创建一个脚本，你可以命名为CustomTrackableEventHandler, 然后：

• 继承DefaultTrackableEventHandler,
• 重载父类的函数
• 把ImageTarget上的DefaultTrackableEventHandler换成CustomTrackableEventHandler

例子如下：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CustomTrackableEventHandler : DefaultTrackableEventHandler
{
    protected override void OnTrackingFound()
    {
        var o = GameObject.CreatePrimitive(PrimitiveType.Sphere);
        o.transform.SetParent(mTrackableBehaviour.transform);
        o.transform.localPosition = Vector3.zero;
        o.transform.localRotation = Quaternion.identity;
        o.transform.localScale = Vector3.one;
    }
    protected override void OnTrackingLost()
    {
        if (transform.childCount != 0)
            Destroy(transform.GetChild(0).gameObject);
    }
}