What is "OnConnected" in SignalR?

In SignalR, OnConnected (or more specifically OnConnectedAsync in modern ASP.NET Core SignalR) is a hub lifecycle method that runs when a client successfully establishes a connection to a hub.

ASP.NET Core SignalR

You typically override OnConnectedAsync in your Hub class:

using Microsoft.AspNetCore.SignalR;

public class ChatHub : Hub
{
    public override async Task OnConnectedAsync()
    {
        string connectionId = Context.ConnectionId;

        Console.WriteLine($"Client connected: {connectionId}");

        await base.OnConnectedAsync();
    }
}

When it is called

The method executes when:

• A client starts a SignalR connection.
• The SignalR handshake completes successfully.
• The connection is registered by the hub.

Common uses

• Logging connection activity
• Tracking online users
• Adding users to groups
• Initializing connection-specific data
• Sending a welcome message

Example:

public override async Task OnConnectedAsync()
{
    await Clients.Caller.SendAsync(
        "ReceiveMessage",
        "Welcome to the chat!");

    await base.OnConnectedAsync();
}

Related lifecycle methods

• OnConnectedAsync() – called when a client connects.
• OnDisconnectedAsync(Exception? exception) – called when a client disconnects.
• Hub methods (your custom methods) – called when clients invoke server-side actions.

Older SignalR versions

In classic ASP.NET SignalR (pre-Core), the method was named:

public override Task OnConnected()
{
    return base.OnConnected();
}

In ASP.NET Core SignalR, it was renamed to:

public override Task OnConnectedAsync()
{
    return base.OnConnectedAsync();
}

So if you're working with modern SignalR, OnConnectedAsync() is the method you'll use to execute logic whenever a new client connection is established.