如何检查当前显示的ImageTarget是否等于随机选择的ImageTarget

我发布了Quiz.cs脚本，在其中我选择了一个随机游戏对象。现在在DefaultTrackableEventHandler中，我需要检查随机选择的游戏对象的ImageTarget是否等于向相机显示的ImageTarget！

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using Vuforia;
public class Quiz : MonoBehaviour 
{
     public GameObject[] models;
     public GameObject currentPoint;
     int index;
     public AudioSource correctAudio;
     public AudioSource notcorrectAudio;
    //QuizLogic test ;
    //public ImageTargetBehaviour checck;
    //private TrackableBehaviour mTrackable;
    //public GameObject[] sounds;
    void Start()
    { 
        StateManager sm = TrackerManager.Instance.GetStateManager();
        IEnumerable<TrackableBehaviour> activeTrackables = sm.GetActiveTrackableBehaviours();
        models = GameObject.FindGameObjectsWithTag("numbers");
        index = Random.Range (0, models.Length);
        currentPoint = models[index];
        print ("Trackable " +currentPoint.name);
        currentPoint.GetComponent<AudioSource> ().Play ();
        foreach (TrackableBehaviour tb in activeTrackables) 
        {
            // As you iterate, you compare with current game object name
            // if you have 3 and 5 and target object is 5 then you get a match.
            if( tb.GetComponent<ImageTargetBehaviour>().ImageTarget.Name==currentPoint.GetComponent<ImageTargetBehaviour>().ImageTarget.Name )
            { 
                print ("Congratulations you have chosen the correct ImageTarget");
            }
            else
            { 
                print ("Try another one !");
            }
        }
}
}

现在，当我将此脚本调用到DefaultTrackableEventHandler.cs中的OnTrackingFound（）中时（当我向相机显示ImageTarget以将其与随机选择的ImageTarget进行比较时），我会得到以下错误：NullReferenceException：对象引用未设置为对象的实例

这是DefaultTrackableEventHandler.cs:

using UnityEngine;
namespace Vuforia
{
    /// <summary>
    /// A custom handler that implements the ITrackableEventHandler interface.
    /// </summary>
    public class QuizLogic : MonoBehaviour,
    ITrackableEventHandler
    {
        #region PRIVATE_MEMBER_VARIABLES
        private TrackableBehaviour mTrackableBehaviour;

        #endregion // PRIVATE_MEMBER_VARIABLES

        Quiz quiz;

        #region UNTIY_MONOBEHAVIOUR_METHODS
        void Start()
        {
            mTrackableBehaviour = GetComponent<TrackableBehaviour>();
            if (mTrackableBehaviour)
            {
                mTrackableBehaviour.RegisterTrackableEventHandler(this);
            }
        }
        #endregion // UNTIY_MONOBEHAVIOUR_METHODS

        #region PUBLIC_METHODS
        public GameObject show;
        public GameObject hide;
        /// <summary>
        /// Implementation of the ITrackableEventHandler function called when the
        /// tracking state changes.
        /// </summary>
        public void OnTrackableStateChanged(
            TrackableBehaviour.Status previousStatus,
            TrackableBehaviour.Status newStatus)
        {
            if (newStatus == TrackableBehaviour.Status.DETECTED ||
                newStatus == TrackableBehaviour.Status.TRACKED ||
                newStatus == TrackableBehaviour.Status.EXTENDED_TRACKED )
            {
                OnTrackingFound();

            }
            else
            {
                OnTrackingLost();
            }
        }
        #endregion // PUBLIC_METHODS

        #region PRIVATE_METHODS

        private void OnTrackingFound()
        {
            show.SetActive(true);
            Renderer[] rendererComponents = GetComponentsInChildren<Renderer>(true);
            Collider[] colliderComponents = GetComponentsInChildren<Collider>(true);
            AudioSource[] audiocomponents  = GetComponentsInChildren<AudioSource>(true);
            // Enable rendering:
            foreach (Renderer component in rendererComponents)
            {
                component.enabled = true;
            }

            // Enable colliders:
            foreach (Collider component in colliderComponents)
            {
                component.enabled = true;
            }
            //Enable AudioSource 
            foreach (AudioSource component in audiocomponents)
            {
                component.enabled = true;
            }
            Debug.Log("Trackable " + mTrackableBehaviour.TrackableName + " found");
            quiz.GetComponent<Quiz> ();
        }

        private void OnTrackingLost()
        {
            hide.SetActive(true);
            Renderer[] rendererComponents = GetComponentsInChildren<Renderer>(true);
            Collider[] colliderComponents = GetComponentsInChildren<Collider>(true);
            AudioSource[] audiocomponents  = GetComponentsInChildren<AudioSource>(true);
            // Disable rendering:
            foreach (Renderer component in rendererComponents)
            {
                component.enabled = false;
            }
            // Disable colliders:
            foreach (Collider component in colliderComponents)
            {
                component.enabled = false;
            }

            //Disable AudioSource
            //foreach (AudioSource component in audiocomponents)
            //{
            //  component.enabled = false;
            //}

            Debug.Log("Trackable " + mTrackableBehaviour.TrackableName + " lost");
        }

        #endregion // PRIVATE_METHODS
    }
}

请帮我做这件事，因为我是Vuforia的新手！！！如果您能帮助