What is SignalR in Dot Net Core MVC

SignalR is a real-time communication library from Microsoft that lets a server instantly push updates to connected clients (like web browsers, mobile apps, or desktop apps).

In simple terms

Instead of a client repeatedly asking the server, “Anything new?”, SignalR allows the server to say, “Hey, here’s new data right now!” — instantly.

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What it’s used for

SignalR is commonly used in apps that need live updates, such as:

• Chat applications (like messaging apps)
• Live dashboards (stocks, analytics)
• Online gaming
• Notifications (alerts, updates)
• Collaborative tools (shared editing)

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How it works (conceptually)

SignalR manages the connection between client and server using the best available method:

• WebSockets (fastest, if supported)
• Server-Sent Events
• Long polling (fallback)

You don’t have to worry about which one—it handles that automatically.

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Example scenario

Imagine a chat app:

• User A sends a message
• The server receives it
• SignalR immediately pushes that message to User B (no refresh needed)

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Where it fits

SignalR is part of the ASP.NET ecosystem and works especially well with .NET applications, though clients can be written in JavaScript, C#, and more.

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Key benefits

• Real-time communication
• Handles connection management for you
• Scales with cloud services
• Works across platforms

 1. Install SignalR

SignalR is already included in modern ASP.NET Core, but if needed:

dotnet add package Microsoft.AspNetCore.SignalR

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⚡ 2. Create a Hub (Server-side)

A Hub is the core class that handles communication.

using Microsoft.AspNetCore.SignalR;

public class ChatHub : Hub
{
    public async Task SendMessage(string user, string message)
    {
        // Send message to all connected clients
        await Clients.All.SendAsync("ReceiveMessage", user, message);
    }
}

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⚙️ 3. Configure in Program.cs

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSignalR();

var app = builder.Build();

app.MapHub<ChatHub>("/chatHub");

app.Run();

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🌐 4. Client-side (JavaScript)

<script src="https://cdnjs.cloudflare.com/ajax/libs/microsoft-signalr/7.0.5/signalr.min.js"></script>

<script>
    const connection = new signalR.HubConnectionBuilder()
        .withUrl("/chatHub")
        .build();

    // Receive message from server
    connection.on("ReceiveMessage", (user, message) => {
        console.log(user + ": " + message);
    });

    // Start connection
    connection.start().then(() => {
        console.log("Connected");

        // Send message to server
        connection.invoke("SendMessage", "Shiva", "Hello SignalR!");
    });
</script>

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🔁 How this works

1. Client connects to /chatHub
2. Client calls SendMessage
3. Server (Hub) receives it
4. Server broadcasts via ReceiveMessage
5. All clients instantly get the message

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🎯 Output

Shiva: Hello SignalR!