How to get JSON response from a 3.5 asmx web service

Question

I have the following method:

using System.Web.Services;
using System.Web.Script.Services;
using System.Web.Script.Serialization;
using Newtonsoft.Json;
using         


        

Answer 1

Dear future readers: The currently accepted answer is not the right way. It ties you to using the JavaScriptSerializer and you lose the ability to request xml (or indeed any serialization format which may come along in the future). The "right way" also involves less code!

If you decorate your service class with the [ScriptService] attribute - which you have - then ASP.NET 3.5+ should automatically serialise the response to JSON provided your Ajax call requests JSON. The suggestions to serialise to JSON manually are simply wrong, unless you wish to use a different serialiser such as Newtonsoft.

That you were seeing XML suggests one of the following:

• You are not requesting JSON in your Ajax call - please see working example code below
• Possibly some web.config entries are missing, according to an answer here (disclaimer: I don't have most of these in a production web.config; only start playing with these if nothing else works)

Here is a simple working example of a JSON enabled ASMX web service:

<%@ WebService Language="C#" Class="WebService" %>
using System;
using System.Collections.Generic;
using System.Web.Services;

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.Web.Script.Services.ScriptService]
public class WebService : System.Web.Services.WebService {
    [WebMethod]
    public MyClass Example()
    {
        return new MyClass();
    }

    public class MyClass
    {
        public string Message { get { return "Hi"; } }
        public int Number { get { return 123; } }
        public List List { get { return new List { "Item1", "Item2", "Item3" }; } }
    }
}

JavaScript to request it and process the response (we'll simply pop up a JS alert with the message from MyClass.Message) :

Http request:

POST http://HOST.com/WebService.asmx/Example HTTP/1.1
Accept: application/json, text/javascript, */*; q=0.01
Content-Type: application/json; charset=utf-8
X-Requested-With: XMLHttpRequest
Referer: http://HOST.com/Test.aspx
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; WOW64; Trident/6.0)
Connection: Keep-Alive
Content-Length: 3
Host: HOST.com

{ }

HTTP response:

HTTP/1.1 200 OK
Cache-Control: private, max-age=0
Content-Type: application/json; charset=utf-8
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Tue, 20 Feb 2018 08:36:12 GMT
Content-Length: 98

{"d":{"__type":"WebService+MyClass","Message":"Hi","Number":123,"List":["Item1","Item2","Item3"]}}

Result:

"Hi" is displayed in a JS popup.