The OnClientDropDownOpening client-side event occurs before the drop-down list opens.

The event handler receives two parameters:

1. The instance of the combobox firing the event.

2. An eventArgs parameter containing the following methods:

   • set_cancel lets you prevent the drop-down from opening.

   • get_domEvent() returns the DOM event object of the drop-down opening.

The example below shows how to prevent the drop-down list from opening when there are no items to be displayed:

CopyASPX

<script language="javascript" type="text/javascript">
    function OnClientDropDownOpening(sender, eventArgs) {
        if (sender.get_items().get_count() == 0) 
        eventArgs.set_cancel(true);
    }
</script>
<telerik:radcombobox 
    id="RadComboBox1" 
    runat="server" 
    onclientdropdownopening="OnClientDropDownOpening">
</telerik:radcombobox>