Introduction

Yesterday I wrote a blog about SignalR and just 5 seconds after posting it I got this on twitter.

So, here I am on a Sunday morning writing about SignalR and Hubs.

Why hubs? You ask.

Hubs provide a higher level RPC framework over a PersistentConnection. If you have different types of messages that you want to send between server and client then hubs is recommended so you don't have to do your own dispatching.

It took me a while to figure this out, but I got there in the end.

The server

Setting up the server should have been easy. But it lacked something.

So watch out if you are working with VB.Net.

First I started to create my hub.

This hub should return a plant for the id given or nothing when the id is not found.

If you start this you should get the url to your server.

if you browse to that url and add /signalr/hubs to it you should get something like this.

/*!
* ASP.NET SignalR JavaScript Library v1.0.0
* http://signalr.net/
*
* Copyright Microsoft Open Technologies, Inc. All rights reserved.
* Licensed under the Apache 2.0
* https://github.com/SignalR/SignalR/blob/master/LICENSE.md
*
*/

/// /// (function ($, window) { /// "u

But I did not get that. I got a 404 not found page instead. Which isn't good.

And it was caused by the routes not being registered. Which normally happens via this cs file that is in your App_Start folder (which was created by the nuget package).

.Web.Routing;
using Microsoft.AspNet.SignalR;
using Microsoft.AspNet.SignalR.Hosting.AspNet;

[assembly: PreApplicationStartMethod(typeof(SignalRTesting.RegisterHubs), "Start")]

namespace SignalRTesting
{
    public static class RegisterHubs
    {
        public static void Start()
        {
            // Register the default hubs route: ~/signalr/hubs
            RouteTable.Routes.MapHubs();            
        }
    }
}

And normally you don't need to setup any roots in your Global.asax.

But when I did. It worked.

So add a Global.asax and change it to this.

And now your server should return the correct page on browsing to /signalr/hubs

The client

First thing to try is to make a console client.

Look at the code of our server and see that we return an object of type Plant.

Our Plant object looks like this BTW.

The return means that only the caller will get that returnvalue, not any of the other clients.

And here is such a client.

And if you type 1 you should get this in return.

But we could have just use ServiceStack if we needed something like that.

So what is the point?

Let's just say that we want to inform all our clients that someone just requested a plant with id 1 than we could do this instead.

Change the server code and start it up.

As you can see I use Clients.All.addMessage to send a message to all Clients with the id that was requested.

Change the console client to this.

I just added the plants.On method to intercept the addMessage events.

And now when I open multiple clients I get this.

Which is cool.

Conclusion

Hubs are what you will mostly use when you use SignalR.