准备技术：
1.简单的WebService编写；
2.了解Asp.net Ajax 客户端访问WebService
内容：
asp.net ajax框架在去年看过，只是些基本的使用，并没有过多的去研究它的原理。最近在一个项目中要实现客户端访问WebService并返回DataTable类型的数据，当我调用一个返回DataTable的方法时，不能返回成功，在错误的回调函数中告诉我DataTable是一个循环应用类型，不能序列化。当是想过把DataTable替换成其他类型的数据如ArrayList或则Array等,可是有点心不甘，所以查过各个方面的资料，告诉我微软已经提供了一个解决DataTable的JavaScriptConverter的dll文件，当我在web.config中添加了对这个JavascriptConverter引用即可以将DataTable序列化成Json字符串了。
好了，废话不多说了。下面就自己来做个循环应用的实例，并通过自定义JavascriptConverter来解决循环引用的问题。本文只会简单的介绍下服务器端序列化数据类型到Json的过程，不会太深入。
首先先来定义两个类，想了半天最好的实例就是一对夫妻，一个老公只有一个老婆，这是婚姻法规定的，所以老公类型跟老婆类型就可以达到实例中的循环引用。看下两个类型的类试图：
其实两个类里面的内容都很简单,Husband.cs:
using System;using System.Web;using System.Web.Services;using System.Web.Services.Protocols;using System.ComponentModel;public class Husband
{
private string _firstName; public string FirstName
{
get { return _firstName; } set { _firstName = value; }
} private string _lastName; public string LastName { get { return _lastName; } set { _lastName = value; } } private Wife _wife; public Wife Wife { get { return _wife; } set { _wife = value; } }
}using System;using System.Web;using System.Web.Services;using System.Web.Services.Protocols;using System.ComponentModel;public class Wife{ private string _firstName; public string FirstName { get { return _firstName; } set { _firstName = value; } } private string _lastName; public string LastName { get { return _lastName; } set { _lastName = value; } } private Husband _husband; public Husband Husband { get { return _husband; } set { _husband = value; } }}然后我定义了个Webservice类用来提供Client的访问，HusbandService.cs:
using System;using System.Collections;using System.Linq;using System.Web;using System.Web.Services;using System.Web.Services.Protocols;using System.Xml.Linq;using System.Web.Script.Services;/// <summary>/// Husband's Method/// </summary>[WebService(Namespace = "http://tempuri.org/")][WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)][ScriptService]public class HusbandService : System.Web.Services.WebService { public HusbandService () { //Uncomment the following line if using designed components //InitializeComponent(); } [WebMethod] public Husband GetHusband() { Husband hansband = new Husband(); hansband.FirstName = "Henllyee"; hansband.LastName = "Cui"; Wife wife = new Wife(); wife.FirstName = "Throwen"; wife.LastName = "Yang"; hansband.Wife = wife; wife.Husband = hansband; return hansband; } }我在一个asp.net 页面中通过asp.net ajax对GetHusband()的应用的，JavascriptConverter.aspx：
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="JavascriptConverter.aspx.cs" Inherits="_Default" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head runat="server"> <title>JavaScriptConverter Demo</title></head><body> <form id="form1" runat="server"> <div> <asp:ScriptManager ID="scriptManager" runat="server"> <Services> <asp:ServiceReference Path="~/HusbandService.asmx" /> </Services> </asp:ScriptManager> <script language="javascript" type="text/javascript"> function getServiceHasband() { HusbandService.GetHusband(onSuccess,onFailed); } function onSuccess(result) { alert(result.FirstName); } function onFailed(error) { alert(error.get_message()); } window.onload=function() { var btnGet = $get("btnGet"); if(btnGet) { btnGet.onclick=getServiceHasband; } } </script> <input type="button" id="btnGet" value="Get HusBand" /> </div> </form></body></html>我们自定的JavascriptConverter必须继承于JavascriptConverter(JavascriptConverter参考文档)，然后去重写里面的两个方法跟一个属性：
1.Deserialize:如何反序列化一个Jason到这个Converter类型；
2.Serialize：如何序列化支持的对象到一个Jason；
3.SupportedTypes：这个Converter支持的类型。
好了下面我们定义下一个Converter来支持循环引用，现在我们先定义如何将去序列化，HusbandConverter.cs：
using System;using System.Data;using System.Configuration;using System.Linq;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.HtmlControls;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Xml.Linq;using System.Web.Script.Serialization;using System.Collections.Generic;/// <summary>/// Husband's Converter/// </summary>public class HusbandConverter:JavaScriptConverter{ public HusbandConverter() { } /// <summary> /// /// </summary> /// <param name="dictionary"></param> /// <param name="type"></param> /// <param name="serializer"></param> /// <returns></returns> public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer) { throw new NotImplementedException(); } /// <summary> /// Serizlize a json /// </summary> /// <param name="obj"></param> /// <param name="serializer"></param> /// <returns></returns> public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer) { Husband husband = (Husband)obj; IDictionary<string,object> dictionary = new Dictionary<string,object>(); husband.Wife.Husband = null; dictionary["FirstName"] = husband.FirstName; dictionary["LastName"] = husband.LastName; dictionary["Wife"] = husband.Wife; return dictionary; } /// <summary> /// Support Types /// </summary> public override System.Collections.Generic.IEnumerable<Type> SupportedTypes { get { yield return typeof(Husband); } }}然后我们在web.config中注册这样一段对这个Converter的引用:
<system.web.extensions> <scripting> <webServices> <jsonSerialization> <converters> <add name="HusbandConvert" type="HusbandConverter,App_Code"/> </converters> </jsonSerialization> </webServices> </scripting> </system.web.extensions>这下我们再运行时，去点击按钮就能返回“Henllyee”。
在上面中我们首先重写了SupportedTypes属性去告诉系统我这个Converter支持那些类型的数据。然后我们去重写了Serialize方法，其实我们在这里只是把husband.Wife.Husband设置为了null,让它不去循环引用了，所以这样就破坏原来的类的本意。但是我们可以在客户端再去完善它，再在客户端设置husband.Wife.Husband=husband即可了。
下面我们再看如何进行反序列化了。首先我们在webservice中先添加一个方法，来传入Husband对象
[WebMethod] public string GetHusbandInfo(Husband hansband) { Debug.Assert(hansband.Wife.Husband == hansband); return String.Format( "Husband's :{0}\n Wife:{1}", hansband.FirstName + " " + hansband.LastName, hansband.Wife.FirstName + " " + hansband.LastName); }然后我们再去把反序列化实现下：
public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer) { Husband husband = new Husband(); husband.FirstName = (string)dictionary["FirstName"]; husband.LastName = (string)dictionary["LastName"]; husband.Wife = serializer.ConvertToType<Wife>(dictionary["Wife"]); husband.Wife.Husband = husband; return husband; }最后我们在客户端进行调用：
function getHusbandInfo() { var husband = new Object(); husband.FirstName="Henllyee"; husband.LastName="Cui"; var wif = new Object(); wif.FirstName="Erry"; wif.LastName="Du"; husband.Wife=wif; HusbandService.GetHusbandInfo(husband,onGetInfoSucceded,onFailed); } function onGetInfoSucceded(result) { alert(result); }具体的前台的脚本就不在给出，通过运行我们会发现反序列化是成功的。
程序下载地址：https://files.cnblogs.com/henllyee/JavascriptConverter.rar