Caching Items

The EnableItemCaching property of RadComboBox can be used only in Load-on-demand scenario.

When EnableItemCaching is set to True (by default it is False), the combobox will cache the items returned for every request. This means that if you type a given text and the combobox returns some items - they will be cached and the next time you type the same text - the ItemsRequested server-side event will not fire, but the items will load from the cache. This will decrease the server round-trips and improve the performance in cases where the number of items is huge.

Here is a simple example:

<telerik:radcombobox 
    id="RadComboBox4" 
    runat="server" 
    enableitemcaching="True" 
    enableloadondemand="True"
    onitemsrequested="RadComboBox4_ItemsRequested">
</telerik:radcombobox>
<asp:SqlDataSource ID="SqlDataSource1" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
    runat="server">
</asp:SqlDataSource>

protected void RadComboBox4_ItemsRequested(object o, RadComboBoxItemsRequestedEventArgs e) 
{
    RadComboBox4.DataSourceID = "SqlDataSource1"; 
    string selectCommand = "SELECT * FROM CUSTOMERS WHERE CompanyName LIKE '" + e.Text + "%'"; 
    SqlDataSource1.SelectCommand = selectCommand; 
    RadComboBox4.DataTextField = "CompanyName"; RadComboBox4.DataBind(); 
}

Protected Sub RadComboBox4_ItemsRequested(ByVal o As Object, ByVal e As RadComboBoxItemsRequestedEventArgs) Handles RadComboBox4.ItemsRequested
    RadComboBox4.DataSourceID = "SqlDataSource1"
    Dim selectCommand As String = "SELECT * FROM CUSTOMERS WHERE CompanyName LIKE '" + e.Text + "%'"
    SqlDataSource1.SelectCommand = selectCommand
    RadComboBox4.DataTextField = "CompanyName"
    RadComboBox4.DataBind()
End Sub

Here is how the caching works:

1. Open the drop-down list. The ItemsRequested server-side event fires (e.Text = "") and adds all customers to the list. These items are now cached.

2. Type something in the combobox, e.g. "s" - the ItemsRequested server-side event fires (e.Text = "s") and adds all customers which names starts with "s" to the list. These items are cached now.

3. Type another character, e.g. "sa" - the ItemsRequested server-side event fires (e.Text = "sa") and adds all customers which names starts with "sa" to the list. These items are cached now.

4. Click on the Backspace button - this will leave the "s" letter in the input. Instead of firing the ItemsRequested server-side event again - the combobox will take the items from the cache (point 2) and load them without going to the server.

5. Click on the Backspace button again - this will leave the input empty. Instead of firing the ItemsRequested server-side event again - the combobox will take the items from the cache (point 1) and load them without going to the server.

See Also

• Overview