Question

I am trying to make my WCF service method to return JSON-object, but it doesn’t work, when I open in a web browser it shows xml.

How can I make this method return JSON?

I have inserted [WebGet(ResponseFormat = WebMessageFormat.Json)], but that didn’t help

[WebGet(ResponseFormat = WebMessageFormat.Json)]  
protected override IEnumerable<KeyValuePair<string, SampleItem>> OnGetItems()  
{  
   // TODO: Change the sample implementation here  
   if (items.Count == 0)  
   {  
      items.Add("A", new SampleItem() { Value = "A" });  
      items.Add("B", new SampleItem() { Value = "B" });  
      items.Add("C", new SampleItem() { Value = "C" });  
   }  
   return this.items;  
}  

Answer 1

In order for this to work, you need to host this with the webHttpBinding and the WebServiceHostFactory in your web.config and service’s *.svc file.

You didn’t show any web.config or other config – so I cannot really tell what you’re doing. But the JSON response format in the WebGet attribute is only supported in the REST-style WCF services. The WebGet attribute is ignored for any of the SOAP-based bindings, e.g. basicHttpBinding, wsHttpBinding, netTcpBinding and so on.

For more information on REST-style WCF Services, check out the WCF REST Developer Center and read up on how to set up and use REST-style WCF services.

Update: in order for your *.svc file to properly work as a REST service that uses the WebGet attribute and returns JSON, you need to make sure to specify the correct service host factory:

<%@ServiceHost Language="C#" Service="YourService"
               Factory="System.ServiceModel.Activation.WebServiceHostFactory" %>

By specifying the WebServiceHostFactory, you’re telling the WCF runtime to use this service as a REST service, and then all the other pieces should automatically fall into place.