Datafield Ui Events

Hi,
Just getting familiar to the dev tools and API. I am trying to get the buttons to respond for a custom Datafield. I can get them to function in an app but nothing seems to happen for a datafield.
Using similar code to the app I use the below in a datafield. Any help would be great. Thanks

xxxApp.mc

class xxxApp extends App.AppBase {
.....
function getInitialView() {
return [ new xxxView(), new BaseInputDelegate() ];
}
.....
}

xxxView.mc
using Toybox.WatchUi as Ui;

class BaseInputDelegate extends Ui.InputDelegate
{
function onKey(evt){
Sys.println("key evt : " + evt.getKey());
}
}