OnClientSelectedIndexChanging
The OnClientSelectedIndexChanging client-side event occurs when the selected item is about to be changed. This event can be cancelled.
The event handler receives two parameters:
The instance of the listbox firing the event
An event arguments parameter containing the following methods:
get_item() - returns the item that is about to be selected.
set_cancel() - lets you cancel the event and prevent items from being selected.
get_domEvent() - returns the DOM event object
The example below shows how to ask the user before selecting the item:
function onClientSelectedIndexChangingHandler(sender, e) {
if (!confirm("Are you sure?")) {
e.set_cancel(true);
}
}