Vuforia- Implementing ITrackableEventHandler Interface

I am trying to create a script to recognise when an particular image target is found. This will show a UI for that particular image target.

I have experience extending objects in java but I am struggling with C#.

I receive this error in the debug console.

`Vuforia.UIElf' does not implement interface member `Vuforia.ITrackableEventHandler.OnTrackableStateChanged(Vuforia.TrackableBehaviour.Status, Vuforia.TrackableBehaviour.Status)'

I am not completely sure if I am doing this correctly and...

Vuforia- Implementing ITrackableEventHandler Interface