<%@ Register Assembly="AsyncControls" Namespace="DelvingWare.AsyncControls" TagPrefix="dw" %>

<dw:AsyncDropDownList runat="server" ID="drpMain" 
OnSelectedIndexChanged="drpMain_IndexChanged">
    <AsyncListItem Value="one">A List Item</AsyncListItem>
    <AsyncListItem Value="two">Another ListItem</AsyncListItem>
    <AsyncListItem Value="three" Selected="true">One More List Item</AsyncListItem>
</dw:AsyncDropDownList>

<dw:AsyncLabel runat="server" ID="lblMain">Change the selected item.</dw:AsyncLabel>
<br/>

<dw:AsyncButton runat="server" ID="btAdd" 
OnClick="btAdd_Click" 
CssClass="greyButton">Add Item</dw:AsyncButton>

<dw:AsyncButton runat="server" ID="btRemove" 
OnClick="btRemove_Click" 
CssClass="greyButton">Remove Selected Item</dw:AsyncButton>

using System;
using DelvingWare.AsyncControls;
...
protected void Page_Load( object sender, EventArgs e )
{
    if ( !IsPostBack )
    {
        // during initial page load add 5 more items
        for ( int i = 0, num = 0 ; i < 5 ; ++i )
        {
            num = drpMain.Items.Count+1;

            // add the item
            drpMain.Items.Add("List Item "+ num, num.ToString());
        }
    }
}

protected void drpMain_IndexChanged( object sender, AsyncEventArgs ae )
{
    // update the label
    lblMain.Text = "Selected Text: "+ drpMain.SelectedItem.Text +
        " (Value: "+ drpMain.SelectedValue +")";
}

protected void btAdd_Click( object sender, AsyncEventArgs ae )
{        
    if ( drpMain.Items.Count == 20 )
    {
        // display an alert to the user
        AsyncPage.Alert("This demo only allows 20 items.");
        return;
    }

    int itemCount = drpMain.Items.Count+1;

    // add the list item
    drpMain.Items.Add("List Item "+ itemCount, itemCount.ToString(), true);

    //update the label
    lblMain.Text = "Selected Text: "+ drpMain.LastItem.Text +
        " (Value: "+ drpMain.LastItem.Value +")";
}

protected void btRemove_Click( object sender, AsyncEventArgs ae )
{
    if ( drpMain.Items.Count > 0 )
    {
        if ( drpMain.SelectedIndex > -1 )
        {
            // remove the selected item
            drpMain.Items.RemoveAt(drpMain.SelectedIndex);
            
            // update the label
            lblMain.Text = "No item selected.";
        }
        else // display an alert to the user
            AsyncPage.Alert("Please select an item to remove.");
    }
    else // display an alert to the user
        AsyncPage.Alert("No items to remove.");
}

Imports System
Imports DelvingWare.AsyncControls
...

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    If Not IsPostBack Then
        ' during initial page load add 5 more items
        Dim num As Integer = 0
        Do While (i < 5)
            
        Loop
        Dim i As Integer = 0
        i
        num = (drpMain.Items.Count + 1)
        ' add the item
        drpMain.Items.Add(("List Item " + num), num.ToString)
    End If
End Sub

Protected Sub drpMain_IndexChanged(ByVal sender As Object, ByVal ae As AsyncEventArgs)
    ' update the label
    lblMain.Text = ("Selected Text: "  _
                + (drpMain.SelectedItem.Text + (" (Value: "  _
                + (drpMain.SelectedValue + ")"))))
End Sub

Protected Sub btAdd_Click(ByVal sender As Object, ByVal ae As AsyncEventArgs)
    If (drpMain.Items.Count = 20) Then
        ' display an alert to the user
        AsyncPage.Alert("This demo only allows 20 items.")
        Return
    End If
    Dim itemCount As Integer = (drpMain.Items.Count + 1)
    ' add the list item
    drpMain.Items.Add(("List Item " + itemCount), itemCount.ToString, true)
    'update the label
    lblMain.Text = ("Selected Text: "  _
                + (drpMain.LastItem.Text + (" (Value: "  _
                + (drpMain.LastItem.Value + ")"))))
End Sub

Protected Sub btRemove_Click(ByVal sender As Object, ByVal ae As AsyncEventArgs)
    If (drpMain.Items.Count > 0) Then
        If (drpMain.SelectedIndex > -1) Then
            ' remove the selected item
            drpMain.Items.RemoveAt(drpMain.SelectedIndex)
            ' update the label
            lblMain.Text = "No item selected."
        Else
            AsyncPage.Alert("Please select an item to remove.")
        End If
    Else
        AsyncPage.Alert("No items to remove.")
    End If
End Sub