SignalR Real-Time Communication in ASP.NET Core
💡 Concept Name
SignalR in ASP.NET Core
📘 Quick Intro
SignalR is a library in ASP.NET Core that enables real-time communication between server and client over WebSockets, Server-Sent Events, or Long Polling—allowing instant updates to the UI without refreshing.
🧠 Analogy / Short Story
Think of SignalR as a walkie-talkie between your server and browser. Instead of shouting and hoping the browser hears it later (traditional polling), SignalR keeps the channel open so messages are sent and heard immediately.
🔧 Technical Explanation
SignalR abstracts transport protocols and allows bi-directional communication using WebSockets where possible, and gracefully falls back to SSE or long polling. It enables real-time push-style updates such as notifications, live chat, or dashboards.
It supports scale-out via Redis backplanes and integrates well with Blazor, React, or plain JS clients.
🎯 Purpose & Use Case
- ✅ Live chat applications
- ✅ Real-time dashboards and analytics
- ✅ Notifications (stock price, orders, social updates)
- ✅ Collaborative apps (whiteboards, docs)
- ✅ Multiplayer gaming and live polling
💻 Real Code Example
SignalR Chat Example:
// ChatHub.cs
public class ChatHub : Hub
{
public async Task SendMessage(string user, string message)
{
await Clients.All.SendAsync("ReceiveMessage", user, message);
}
}
// Program.cs
builder.Services.AddSignalR();
app.MapHub<ChatHub>("/chathub");
// client.js
const connection = new signalR.HubConnectionBuilder()
.withUrl("/chathub").build();
connection.on("ReceiveMessage", (user, message) => {
console.log(`${user}: ${message}`);
});
connection.start().then(() => {
connection.invoke("SendMessage", "Alice", "Hello!");
});
Highlight: One hub, multiple clients, real-time communication enabled with minimal setup.
❓ Interview Q&A
Q1: What is SignalR?
A: A real-time communication library for ASP.NET Core that enables server-to-client push functionality.
Q2: How does SignalR select transport?
A: It auto-negotiates the best transport: WebSockets, Server-Sent Events, or Long Polling.
Q3: What is a Hub in SignalR?
A: A central class through which clients and server communicate in SignalR.
Q4: How does a client subscribe to a SignalR hub?
A: By using the `HubConnectionBuilder` and attaching listeners for specific methods.
Q5: Is SignalR supported in Blazor?
A: Yes, especially in Blazor Server apps.
Q6: How do you scale SignalR with multiple servers?
A: Using a backplane like Redis.
Q7: Does SignalR support authentication?
A: Yes, it can use cookie or bearer-based authentication.
Q8: Can SignalR push to specific users?
A: Yes, via connection IDs, user identifiers, or groups.
Q9: Is SignalR part of .NET Core SDK?
A: It is part of ASP.NET Core and needs `Microsoft.AspNetCore.SignalR` NuGet package.
Q10: Can I use SignalR without JavaScript?
A: Yes, with .NET, Java, or Python clients.
📝 MCQs
Q1: What transport does SignalR prefer?
- A. Long Polling
- B. WebSockets
- C. FTP
- D. SignalPipe
Q2: Which namespace is needed for SignalR hubs?
- A. Microsoft.Realtime
- B. Microsoft.AspNetCore.SignalR
- C. System.Hub
- D. SignalR.IO
Q3: What is used to start a SignalR connection?
- A. signalR.begin()
- B. connection.start()
- C. hub.connect()
- D. start.signal()
Q4: Which method is used to call a server method from client?
- A. emit()
- B. invoke()
- C. call()
- D. send()
Q5: How do you send message to all clients in a hub?
- A. Clients.Send()
- B. Clients.All.SendAsync()
- C. Broadcast()
- D. Clients.BroadcastAsync()
Q6: What is the fallback for WebSockets in SignalR?
- A. AJAX
- B. Server-Sent Events
- C. GraphQL
- D. SignalHTTP
Q7: Can you create SignalR clients in Python?
- A. No
- B. Yes
- C. Only JS
- D. Only .NET
Q8: Which is not a SignalR feature?
- A. Real-time updates
- B. SQL replication
- C. Group messaging
- D. Automatic reconnection
Q9: What class do hubs derive from?
- A. WebHub
- B. Hub
- C. BaseHub
- D. SignalController
Q10: How does SignalR scale out in multiple servers?
- A. WebFarm
- B. Redis backplane
- C. Round robin
- D. LoadHub
💡 Bonus Insight
SignalR integrates directly with Azure SignalR Service, letting you scale to millions of concurrent connections with simplified connection management and traffic handling.
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