New to Telerik UI for ASP.NET AJAX? Download free 30-day trial


The following article demonstrates the usage of the ItemsRequested event of the RadListBox

The ItemsRequested event is triggered when the EnabledLoadOnDemand property is True or when the scroll bar is used to request additional portion of items. The event will be also fired, if you explicitly call the requestItems client-side method of the RadListBox.

ItemsRequested event handler receives two arguments:

  1. The RadListBox that is loading the items. This argument is of type object, but can be cast to the RadListBox type.

  2. The RadListBoxItemsRequestedEventArgs object, which has the following properties:

  • StartIndex - should be passed from the requestItems() client-side method to specify the current number of Items, loaded in the RadListBox.

  • Count - should be passed from the requestItems() client-side method to specify the desired number of Items per request.

<telerik:radlistbox runat="server"
            Text="Load Next Portion"
<script type="text/javascript">
    function OnClientClicked(sender, eventArgs) {
        var listBox = $find("RadListBox1");
        var loadedItemsCount = listBox.get_items().get_count();
        var itemsPerRequest = 10;
        listBox.requestItems(loadedItemsCount, itemsPerRequest);
protected void RadListBox1_ItemsRequested(object sender, RadListBoxItemsRequestedEventArgs e)
    int maxItemsToLoad = 100;

    int endOffset = Math.Min(e.StartIndex + e.Count, maxItemsToLoad);

    for (int i = e.StartIndex; i < endOffset; i++)
        RadListBox1.Items.Add(new RadListBoxItem("RadListBoxItem" + i.ToString(), "Value" + i.ToString()));
Protected Sub RadListBox1_ItemsRequested(sender As Object, e As RadListBoxItemsRequestedEventArgs)
    Dim maxItemsToLoad As Integer = 100

    Dim endOffset As Integer = Math.Min(e.StartIndex + e.Count, maxItemsToLoad)

    For i As Integer = e.StartIndex To endOffset - 1
        RadListBox1.Items.Add(New RadListBoxItem("RadListBoxItem" + i.ToString(), "Value" + i.ToString()))
End Sub
In this article