public string OnClientDropDownOpening { get; set; }

Public Property OnClientDropDownOpening As String
	Get
	Set

public:
property String^ OnClientDropDownOpening {
	String^ get ();
	void set (String^ value);
}

member OnClientDropDownOpening : string with get, set

<script language="javascript">               

function HandleOpen(sender,args)
{
    if (someCondition)
    {
        args.set_cancel(true);   
    }
    else
    {
        alert("Opening combobox with " + comboBox.get_items().get_count() + " items");
    }
}

</script>


<kettic:kaxcombobox 
      id="KaxComboBox1" 
      Runat="server" 
      OnClientDropDownOpening="HandleOpen">
</kettic:kaxcombobox>