ASP.NET ListBox 左右移動 C#

<asp:Button ID="btMoveRight" runat="server" Text=" &gt;&gt; " OnClick="btMoveRight_Click" />
<asp:Button ID="btMoveLeft" runat="server" Text=" &lt;&lt; " OnClick="btMoveLeft_Click" />

// 右移按鍵的函式
protected void btMoveRight_Click(object sender, EventArgs e)
{
 // 將所選到的項目新增至lbGroupUser
 for (int i = 0; i < lbNotGroupUser.Items.Count; i++)
 {
  if (lbNotGroupUser.Items[i].Selected)
  {
   lbGroupUser.Items.Add(lbNotGroupUser.Items[i]);
   lbNotGroupUser.Items.RemoveAt(i);
   i--;
  }
 }
 lbGroupUser.ClearSelection();
}

//左移按鍵的函式
protected void btMoveLeft_Click(object sender, EventArgs e)
{
 // 將所選到的項目新增至lbNotGroupUser
 for (int i = 0; i < lbGroupUser.Items.Count; i++)
 {
  if (lbGroupUser.Items[i].Selected)
  {
   lbNotGroupUser.Items.Add(lbGroupUser.Items[i]);
   lbGroupUser.Items.RemoveAt(i);
   i--;
  }
 }
 lbNotGroupUser.ClearSelection();
}