listbos二级联动

1 静态页
     <div> <asp:ListBox ID="list_Client"  runat="server" Width="240" Height="800" 
            SelectionMode="Multiple"></asp:ListBox></div> 
     <div>共有<%=countnum %>条数据 </div>       
     </div>
     <div id="main_ct_lf3">
       <asp:ListBox ID="list_Client2" runat="server" Width="240" Height="800" 
            AutoPostBack="True" onselectedindexchanged="list_Client2_SelectedIndexChanged"></asp:ListBox>
     </div>
     <div id="main_ct_lf2">
        <div><asp:Button ID="sub_but01" runat="server" Text=">>>" 
                onclick="sub_but01_Click" /></div>
        <div><asp:Button ID="Sub_but02" runat="server" Text="|>" /></div>
     </div>
     <div id="main_ct_rt">
     <div><asp:Label ID="lb_type" runat="server"></asp:Label> </div>   
      <div><asp:ListBox ID="list_Client3"  runat="server" Width="240" Height="780" 
            AutoPostBack="True"></asp:ListBox></div>
      <div>共有<%=countnum3%>条数据</div>
      </div>
      <div id="main_ct_rt2">
        <div><asp:Button ID="Button1" runat="server" Text="移除" onclick="Button1_Click" /></div>
        <div> <asp:Button ID="Button3" runat="server" Text="清空所有选项" /></div>
        <div><asp:Button ID="Button2" runat="server" Text="添加到数据库" /></div>
     

      </div> 

2.后台源码

            /// <summary>
        /// 把数据转移到第三个listbox
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void sub_but01_Click(object sender, EventArgs e)
        {
          if (lb_type.Text != list_Client2.SelectedValue)
          {
              list_Client3.Items.Clear();
          }
          // list_Client.Items.Remove(list_Client.SelectedItem);
          foreach (ListItem items in list_Client.Items)
          {
              if (items.Selected)
              {
                  list_Client3.Items.Add(items.Value);


                  // GetDataTable();
              }
          }
          delIDS();
          countnum3 = list_Client3.Items.Count;
          countnum = list_Client.Items.Count;
        }
        /// <summary>
        /// 删除指定的数据
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button1_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < list_Client3.Items.Count; i++)
            {
                list_Client.Items.Remove(list_Client3.SelectedItem);


            }
        }