多选列表框

<asp:ListBox id="ListBox1" style="Z-INDEX: 100; LEFT: 256px; POSITION: absolute; TOP: 120px"
                runat="server" SelectionMode="Multiple" Width="73px" Height="134px">
                <asp:ListItem Value="1">1</asp:ListItem>
                <asp:ListItem Value="2">2</asp:ListItem>
                <asp:ListItem Value="3">3</asp:ListItem>
                <asp:ListItem Value="4">4</asp:ListItem>
                <asp:ListItem Value="5">5</asp:ListItem>
                <asp:ListItem Value="6">6</asp:ListItem>
            </asp:ListBox>
            <asp:Label id="Label2" style="Z-INDEX: 107; LEFT: 448px; POSITION: absolute; TOP: 96px" runat="server">列表框2</asp:Label>
            <asp:ListBox id="ListBox2" style="Z-INDEX: 101; LEFT: 440px; POSITION: absolute; TOP: 120px"
                runat="server" SelectionMode="Multiple" Width="72px" Height="134px"></asp:ListBox>
            <asp:Button id="Upbtn" style="Z-INDEX: 102; LEFT: 360px; POSITION: absolute; TOP: 136px" runat="server"
                Text="上移"></asp:Button>
            <asp:Button id="Movebtn" style="Z-INDEX: 103; LEFT: 360px; POSITION: absolute; TOP: 176px" runat="server"
                Text="转移"></asp:Button>
            <asp:Button id="Downbtn" style="Z-INDEX: 104; LEFT: 360px; POSITION: absolute; TOP: 216px" runat="server"
                Text="下移"></asp:Button>
            <asp:Label id="Label1" style="Z-INDEX: 106; LEFT: 264px; POSITION: absolute; TOP: 96px" runat="server">列表框1</asp:Label>

        private void Movebtn_Click(object sender, System.EventArgs e)
        {
            int Count = ListBox1.Items.Count;
            int Index = 0;
            for (int i=0;i< Count;i++)
            {
                ListItem Item = ListBox1.Items[Index];
                if (ListBox1.Items[Index].Selected==true)
                {
                    ListBox1.Items.Remove(Item);
                    ListBox2.Items.Add(Item);
                    Index--;
                }
                Index++;
            }
        }

        private void Upbtn_Click(object sender, System.EventArgs e)
        {
            //若不是第一行则上移
            if( ListBox1.SelectedIndex > 0 )
            {
                string name = ListBox1.SelectedItem.Text;
                string ID = ListBox1.SelectedItem.Value;

                int index = ListBox1.SelectedIndex;

                ListBox1.SelectedItem.Text = ListBox1.Items[index-1].Text;
                ListBox1.SelectedItem.Value = ListBox1.Items[index-1].Value;
                ListBox1.Items[index-1].Text = name;
                ListBox1.Items[index-1].Value = ID;
                ListBox1.SelectedIndex --;
            }
        }

        private void Downbtn_Click(object sender, System.EventArgs e)
        {
            //若不是最后一行则下移
            if( ListBox1.SelectedIndex >= 0 && ListBox1.SelectedIndex < ListBox1.Items.Count-1 )
            {
                string name = ListBox1.SelectedItem.Text;
                string ID = ListBox1.SelectedItem.Value;
                int index = ListBox1.SelectedIndex;
                ListBox1.SelectedItem.Text = ListBox1.Items[index+1].Text;
                ListBox1.SelectedItem.Value = ListBox1.Items[index+1].Value;
                ListBox1.Items[index+1].Text = name;
                ListBox1.Items[index+1].Value = ID;
                ListBox1.SelectedIndex ++;
            }