asp.net asmx web service returning xml instead of json

Finally figured it out.

The app code is correct as posted. The problem is with the configuration. The correct web.config is:

<configuration>    <system.web>        <compilation debug="true" targetFramework="4.0" />    </system.web>    <system.webServer>        <handlers>            <add name="ScriptHandlerFactory"                 verb="*" path="*.asmx"                 type="System.Web.Script.Services.ScriptHandlerFactory, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"                 resourceType="Unspecified" />        </handlers>    </system.webServer></configuration>

According to the docs, registering the handler should be unnecessary from .NET 4 upwards as it has been moved to the machine.config. For whatever reason, this isn't working for me. But adding the registration to the web.config for my app resolved the problem.

A lot of the articles on this problem instruct to add the handler to the <system.web> section. This does NOT work and causes a whole load of other problems. I tried adding the handler to both sections and this generates a set of other migration errors which completely misdirected my troubleshooting.

In case it helps anyone else, if I had ther same problem again, here is the checklist I would review:

1. Did you specify type: "POST" in the ajax request?
2. Did you specify contentType: "application/json; charset=utf-8" in the ajax request?
3. Did you specify dataType: "json"in the ajax request?
4. Does your .asmx web service include the [ScriptService] attribute?
5. Does your web method include the [ScriptMethod(ResponseFormat = ResponseFormat.Json)] attribute? (My code works even without this attribute, but a lot of articles say that it is required)
6. Have you added the ScriptHandlerFactory to the web.config file in <system.webServer><handlers>?
7. Have you removed all handlers from the the web.config file in in <system.web><httpHandlers>?

Hope this helps anyone with the same problem. and thanks to posters for suggestions.

No success with above solution, here how I resolved it.

put this line into your webservice and rather return type just write the string in response context

this.Context.Response.ContentType = "application/json; charset=utf-8";this.Context.Response.Write(serial.Serialize(city));

If you want to stay remain with Framework 3.5, you need to make change in code as follows.

[WebService(Namespace = "http://tempuri.org/")][WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. [ScriptService]public class WebService : System.Web.Services.WebService{    public WebService()    {    }    [WebMethod]    public void HelloWorld() // It's IMP to keep return type void.    {        string strResult = "Hello World";        object objResultD = new { d = strResult }; // To make result similarly like ASP.Net Web Service in JSON form. You can skip if it's not needed in this form.        System.Web.Script.Serialization.JavaScriptSerializer ser = new System.Web.Script.Serialization.JavaScriptSerializer();        string strResponse = ser.Serialize(objResultD);        string strCallback = Context.Request.QueryString["callback"]; // Get callback method name. e.g. jQuery17019982320107502116_1378635607531        strResponse = strCallback + "(" + strResponse + ")"; // e.g. jQuery17019982320107502116_1378635607531(....)        Context.Response.Clear();        Context.Response.ContentType = "application/json";        Context.Response.AddHeader("content-length", strResponse.Length.ToString());        Context.Response.Flush();        Context.Response.Write(strResponse);    }}