Move ListBox items Up and Down with Up and Down Arrow buttons using C# in ASP.Net

Hi donny,

I have created one sample please refer below.

HTML

<div>
    <asp:ListBox ID="lstItems" runat="server" Height="187px" Width="181px" SelectionMode="Multiple">
        <asp:ListItem>Item 1</asp:ListItem>
        <asp:ListItem>Item 2</asp:ListItem>
        <asp:ListItem>Item 3</asp:ListItem>
        <asp:ListItem>Item 4</asp:ListItem>
        <asp:ListItem>Item 5</asp:ListItem>
        <asp:ListItem>Item 6</asp:ListItem>
        <asp:ListItem>Item 7</asp:ListItem>
        <asp:ListItem>Item 8</asp:ListItem>
        <asp:ListItem>Item 9</asp:ListItem>
        <asp:ListItem>Item 10</asp:ListItem>
    </asp:ListBox>
    <br />
    <br />
    <asp:Button ID="btnUp" runat="server" Text="UP" OnClick="btnUp_Click" />
    <asp:Button ID="btnDown" runat="server" Text="DOWN" OnClick="btnDown_Click" />
</div>

Code

protected void btnUp_Click(object sender, EventArgs e)
{
    if (lstItems.SelectedIndex != -1)
    {
        int selectedItemIndex = lstItems.SelectedIndex;
        List<ListItem> selectedItems = new List<ListItem>();
        int repositionIndex = 0;

        foreach (ListItem item in lstItems.Items)
        {
            if (item.Selected)
            {
                selectedItems.Add(item);
            }
        }
        repositionIndex = selectedItemIndex - 1;
        foreach (ListItem item in selectedItems)
        {
            lstItems.Items.Remove(item);
            if (selectedItemIndex != 0)
                lstItems.Items.Insert(repositionIndex, item);
            repositionIndex++;
        }
        if (selectedItemIndex == 0)
        {
            repositionIndex = lstItems.Items.Count;
            foreach (ListItem item in selectedItems)
            {
                lstItems.Items.Insert(repositionIndex, item);
                repositionIndex++;
            }
        }
    }
}

protected void btnDown_Click(object sender, EventArgs e)
{
    if (lstItems.SelectedIndex != -1)
    {
        int selectedItemIndex = lstItems.SelectedIndex;
        List<ListItem> selectedItems = new List<ListItem>();
        int repositionIndex = 0;
        bool isContainLastElement = false;
        foreach (ListItem item in lstItems.Items)
        {
            if (item.Selected)
            {
                if (lstItems.Items.IndexOf(item) == lstItems.Items.Count - 1)
                {
                    isContainLastElement = true;
                }
                selectedItems.Add(item);
            }
        }
        repositionIndex = selectedItemIndex + 1;
        foreach (ListItem item in selectedItems)
        {
            lstItems.Items.Remove(item);
        }

        repositionIndex = isContainLastElement ? 0 : repositionIndex;
        foreach (ListItem item in selectedItems)
        {
            lstItems.Items.Insert(repositionIndex, item);
            repositionIndex++;
        }
    }
}

Screenshot