A Simple Analogy

Imagine a walkie-talkie for your web app. Instead of sending letters (HTTP requests) and waiting for replies, SignalR lets your app talk instantly—like a live conversation. When something happens, everyone hears about it right away.

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What Is SignalR?

SignalR is a library for ASP.NET Core that enables real-time communication between server and clients. It uses WebSockets (when available) or falls back to other techniques, so updates can be pushed instantly to browsers, mobile apps, or other clients.

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Why Use Real-Time Communication?

• Instant updates: Users see changes as they happen (chat, notifications, dashboards)
• Collaboration: Multiple users can work together in real time (whiteboards, games)
• Live data: Stock prices, sports scores, IoT device status
• Better UX: No need to refresh or poll for changes

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How SignalR Works

• Hub: Central class that manages connections and messaging
• Client: Browser, mobile app, or desktop app that connects to the hub
• Connection: Persistent link (WebSocket, SSE, or long polling)
• Methods: Server can call client methods, and clients can call server methods

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Quick Setup Example

1. Add SignalR NuGet Package

dotnet add package Microsoft.AspNetCore.SignalR

2. Create a Hub

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

3. Configure in Program.cs

builder.Services.AddSignalR();

var app = builder.Build();
app.MapHub<ChatHub>("/chatHub");

4. Client-Side (JavaScript)

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

connection.on("ReceiveMessage", (user, message) => {
    // Update UI with new message
});

await connection.start();
connection.invoke("SendMessage", "Alice", "Hello!");

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Practical Examples

• Live chat rooms
• Real-time notifications (orders, alerts)
• Collaborative editing (documents, whiteboards)
• Live dashboards (metrics, analytics)
• Online games (multiplayer moves, scores)

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Real-World Use Cases

• Customer support chat on websites
• Stock trading platforms with live price updates
• Multiplayer online games
• IoT dashboards showing device status
• Team collaboration tools (Trello, Google Docs-like apps)

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Best Practices

• Use authentication to secure connections
• Scale out with Redis or Azure SignalR Service for many users
• Handle connection drops and reconnections gracefully
• Limit broadcast scope (send to groups/users, not always to all)
• Monitor and log connection events for diagnostics
• Optimize payload size for performance

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Related Concepts to Explore

• WebSockets and HTTP/2
• Server-Sent Events (SSE)
• Pub/Sub messaging patterns
• Event-driven architecture
• Push notifications (mobile/web)
• Group messaging and user targeting
• Scaling real-time apps (Redis, Azure SignalR)
• Blazor Server (real-time UI updates)
• gRPC streaming
• Connection state management

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Summary

SignalR makes real-time communication easy in ASP.NET Core. With just a few lines of code, you can build apps that feel alive—users see updates instantly, collaborate, and interact in ways that aren't possible with traditional request/response web apps.