Unity - 访问事件抛出空异常

Question

我有一个脚本可以从 Hierarchy 访问 Vuforia 的实例化游戏对象并向其添加组件：

IEnumerable<TrackableBehaviour> tbs = TrackerManager.Instance.GetStateManager().GetTrackableBehaviours();

foreach (TrackableBehaviour tb in tbs)
{
if (tb.TrackableName == "Fashion")
{

if (tb.name == "New Game Object")
{

// change generic name to include trackable name
tb.gameObject.name = ++counter + "DynamicImageTarget-" + tb.TrackableName;

// add additional script components for trackable
tb.gameObject.AddComponent<DefaultTrackableEventHandler>();
tb.gameObject.AddComponent<TurnOffBehaviour>();

到这里它还在工作，但是在这个 point/line 当我尝试添加

tb.gameObject.GetComponent<DefaultTrackableEventHandler>().OnTargetFound.AddListener(DressFound);

在运行时抛出 null 异常

当我尝试时

tb.gameObject.GetComponent<DefaultTrackableEventHandler>().OnTargetFound.RemoveAllListeners();

也在运行时抛出 null 异常

然而当我尝试

tb.gameObject.GetComponent<DefaultTrackableEventHandler>().enable = false;

正在运行并禁用脚本组件

void DressFound()
{
augmentation.SetActive(true);

}

为什么我无法访问脚本中的事件？

using UnityEngine;
using UnityEngine.Events;
using Vuforia;

/// <summary>
/// A custom handler that implements the ITrackableEventHandler interface.
///
/// Changes made to this file could be overwritten when upgrading the Vuforia version.
/// When implementing custom event handler behavior, consider inheriting from this class instead.
/// </summary>
public class DefaultTrackableEventHandler : MonoBehaviour
{
    public enum TrackingStatusFilter
    {
        Tracked,
        Tracked_ExtendedTracked,
        Tracked_ExtendedTracked_Limited
    }

    /// <summary>
    /// A filter that can be set to either:
    /// - Only consider a target if it's in view (TRACKED)
    /// - Also consider the target if's outside of the view, but the environment is tracked (EXTENDED_TRACKED)
    /// - Even consider the target if tracking is in LIMITED mode, e.g. the environment is just 3dof tracked.
    /// </summary>
    public TrackingStatusFilter StatusFilter = TrackingStatusFilter.Tracked_ExtendedTracked_Limited;
    public UnityEvent OnTargetFound;
    public UnityEvent OnTargetLost;


    protected TrackableBehaviour mTrackableBehaviour;
    protected TrackableBehaviour.Status m_PreviousStatus;
    protected TrackableBehaviour.Status m_NewStatus;
    protected bool m_CallbackReceivedOnce = false;

    protected virtual void Start()
    {
        mTrackableBehaviour = GetComponent<TrackableBehaviour>();

        if (mTrackableBehaviour)
        {
            mTrackableBehaviour.RegisterOnTrackableStatusChanged(OnTrackableStatusChanged);
        }
    }

    protected virtual void OnDestroy()
    {
        if (mTrackableBehaviour)
        {
            mTrackableBehaviour.UnregisterOnTrackableStatusChanged(OnTrackableStatusChanged);
        }
    }

    void OnTrackableStatusChanged(TrackableBehaviour.StatusChangeResult statusChangeResult)
    {
        m_PreviousStatus = statusChangeResult.PreviousStatus;
        m_NewStatus = statusChangeResult.NewStatus;

        Debug.LogFormat("Trackable {0} {1} -- {2}",
            mTrackableBehaviour.TrackableName,
            mTrackableBehaviour.CurrentStatus,
            mTrackableBehaviour.CurrentStatusInfo);

        HandleTrackableStatusChanged();
    }

    protected virtual void HandleTrackableStatusChanged()
    {
        if (!ShouldBeRendered(m_PreviousStatus) &&
            ShouldBeRendered(m_NewStatus))
        {
            OnTrackingFound();
        }
        else if (ShouldBeRendered(m_PreviousStatus) &&
                 !ShouldBeRendered(m_NewStatus))
        {
            OnTrackingLost();
        }
        else
        {
            if (!m_CallbackReceivedOnce && !ShouldBeRendered(m_NewStatus))
            {
                // This is the first time we are receiving this callback, and the target is not visible yet.
                // --> Hide the augmentation.
                OnTrackingLost();
            }
        }

        m_CallbackReceivedOnce = true;
    }

    protected bool ShouldBeRendered(TrackableBehaviour.Status status)
    {
        if (status == TrackableBehaviour.Status.DETECTED ||
            status == TrackableBehaviour.Status.TRACKED)
        {
            // always render the augmentation when status is DETECTED or TRACKED, regardless of filter
            return true;
        }

        if (StatusFilter == TrackingStatusFilter.Tracked_ExtendedTracked)
        {
            if (status == TrackableBehaviour.Status.EXTENDED_TRACKED)
            {
                // also return true if the target is extended tracked
                return true;
            }
        }

        if (StatusFilter == TrackingStatusFilter.Tracked_ExtendedTracked_Limited)
        {
            if (status == TrackableBehaviour.Status.EXTENDED_TRACKED ||
                status == TrackableBehaviour.Status.LIMITED)
            {
                // in this mode, render the augmentation even if the target's tracking status is LIMITED.
                // this is mainly recommended for Anchors.
                return true;
            }
        }

        return false;
    }

    protected virtual void OnTrackingFound()
    {
        if (mTrackableBehaviour)
        {
            var rendererComponents = mTrackableBehaviour.GetComponentsInChildren<Renderer>(true);
            var colliderComponents = mTrackableBehaviour.GetComponentsInChildren<Collider>(true);
            var canvasComponents = mTrackableBehaviour.GetComponentsInChildren<Canvas>(true);

            // Enable rendering:
            foreach (var component in rendererComponents)
                component.enabled = true;

            // Enable colliders:
            foreach (var component in colliderComponents)
                component.enabled = true;

            // Enable canvas':
            foreach (var component in canvasComponents)
                component.enabled = true;
        }

        if (OnTargetFound != null)
            OnTargetFound.Invoke();
    }

    protected virtual void OnTrackingLost()
    {
        if (mTrackableBehaviour)
        {
            var rendererComponents = mTrackableBehaviour.GetComponentsInChildren<Renderer>(true);
            var colliderComponents = mTrackableBehaviour.GetComponentsInChildren<Collider>(true);
            var canvasComponents = mTrackableBehaviour.GetComponentsInChildren<Canvas>(true);

            // Disable rendering:
            foreach (var component in rendererComponents)
                component.enabled = false;

            // Disable colliders:
            foreach (var component in colliderComponents)
                component.enabled = false;

            // Disable canvas':
            foreach (var component in canvasComponents)
                component.enabled = false;
        }

        if (OnTargetLost != null)
            OnTargetLost.Invoke();
    }
}

Answer 1

问题似乎是，如果组件是通过 AddComponent 在运行时附加的，那么两个 UnityEvent 都没有分配。

通常这些都是由 Unity Inspector 自动分配的，因为它们是序列化的。

为了确保您可以始终使用

简单地初始化它们

public UnityEvent OnTargetFound = new UnityEvent();
public UnityEvent OnTargetLost = new UnityEvent();

Unity - 访问事件抛出空异常

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