When working with large data sets, it is convenient to use the RadDropDownList Virtual Scrolling functionality. It has similar behavior to as the LOD, but will enables access to items in a non-sequential manner.For instance, if you want to scroll to the bottom of the DropDown, you won’t need to load all the items in between.
At the client-side you are able to access the items that are placed in the drop down list visible area.
To enable Virtual Scrolling for browsing large record sets:
In order to utilize the Virtual Scrolling the DropDownHeight property must be set.
Set the EnableVirtualScrolling property to True.
<telerik:RadDropDownList RenderMode="Lightweight" ID="RadDropDownList1" runat="server" DefaultMessage="Select" DataSourceID="SqlDataSource1" DataTextField="ContactName" DataValueField="CustomerID" EnableVirtualScrolling="true" DropDownHeight="200px"> </telerik:RadDropDownList> <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>" SelectCommand="SELECT [CustomerID], [ContactName] FROM [Customers]"></asp:SqlDataSource>