我的DataGrid嵌套DataList(未解决)

我觉得我的例子和MSDN (saucer(思归)版)的大概是一致的，个人觉得问题出在为什么我的页面的dlReplyList在绑定前（就是击编辑按钮后）会是“未定义的值”的？如下图（上半）：而saucer(思归)版的例子，在同一个断点，DataList实例ItemsList却是存在的（下半）


页面框架：

<asp:DataGrid Width="80%"
DataKeyField="PostId" ID="dgPostList" runat="server"
AllowPaging="True" PageSize="10" AutoGenerateColumns="false"
OnPageIndexChanged="TrunPage" OnEditCommand="EditPost"
OnDeleteCommand=DeletePost OnUpdateCommand=UpdatePost OnCancelCommand=CancelPost>
<pagerstyle Mode="NumericPages" Position="TopAndBottom" HorizontalAlign="Center"></pagerstyle>

<columns>
<asp:TemplateColumn>
<itemtemplate>
<table id="tbPostRecord" bgcolor="#dfdfdf" width="100%">
...
<div align="right">
<asp:ImageButton runat="server" ID="imgbtEdit" CommandName="edit" ImageUrl="images/edit.gif" AlternateText="编辑"></asp:ImageButton>
<asp:ImageButton runat="server" ID="imgbtDelete" CommandName="delete" ImageUrl="images/del.gif" AlternateText="删除"></asp:ImageButton>
......

<asp:DataList ID="dlReplyList" Width="100%" RepeatColumns=1
DataKeyField="PostId" RepeatDirection=Vertical runat="server"
OnEditCommand="EditReply" OnDeleteCommand=DeleteReply
OnUpdateCommand=UpdateReply OnCancelCommand=CancelReply
DataSource=''<%# GetReplyData((int)DataBinder.Eval(Container.DataItem, "PostID"))%>''>

<itemtemplate>
<table id="tbReplyRecord" width="100%">
.....

<asp:ImageButton runat="server" ID="imgbtEdit2" CommandName="edit" ImageUrl="images/edit.gif" AlternateText="编辑"></asp:ImageButton>
<asp:ImageButton runat="server" ID="imgbtDelete2" CommandName="delete" ImageUrl="images/del.gif"
AlternateText="删除"></asp:ImageButton>
.......

</table>
</itemtemplate>
<EditItemTemplate>

<table id="tbReplyRecordEdit" width="100%">
..........
<asp:ImageButton runat="server" ID="imgbtSave" CommandName="update" ImageUrl="images/save.jpg" AlternateText="保存"></asp:ImageButton>
<asp:ImageButton runat="server" ID="imgbtCancel" CommandName="cancel" ImageUrl="images/cancel.jpg" AlternateText="取消"></asp:ImageButton>
...

</table>
</EditItemTemplate>
</asp:DataList>


</itemtemplate>
<EditItemTemplate>
<table id="tbPostRecordedit" bgcolor="#dfdfdf" width="100%">
.......
<asp:ImageButton runat="server" ID="imgbtSavePost" CommandName="update" ImageUrl="images/save.jpg"
AlternateText="保存"></asp:ImageButton>
<asp:ImageButton runat="server" ID="imgbtCancelPost" CommandName="cancel" ImageUrl="images/cancel.jpg" AlternateText="取消"></asp:ImageButton>
.........
</table>
</EditItemTemplate>
</asp:TemplateColumn>


</columns>
</asp:DataGrid>





后台代码，看有色部分

using System;
using System.Data;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using fiveXdotNet.BLL;

namespace fiveXdotNet.Web
{
/// <summary>
/// index 的摘要说明。
/// </summary>
public class index : ScrollPage
{
protected System.Web.UI.WebControls.Label lblName;
protected System.Web.UI.WebControls.Label lblPostId;
protected System.Web.UI.WebControls.Label lblPostTime;
protected System.Web.UI.WebControls.Label lblContent;
protected System.Web.UI.WebControls.Label lblPosterName;
protected System.Web.UI.WebControls.Label lblReplyTime;
protected System.Web.UI.WebControls.Label lblReplyContent;
protected System.Web.UI.WebControls.DataGrid dgPostList;
protected System.Web.UI.WebControls.DataList dlReplyList;
protected System.Web.UI.HtmlControls.HtmlTextArea txaNewPost;
protected DataSet _ds = new DataSet();

private void Page_Load(object sender, System.EventArgs e)
{
if(!Page.IsPostBack){
bind();
}
//string s = this.Request.Form["txaNewPost"];
//string s01 = this.Request.Form["txt01"];
//string s02 = this.Request.Form["txaNewPost"];
}

private void bind(){
Post.getAllPost(ref _ds);
DataView dvPostList = new DataView(_ds.Tables[0], "PostType = 0","PostID desc",DataViewRowState.CurrentRows);
dgPostList.DataSource = dvPostList;
dgPostList.DataBind();
}
protected DataView GetReplyData(int iPostId){
DataView dvPostList = new DataView(_ds.Tables[0],"PostType = " + iPostId.ToString(),"PostID",DataViewRowState.CurrentRows);
//DataView dvPostList = new DataView(_ds.Tables[0]);
//dvPostList.RowFilter = "PostType = " + iPostId.ToString();
return dvPostList;
}

protected void TrunPage(object sender, DataGridPageChangedEventArgs e){
dgPostList.CurrentPageIndex = e.NewPageIndex;
dgPostList.EditItemIndex = -1;
this.bind();
}
protected void EditReply(object sender, System.Web.UI.WebControls.DataListCommandEventArgs e){
DataList dlReplyList = (DataList)sender;
dlReplyList.EditItemIndex = e.Item.ItemIndex;
dgPostList.EditItemIndex = -1;
DataGridItem dgi = (DataGridItem)dlReplyList.Parent.Parent;
int n = dgi.ItemIndex;
int nPostID = (int)dgPostList.DataKeys[n];
Post.getAllPost(ref _ds);
dlReplyList.DataSource = GetReplyData(nPostID);
dlReplyList.DataBind();
//dl.DataBind();
//dlReplyList.EditItemIndex = e.Item.ItemIndex;
//this.dlReplyList = dl;
//Post.getAllPost(ref _ds);
//this.dlReplyList.DataSource = GetReplyData(22);
//this.dlReplyList.DataBind();
//this.bind();
}
protected void EditPost(object sender, System.Web.UI.WebControls.DataGridCommandEventArgs e){
dgPostList.EditItemIndex = e.Item.ItemIndex;
this.bind();
}
protected void AddPost(object sender, System.Web.UI.ImageClickEventArgs e){
//string sContent = this.txaNewPost.Value.ToString();//为什么用编程方式取不到值的？
string sContent = this.Request.Form["txaNewPost"];
//Session["ClassmateId"] = 1;
Post post = new Post(Convert.ToInt32(Session["ClassmateId"]), DateTime.Now, 0, sContent);
post.Add();
this.bind();
}

public void DeletePost(object sender, DataGridCommandEventArgs e)
{
int iPostId = Convert.ToInt32(dgPostList.DataKeys[(int)e.Item.ItemIndex]);
Post.Delete(iPostId);
this.bind();
}
public void DeleteReply(object sender, DataListCommandEventArgs e)
{
int iPostId = Convert.ToInt32(dlReplyList.DataKeys[(int)e.Item.ItemIndex]);
Post.Delete(iPostId);
this.bind();
}
public void UpdatePost(object sender, DataGridCommandEventArgs e)
{
int iPostId = Convert.ToInt32(dgPostList.DataKeys[(int)e.Item.ItemIndex]);
string sContent = ((TextBox)e.Item.FindControl("txtPostContent")).Text;
DateTime dtPostTime = DateTime.Now;
Post post = new Post(iPostId, dtPostTime, sContent);
post.Update();
dgPostList.EditItemIndex = -1;
this.bind();
}

public void UpdateReply(object sender, DataListCommandEventArgs e)
{
int iPostId = Convert.ToInt32(dlReplyList.DataKeys[(int)e.Item.ItemIndex]);
string sContent = ((TextBox)e.Item.FindControl("txtReplyConten")).Text;
DateTime dtPostTime = DateTime.Now;
Post post = new Post(iPostId, dtPostTime, sContent);
post.Update();
dlReplyList.EditItemIndex = -1;
this.bind();
}

public void CancelPost(object sender, DataGridCommandEventArgs e)
{
dgPostList.EditItemIndex = -1;
this.bind();
}
public void CancelReply(object sender, DataListCommandEventArgs e)
{
dlReplyList.EditItemIndex = -1;
this.bind();
}
#region Web 窗体设计器生成的代码
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。
//
InitializeComponent();
base.OnInit(e);
}

/// <summary>
/// 设计器支持所需的方法 - 不要使用代码编辑器修改
/// 此方法的内容。
/// </summary>
private void InitializeComponent()
{
this.Load += new System.EventHandler(this.Page_Load);

}
#endregion
}
}