请教一个关于属性的问题

[Dcboy]

有一个类

using System;
using System.Xml.Serialization;
using System.Collections.Generic;
using System.Text;
using GMI.Lib;
using Newtonsoft.Json;

namespace GMI.Model
{
    public class CaseVO
    {
        public int ID = 0;
        public string CaseNo = string.Empty;

        private string m_ExtendXml = string.Empty;
        [JsonIgnore]
        public string ExtendXml
        {
            get
            {
                m_ExtendXml = SerializationHelper.SerializeToXml(m_Extend);
                return m_ExtendXml;
            }
            set { 
                m_ExtendXml = value;
                m_Extend = (CaseExtendVO)SerializationHelper.DeserializeFromXml(m_ExtendXml, typeof(CaseExtendVO));
            }
        }
        private CaseExtendVO m_Extend = new CaseExtendVO();

        public CaseExtendVO Extend
        {
            get
            {
                m_Extend = (CaseExtendVO)SerializationHelper.DeserializeFromXml(m_ExtendXml, typeof(CaseExtendVO));
                return m_Extend;
            }
            set
            {
                m_Extend = value;
                m_ExtendXml = SerializationHelper.SerializeToXml(value);
            }
        }
    }

    public class CaseExtendVO
    {
        /// <summary>
        /// 对于SalesForce的ID 唯一
        /// </summary>
        public string SForceID = string.Empty;

        /// <summary>
        /// 创建时间
        /// </summary>
        [XmlIgnore]
        public DateTime CreateTime = DateTime.Now;

        [XmlElement("CreateTime")]
        [JsonIgnore]
        public string XCreateTime
        {
            get { return this.CreateTime.ToString("yyyy-MM-dd HH:mm:ss"); }
            set { this.CreateTime = DateTime.Parse(value); }
        }
        /// <summary>
        /// 完成时间
        /// </summary>
        public DateTime FinishTime = DateTime.MinValue;

        /// <summary>
        /// 产品供货商ID 本地数据库ID
        /// </summary>
        public int VendorID = 0;

        [System.Xml.Serialization.XmlIgnore]
        public string VendorCoName = string.Empty;

        /// <summary>
        /// SupplierID ID 本地数据库ID
        /// </summary>
        public int SupplierID = 0;

        [System.Xml.Serialization.XmlIgnore]
        public string SupplierCoName = string.Empty;

        /// <summary>
        /// 产品供货商-联系人
        /// </summary>
        public string VendorContact = string.Empty;

        /// <summary>
        /// 产品供货商-联系电话
        /// </summary>
        public string VendorPhone = string.Empty;

        /// <summary>
        /// 包装供应商-联系人
        /// </summary>
        public string SupplierContact = string.Empty;

        /// <summary>
        /// 包装供应商-联系电话
        /// </summary>
        public string SupploerPhone = string.Empty;

        /// <summary>
        /// 状态 0-新建 1-完成(此档案已经结束)
        /// </summary>
        public int Status = 0;
    }
}

当
CaseVO cVo=new CaseVO();后
我修改了cVo.Extend.Status =1 后
获取cVo.ExtendXml 还是=0 为什么??怎样可以实现我修改任意Extend的属性的时候Case的ExtendXml也跟着变

[我姓区不姓区]

    public class CaseVO
    {
        public int ID = 0;
        public string CaseNo = string.Empty;

        private string m_ExtendXml = string.Empty;
        [JsonIgnore]
        public string ExtendXml
        {
            get
            {
                if(m_ExtendXml == null)
                    m_ExtendXml = SerializationHelper.SerializeToXml(m_Extend);
                return m_ExtendXml;
            }
            set { 
                m_ExtendXml = value;
                m_Extend = (CaseExtendVO)SerializationHelper.DeserializeFromXml(m_ExtendXml, typeof(CaseExtendVO));
            }
        }
        private CaseExtendVO m_Extend = new CaseExtendVO();

        public CaseExtendVO Extend
        {
            get
            {
                if(m_Extend == null)
                    m_Extend = (CaseExtendVO)SerializationHelper.DeserializeFromXml(m_ExtendXml, typeof(CaseExtendVO));
                return m_Extend;
            }
            set
            {
                m_Extend = value;
                m_ExtendXml = SerializationHelper.SerializeToXml(value);
            }
        }
    }

[Dcboy]

楼上的 还是没效果啊~~~~
实现不到 实时改变属性的时候马上序列成xml