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 enable 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.
Virtual Scroll Rendering
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>
Virtual scrolling relies on element dimensions. This means that the RadDropDownList element must be rendered by the browser, so it must not be hidden (for example, it must not be in a container with
display:none). Otherwise, the virtual scrolling will fail to initialize properly and it will throw errors either during initialization, or during use. A prime example of a scenario that will cause such problems is placing a RadDropDownList in a RadGrid with batch editing mode.