WCF method called twice

问题

I have a web service which is returning data to the desktop application. The problem I am having is, when the web service returns small volume of data everything works fine but when the volume of data is large it throws the following exception:

System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a receive.

And when I am debugging the web service, I see that this particular method is called twice. It executes the return statement 1st time nothing happens, but when it does execute it for the second time the above mentioned exception is thrown in the desktop app.

I found similar posts before on stackoverflow but they did not solve my problem. Can anybody please tell me what's going on in here?

Thanks!

回答1:

It could be because the size of the message is greater than the default message size. You might try increasing the this value in the configuration of the endpoint. You could also take a look at this post.

UPDATE:

To further diagnose the problem I would suggest you activating the trace on the service by putting the following in the config file:

<system.diagnostics>
    <trace autoflush="true">
    </trace>
    <sources>
        <source name="System.ServiceModel"
                switchValue="Information, ActivityTracing"
                propagateActivity="true">
            <listeners>
                <add name="sdt"
                     type="System.Diagnostics.XmlWriterTraceListener"
                     initializeData="WcfDetailTrace.e2e" />
            </listeners>
        </source>
    </sources>
</system.diagnostics>

This will generate the WcfDetailTrace.e2e trace file which you could open with the Service Trace Viewer Tool which will provide you with extensive information about the call and the error message.

回答2:

I recently had this issue.

It turned out that analyzing the WCF log as written by the System.Diagnostics.XmlWriterTraceListener yielded a problem with the data contract I had set up.

I am returning Dictionary<int, object> (Side Note: Yes, I know this is really bad!, but I am young and need the money). I forgot to include the [KnownType] attribute on the return value for the DataContract:

    [DataContract]
    [KnownType(typeof(Dictionary<int, double>))]
    [KnownType(typeof(Dictionary<int, ChannelData>))]
    [KnownType(typeof(Dictionary<string, Dictionary<int, double>>))]
    public class MyCoolObject: ICoolObject
    {
[DataMember]
        public Dictionary<string, object> Results
        {
            get { return _results; }
            set { _results = value; }
        }
    }

回答3:

I too had this issue. For me, it was happening because I had a [DataMember] property with a get{} but no set{}. After adding a set{} this behavior stopped.

回答4:

I encountered this same problem. It turned out WCF couldn't return DateTime as JSON, so I had to make it Nullable<DateTime>.

回答5:

I recently had this problem, and it turned out i have forgotten to mark one of the data transfer classes with [DataContract]

回答6:

I also had this problem and my solution was similar to Batgar's, but with a twist. I had a class that had a property of type object. I had to add KnownType attributes to the class for every type the object could hold. I couldn't populate the KnownType on-the-fly as the class didn't know what the object will contain.

回答7:

I ran into the exact same symptoms as OP, but my target was an Oracle webservice that I have no control over. WebService calls worked fine from a standalone test web-application, but not from the .NET app that required the implementation.

I don't understand why, but updating the targetFramework in web.config from 4.5 to 4.6.1 fixed the issue for my application.

<httpRuntime targetFramework="4.5" requestValidationMode="4.5" executionTimeout="36000" />

<httpRuntime targetFramework="4.6.1" requestValidationMode="4.5" executionTimeout="36000" />

来源：https://stackoverflow.com/questions/2669100/wcf-method-called-twice

标签

wcf

web-services

system.net.webexception