Event Hundler in ARTrackedImageManager

//ARTrackedImageManager _trackedImageManager;
void Awake()
{
 _trackedImageManager.trackedImagesChanged += _onChange;
}

private void _onChange(ARTrackedImagesChangedEventArgs args){

 List<ARTrackedImage> added      = args.added;
 List<ARTrackedImage> updated    = args.updated;
 List<ARTrackedImage> removed    = args.removed;

}

void Update(){

foreach (ARTrackedImage image in _trackedImageManager.trackables)
{

switch(image.trackingState){
  case UnityEngine.XR.ARSubsystems.TrackingState.Tracking:
    //syori1
    break;
  case UnityEngine.XR.ARSubsystems.TrackingState.Limited:
    //syori2
    break;
  case UnityEngine.XR.ARSubsystems.TrackingState.None:
                        default:
    //syori
    break;

}

}