using System;
using System.Collections;
using System.Web;
using System.Web.Script.Serialization;

namespace Lab.Web
{
    public class Handler1 : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {

            var data = new Hashtable();
            data["success"] = true;
            data["now"] = DateTime.Now;
            data["message"] = "En Taro Adun!";

            var jss = new JavaScriptSerializer();
            var json = jss.Serialize(data);

            context.Response.ContentType = "text/javascript";
            context.Response.Write(json);
        }

        public bool IsReusable
        {
            get { return false; }
        }
    }
}

------解决方案--------------------
//返回集合跟返回对象是一样的处理模式

前端交互
	$.ajax({
			type: "get",
			url: "@Url.Action("ShowDetail","UserInfo")",
			data: "ID="+id,
			dataType:"json",
			success: function (msg) { //msg是一个对象  如果是集合的话就要msg[i].UserName 来获取UserName这个属性的值
			   		$("#DUserName").val(msg.UserName);
					$("#Dpwd").val(msg.pwd);
					$("#Daddress").val(msg.address);
			},
			error:function(XMLHttpRequest, textStatus, errorThrown){
			alert(errorThrown);
			}
		});
//后台处理
	public JsonResult ShowDetail() {
			var id = Convert.ToInt32(Request["id"].ToString());
			UserInfo u = db.UserInfo.Single(ui=>ui.id== id); //根据id查询单个对象
  U里面有UserName pwd address  等属性  
		  	return Json(u,JsonRequestBehavior.AllowGet);
//这里是返回单个对象 返回list也类似  
			
		  }