var picker:DatePicker = new DatePicker();
picker.addEventListener(DatePickerEvent.SELECT, selectHandler);
picker.addEventListener(DatePickerEvent.CANCEL, cancelHandler);

private function selectHandler(event:DatePickerEvent):void
{
  trace(event.date); // <- selected date;
}

private function cancelHandler(event:DatePickerEvent):void
{
  trace("Canceled");
}