($"User disconnected. UserId: {userId}, ConnectionId: {connectionId}");

        // Clean up user-connection mapping
        // Notify others or update UI

        await base.OnDisconnectedAsync(exception);
    }
}

Notes

1. User Identification

  1. Context.ConnectionId: Unique for each connection.
  2. Context.UserIdentifier: Set automatically if authentication is configured.
  3. Context.User: Full ClaimsPrincipal for the user.

To customize UserIdentifier, use a custom IUserIdProvider:

public class CustomUserIdProvider : IUserIdProvider
{
    public string GetUserId(HubConnectionContext connection)
    {
        // Return a custom ID, e.g., username from claims
        return connection.User?.FindFirst("sub")?.Value;
    }
}

Register it:

services.AddSingleton<IUserIdProvider, CustomUserIdProvider>();

2. Common Use Cases

  1. Tracking online/offline status
  2. Managing user groups
  3. Cleaning up resources or subscriptions
  4. Broadcasting status changes (e.g., “User X has joined”)

Example: Notifying Others

public override async Task OnConnectedAsync()
{
    await Clients.Others.SendAsync("UserConnected", Context.UserIdentifier);
    await base.OnConnectedAsync();
}

public override async Task OnDisconnectedAsync(Exception exception)
{
    await Clients.Others.SendAsync("UserDisconnected", Context.UserIdentifier);
    await base.OnDisconnectedAsync(exception);
}
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