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问题:

I'm getting this error when attempting to load classes in the Microsoft.AspNet.SignalR.Owin assembly.

The exception is thrown after execution leaves the Configurationmethod in startup.cs. I've registered a Global Exception Handler to try and catch the exception but it is not being caught.

public async override Task HandleAsync(ExceptionHandlerContext context, CancellationToken cancellationToken)
        {

            var exception = context.Exception;

            const string genericErrorMessage =  "An unexpected error occured";
            var response = context.Request.CreateResponse(HttpStatusCode.InternalServerError,
                new
                {
                    Message = genericErrorMessage
                });

            response.Headers.Add("X - Error & ", genericErrorMessage);
            context.Result = new ResponseMessageResult(response);
        }

config.Services.Replace(typeof(IExceptionHandler), new GlobalExceptionHandler());

the Application_Error method in Global.asax doesn't catch it either

 protected void Application_Error(object sender, EventArgs e)
    {
        HttpContext ctx = HttpContext.Current;
        KeyValuePair<string, object> error = new KeyValuePair<string, object>("ErrorMessage", ctx.Server.GetLastError().ToString());
        ctx.Response.Clear();
    }

I've tried reinstalling the assembly but to no avail.

There's two other questions on SO but no solutions

Despite configuring Visual studio to break on every possible type of exception, this is still not being caught. The only place i can tell an exception has occurred is in the output window. Nothing is logged to the event logs.

For info this is using VS 2015

SignalR.ReflectedHubDescriptorProvider Warning: 0 : Some of the classes from assembly "Microsoft.AspNet.SignalR.Owin, Version=1.2.2.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" could Not be loaded when searching for Hubs. [...\Microsoft.AspNet.SignalR.Owin.dll]

Original exception type: ReflectionTypeLoadException

Original exception message: Unable to load one or more of the requested types. Retrieve the LoaderExceptions property for more information.

EDIT: I'm running all the latest Signalr packages

Installed signalr related packages

Autofac.SignalR v 3.0.2

Microsoft.AspNet.SignalR v2.2.0

Microsoft.AspNet.SignalR.Core v2.2.0

Microsoft.AspNet.SignalR.JS v2.2.0

Microsoft.AspNet.SignalR.Owin v1.2.2

Microsoft.AspNet.SignalR.SelfHost v2.2.0

Microsoft.AspNet.SignalR.SystemWeb v2.2.0

回答1:

What you are seeing is a log entry create by: ReflectedHubDescriptorProvider

102 try 
103             { 
104                 return a.GetTypes(); 
105             } 
106             catch (ReflectionTypeLoadException ex) 
107             { 
108                 _trace.TraceWarning("Some of the classes from assembly \"{0}\" could Not be loaded when searching for Hubs. [{1}]\r\n" + 
109                                     "Original exception type: {2}\r\n" + 
110                                     "Original exception message: {3}\r\n", 
111                                     a.FullName, 
112                                     a.Location, 
113                                     ex.GetType().Name, 
114                                     ex.Message); 


116                 return ex.Types.Where(t => t != null); 
117             }

The exception can be caused by a missing dependency in one of the loaded assemblies, the signalr code is iterating all your assemblies. So the cause can be in any of currently loaded assembles. Interesting :get-all-types-in-an-assembly and how-to-prevent-reflectiontypeloadexception-when-calling-assembly-gettypes explains the try catch construction used in the ReflectedHubDescriptorProvider. It is just ignoring the classes/hubs it can't load from the Microsoft.AspNet.SignalR.Owin assembly.

The ReflectionTypeLoadException contains a LoaderExceptions, to access it you can download the source code and add tracing on the ex.LoaderExceptions or add a breakpoint in the sourcecode.

回答2:

I 'fixed' this problem by creating a new project and copying everything over to the new one/ reinstalling packages again.

I no longer get this error, but my Signalr problems have not gone away, so it looks like this one was a red herring.

回答3:

Glad to hear that you managed to fix assembly loading issue. Here are some tips that might help you get it running!

Enable logging

To troubleshoot SignalR problems the best thing to do is to enable server & client side logging.

Client side:

$.connection.hub.logging = true;
$.connection.hub.start();

Server side:

var hubConnection = new HubConnection("http://www.contoso.com/");
hubConnection.TraceLevel = TraceLevels.All;
hubConnection.TraceWriter = Console.Out;
IHubProxy stockTickerHubProxy = hubConnection.CreateHubProxy("StockTickerHub");
stockTickerHubProxy.On<Stock>("UpdateStockPrice", stock => Console.WriteLine("Stock update for {0} new price {1}", stock.Symbol, stock.Price));
await hubConnection.Start();

Here are full instructions:

http://www.asp.net/signalr/overview/testing-and-debugging/enabling-signalr-tracing

Check your code and troubleshoot the problem

Here is a list of common mistakes you should check:

Misspelled method, incorrect method signature, or incorrect hub name;
Duplicate method name on client;
Mixing Hub and PersistentConnection syntax;
Connection started before subscriptions are added;
Missing method name on the hub proxy;
Hub or hub methods not declared as Public;
Manually serializing data;
Connection limit reached;
Cross-domain connection not set up properly;

Here is a full article on how to troubleshoot SignalR issues with code samples: http://www.asp.net/signalr/overview/testing-and-debugging/troubleshooting