SignalR HTTP 500 when calling server method from client

Question

I'm just getting started with SignalR and have been able to broadcast messages out to all connected clients without any problems. I'd now like to have my client (javascript) join a group and receive only messages for that group. In my hub, I have the following method that adds connections to named groups:

    public Task JoinGroup(string groupName)
    {
        return this.Groups.Add(Context.ConnectionId, groupName);
    }

On the client, I have the following JS:

        var latLonBounds = new google.maps.LatLngBounds();
        var tripIdentifier = '@Model.TripIdentifier';
        $(function () {
            var hub = $.connection.locationHub;
            hub.client.updateLocation = function (coordinates) {
                  // Implementation omitted
                });

                latLonBounds.extend(position);
                map.fitBounds(latLonBounds);
            };
            $.connection.hub.logging = true;
            $.connection.hub.start().done(function() {
                hub.server.joinGroup(tripIdentifier);
            });
        });

When my page loads,in Chrome, I see an HTTP 500 for the following URL in the console:

http://localhost:49914/signalr/send?transport=serverSentEvents&connectionToken=AQAAANCMnd8BFdERjHoAwE%2FCl%2BsBAAAA8OmZGDrRfEaOjaHahkkarwAAAAACAAAAAAAQZgAAAAEAACAAAADM78kCBInmZa7OROdPoXraiugBXLR5Xu3htxYC2JSnSAAAAAAOgAAAAAIAACAAAAAZwnPx6GMKOiw%2FivqQPlSfCb4WNP342YxvGyBpalmjSDAAAADljl1vg%2F7GYtD3R4AA2A9LXEnNZkyQVQjDUrW7ZVbvfPpWz1GCcOn6aw5yrkrWFrhAAAAAyX5otz0Xhx8tuIRgX2Pr1b9ZWFMvoairvqzns1%2FhjN%2BRhDIuAqAfonTbsZDjkdyDAZXzAKQqwTEKhpa5LYBhKg%3D%3D

In Visual Studio, I see the following stack trace:

SignalR exception thrown by Task: System.AggregateException: One or more errors occurred. ---> System.MissingMethodException: No parameterless constructor defined for this object.
   at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
   at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
   at System.Activator.CreateInstance(Type type, Boolean nonPublic)
   at System.Activator.CreateInstance(Type type)
   at Microsoft.AspNet.SignalR.Hubs.DefaultHubActivator.Create(HubDescriptor descriptor)
   at Microsoft.AspNet.SignalR.Hubs.DefaultHubManager.ResolveHub(String hubName)
   at Microsoft.AspNet.SignalR.Hubs.HubDispatcher.CreateHub(IRequest request, HubDescriptor descriptor, String connectionId, StateChangeTracker tracker, Boolean throwIfFailedToCreate)
   at Microsoft.AspNet.SignalR.Hubs.HubDispatcher.OnReceived(IRequest request, String connectionId, String data)
   at Microsoft.AspNet.SignalR.PersistentConnection.<>c__DisplayClassa.<>c__DisplayClassc.<ProcessRequest>b__7()
   at Microsoft.AspNet.SignalR.TaskAsyncHelper.FromMethod(Func`1 func)
   --- End of inner exception stack trace ---
---> (Inner Exception #0) System.MissingMethodException: No parameterless constructor defined for this object.
   at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
   at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
   at System.Activator.CreateInstance(Type type, Boolean nonPublic)
   at System.Activator.CreateInstance(Type type)
   at Microsoft.AspNet.SignalR.Hubs.DefaultHubActivator.Create(HubDescriptor descriptor)
   at Microsoft.AspNet.SignalR.Hubs.DefaultHubManager.ResolveHub(String hubName)
   at Microsoft.AspNet.SignalR.Hubs.HubDispatcher.CreateHub(IRequest request, HubDescriptor descriptor, String connectionId, StateChangeTracker tracker, Boolean throwIfFailedToCreate)
   at Microsoft.AspNet.SignalR.Hubs.HubDispatcher.OnReceived(IRequest request, String connectionId, String data)
   at Microsoft.AspNet.SignalR.PersistentConnection.<>c__DisplayClassa.<>c__DisplayClassc.<ProcessRequest>b__7()
   at Microsoft.AspNet.SignalR.TaskAsyncHelper.FromMethod(Func`1 func)<---

If I remove the call to hub.server.joinGroup(tripIdentifier); from my JS, then I don't get the HTTP 500/exception so it seems like this line is the source of the exception.

Any suggestions as to what I can do to get group registration working would be much appreciated.

Thanks!

Answer 1

This is the part of the stack that tells you what's wrong:

---> (Inner Exception #0) System.MissingMethodException: No parameterless constructor defined    for this object.
   at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)
   at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)
   at System.Activator.CreateInstance(Type type, Boolean nonPublic)
   at System.Activator.CreateInstance(Type type)
   at Microsoft.AspNet.SignalR.Hubs.DefaultHubActivator.Create(HubDescriptor descriptor

Basically what's that's saying is your hub class doesn't have a parameterless constructor. If you're trying to setup dependency injection for your hubs you appear to have an issue with registering your dependency resolver with SignalR. If you provide more details we can probably help you with getting that fixed as well.