启动时的ASP.NET SignalR C＃客户端应用程序异常

Question

I have a ASP.NET application. I run it by hitting debug. It runs on localhost:2842.

I have a SignalR Hub defined in a class with no methods on the server.

I have a WPF Windows C# application. I added the SignalR NuGet package. I use the following code to instantiate the client proxy:

        var hubConnection = new HubConnection("http://localhost:2842");

        IHubProxy myHubProxy = hubConnection.CreateHubProxy("MyHub");
        myHubProxy.On<string>("SendMeData", dataString => {

            Console.WriteLine("String value {0}", dataString);
        });

        hubConnection.Start().Wait();

Here is my hub class defined on the server:

public class MyHub : Hub
{
    public static void SendMeData(string dataString)
    {
        var context = GlobalHost.ConnectionManager.GetHubContext<MyHub>();
        if (context != null)
            context.Clients.All.SendMeData(dataString);
    }
}

I have this code in Startup.cs:

public partial class Startup
{
    public void Configuration(IAppBuilder app)
    {
        ConfigureAuth(app);

        app.MapSignalR(new HubConfiguration
        {
            EnableDetailedErrors = true
        });
    }
}

The problem I am having is that when the C# client calls hubConnection.Start().Wait(); I get a very unhelpful exception. Here is the exception:

StatusCode: 500, ReasonPhrase: 'Internal Server Error', Version: 1.1, Content:
System.Net.Http.StreamContent, Headers:  Transfer-Encoding: chunked
X-SourceFiles: =?UTF-8?B?QzpcTXlEZXZcUmVhbHRpbWVNRFxSZWFsdGltZU1EUHJvdG9cUmVhbHRpbWVNRFByb3RvXHNpZ25hbHJcbmVnb3RpYXRl?=
Cache-Control: private  Date: Thu, 27 Apr 2017 04:23:18 GMT  Server: Microsoft-IIS/10.0
X-AspNet-Version: 4.0.30319  X-Powered-By: ASP.NET  Content-Type: text/html; charset=utf-8

I set break points in the server code and it never hits any of them.

How do I figure this out?

Answer 1

In your MyHub class, you've got the following line:

var context = GlobalHost.ConnectionManager.GetHubContext<MyHub>();
        if (context != null)

Get rid of this. Instead your MyHub class should be:

public class MyHub : Hub
{
    public static void SendMeData(string dataString)
    {
       Clients.All.SendMeData(dataString);
    }
}

GetHubContext is used for getting a reference to a Hub from another class within the same AppDomain. For example, if you are in a Controller class and need to call a method on a Hub within the same AppDomain, you would get a reference to the Hub via GetHubContext.

Also in your client code, please remove the .Wait(). The code should be

await hubConnection.Start();

Reference

Answer 2

The whole problem ended up being that I had changed the name of my Hub class in the server without changing the name used in CreateHubProxy. it is working now.

Answer 3

There're probably two reasons for this symptom:

1. The hub name is not found, or misspelled.
2. The hub class is not public.

Anyway, the SignalR library is too bad to not pointing out the real cause, with only a 500 code in error!!