WCF JSON returns XML data!

I'm building a WCF REST Web service which should output JSON, but I'm getting XML.

I'm using ResponseFormat = WebMessageFormat.Json

Please help I search everywhere and I couldn't find the solution.

Note: I even tried the suggestion from here

config file

<services> 
  <service name="TestService"> 
     <endpoint address="" 
               behaviorConfiguration="Tes开发者_开发问答tServiceAspNetAjaxBehavior" 
               binding="webHttpBinding" 
               bindingConfiguration="webBinding" 
               contract="TestService" /> 
   </service> 
 </services> 
 <bindings> 
     <webHttpBinding> 
         <binding name="webBinding"> 
              <security mode="Transport"> 
              </security> 
          </binding> 
      </webHttpBinding> 
 </bindings>

Some things you need to check:

• The "name" attribute of your <service> element in web.config needs to match the fully-qualified name of the service class - if TestService is on namespace MyNamespace, then the service must be declared as <service name="MyNamespace.TestService"> - in other words, it must match the name you have in the '.svc' file for your service
• Your endpoint declaration doesn't specify a behaviorConfiguration attribute; for WCF web endpoints, you need both to have the webHttpBinding and the a reference to a behavior which declares (in your case) <webHttp />
• Another option is to use the WebServiceHostFactory in the .svc file: <% @ServiceHost Service="MyNamespace.TestService" Factory="System.ServiceModel.Activation.WebServiceHostFactory" Language="C#" debug="true" %>. With this you don't need to have the service defined in config.

I had a similar issue because I had a tag like this;

<behavior name="jsonBehavior">
          <enableWebScript/>
          <webHttp helpEnabled="true"/>
        </behavior>

after I remove

<webHttp helpEnabled="true"/>

it is fixed. Maybe it is a bug. I am not sure.