DropDown Opens with a Delay
In case of RadComboBox with a high number of Items a brief delay is observable when the drop down is opened for the first time in a page life cycle.The delay is caused by the so called ‘lazy initialization’ mechanism - Item objects are initialized in the latest possible moment in the control life cycle. This is the first time Items are accessed with the get_items() method, which happens automatically right before the drop down opens.
You could avoid this delay, or more specifically 'move' it to the initial page load, by calling get_items early in the page life cycle either for all RadComboBoxes on the page or for individual ones.
The first approach uses the pageLoad function as shown below:
function pageLoad(sender, eventArgs) {
//get an array of all RadComboBoxes on the page
var comboBoxesOnPage = Telerik.Web.UI.RadComboBox.ComboBoxes;
for (var ix = 0; ix < comboBoxesOnPage.length; ix++) {
comboBoxesOnPage[ix].get_items(); //force Item initialization
}
}
The second approach uses the OnClientLoad event of a single RadComboBox:
<script type="text/javascript">
function onLoad(sender, eventArgs) {
sender.get_items(); //force Item initialization
}
</script>
<telerik:RadComboBox RenderMode="Lightweight" ID="RadComboBox1" runat="server" OnClientLoad="onLoad" />