急！急！急不知道咋获取所选中的checkbox的值

各位前辈，小弟刚入江湖，就遇到以下问题，请高手帮忙看下我该咋写呀！

aspx代码如下：


<script type="text/javascript">
//Checkbox全选
function SelectAllCheckboxes(obj){
var theTable = obj.parentNode.parentNode.parentNode;
var inputs = theTable.getElementsByTagName('input');
for(var i = 0;i<inputs.length;i++) {
if(inputs[i].type == "checkbox") {
inputs[i].checked = obj.checked;
}
}
}

/***********************检查编辑按钮******************************/
function EditButton()
{
checkCount = 0;
var checkedBoxValues = GetCheckedBoxValues();

if(checkedBoxValues == "0")
{
alert("请选择要操作的记录！");
return false;
}else if(checkCount > 1)
{
alert("你每次只能选择一条记录操作！");
return false;
}else
{
document.getElementById("CheckGuid").value = checkedBoxValues.replace('0,','');
return true;
}
}

/***********************检查删除按钮******************************/
function DeleteButton()
{

var checkedBoxValues = GetCheckedBoxValues();
if(checkedBoxValues == "0")
{
alert("请选择要删除的记录！");
return false;
}else if(window.confirm("你确定要删除吗?"))
{
document.getElementById("CheckGuid").value = checkedBoxValues.replace('0,','');
return true;
}else
{
return false;
}
}

/***********************得到选中的CheckBox的行绑定的值，如Eval("ML_Id")******************************/
function GetCheckedBoxValues()
{
var checkedBoxValues = "0";
var inputs = document.getElementsByTagName("input");
for(var j = 0 ; j < inputs.length ; j++){
if(inputs[j].type == "checkbox" && inputs[j].id != "checkboxAll"){
if(inputs[j].checked == true){
checkedBoxValues +=( "," +"'"+inputs[j].value+"'");
checkCount++;
}
}
}
return checkedBoxValues;
}

</script>

<div runat="server">
<fieldset>
<legend>---会员等级---</legend>
<asp:GridView runat="server" ID="gvlist" AutoGenerateColumns="False" CellPadding="4"
ForeColor="#333333" GridLines="None" Width="98%">
<FooterStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
<RowStyle BackColor="#EFF3FB" HorizontalAlign="Center" BorderStyle="Dotted" />
<Columns>
<asp:TemplateField>
<HeaderTemplate>
<input type="checkbox" id="checkboxAll" onclick="javascript:SelectAllCheckboxes(this);" />
</HeaderTemplate>
<ItemTemplate>
<input type="checkbox" id="checkboxItem" value='<%#Eval("ML_Id") %>' />
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="ML_Name" HeaderText="会员等级" />
<asp:BoundField DataField="ML_Integralpoint" HeaderText="积分满足点" />
<asp:BoundField DataField="ML_Tradingposts" HeaderText="交易满足点" />
<asp:BoundField DataField="ML_Leveldiscount" HeaderText="等级折扣" />
<asp:BoundField DataField="ML_default" HeaderText="是否默认等级" />
</Columns>
<PagerStyle BackColor="#2461BF" ForeColor="White" HorizontalAlign="Center" />
<SelectedRowStyle BackColor="#D1DDF1" Font-Bold="True" ForeColor="#333333" />
<HeaderStyle BackColor="#507CD1" Font-Bold="True" ForeColor="White" />
<EditRowStyle BackColor="#2461BF" />
<AlternatingRowStyle BackColor="White" />
</asp:GridView>
</fieldset>
</div>
<div>
<p>
<asp:Button runat="server" ID="btnAdd" Text="添加" CssClass="bt2" PostBackUrl="~/Admin/MemberManage/MemberLevelEdit.aspx" />  <asp:Button
runat="server" ID="btnEdit" Text="编辑" CssClass="bt2" CausesValidation="false"
OnClientClick="return EditButton()" />  
<asp:Button runat="server" ID="btnDelete" Text="删除" CssClass="bt2" CausesValidation="false"
OnClientClick="return DeleteButton()" OnClick="btnDelete_Click" /></p>
<asp:HiddenField ID="CheckGuid" runat="server" Value="0" />
</div>





aspx.cs代码如下：



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;

public partial class Admin_MemberManage_MemberLevel : System.Web.UI.Page
{

/// <summary>
/// 绑定
/// </summary>
public void bind()
{
gvlist.DataSource = BLL.MemberLevelBll.MemberLevel_Select();
gvlist.DataBind();

}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
bind();
}
}
/// <summary>
/// 删除
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void btnDelete_Click(object sender, EventArgs e)
{
for (int i = 0; i < gvlist.Rows.Count;i++ )
{

CheckBox cb = ((CheckBox)gvlist.Rows[i].FindControl("checkboxItem")) as CheckBox;
if (cb != null && cb.Checked)
{
HiddenField hid = ((HiddenField)gvlist.Rows[i].FindControl("CheckGuid")) as HiddenField;
if (hid != null)
{
int mid = Convert.ToInt32(hid.Value);
BLL.MemberLevelBll.MemberLevel_Delete(mid);
}
}
}

bind();
}
/// <summary>
/// 编辑
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void btnEdit_Click(object sender, EventArgs e)
{
for (int i = 0; i < gvlist.Rows.Count; i++)
{

CheckBox cb = ((CheckBox)gvlist.Rows[i].FindControl("checkboxItem")) as CheckBox;
if (cb != null && cb.Checked)
{
HiddenField hid = ((HiddenField)gvlist.Rows[i].FindControl("CheckGuid")) as HiddenField;
if (hid != null)
{
int mid = Convert.ToInt32(hid.Value);
Response.Redirect("MemberLevel.aspx?ML_Id='" + mid + "'");
}
}
}
}

}

js代码都没问题，就是编辑和删除时选中的checkbox值为空，总之一句话就是我不知道咋获取选中checkbox的值，望各位前辈指点迷津啊。