Unity 2D中如何检测GameObject列表内的对象是否已被销毁

需求背景 #

• 维护GameObject类型的敌人列表，实现所有敌人被消灭前战斗屏障保持锁定的效果，敌人列表设置为public类型方便后续复用这套逻辑
• 现有触发逻辑：玩家碰撞到屏障触发区域时，遍历敌人列表统计存活敌人数量：
  • 仍有敌人存活：启用战斗屏障碰撞体、切换为屏障显示精灵
  • 敌人全部被消灭：禁用屏障碰撞体、切换为无屏障的消失精灵
• 待补全逻辑：for循环内的判断条件，需要检测列表中对应敌人GameObject是否已被销毁（引用失效、对象不存在/Inspector面板显示为None）

原有待补全代码 #

public GameObject fightBarrier;
public List<GameObject> enemies = new List<GameObject>();
public SpriteRenderer Barrier_0;
public SpriteRenderer Barrier_1;
public SpriteRenderer Barrier_2;
public SpriteRenderer Barrier_3;
public Sprite Barrier;
public Sprite noBarrier;

private int enemiesAmountCheck;

// overrided because it's inheriting from another script
protected override void OnCollide(Collider2D coll)
{
   if (coll.name == "Player")
   {
      enemiesAmountCheck = enemies.Count;
      for (int i = 0; i < enemies.Count - 1; i++)
      {
         // This if statement has to check if the GameObject doesn't exist (AKA the GameObject is None)
         if (enemies[i]... )
         {
            enemiesAmountCheck = enemiesAmountCheck - 1;
         }
      }
      if (enemiesAmountCheck > 0)
      {
         fightBarrier.GetComponent<BoxCollider2D>().enabled = true;
         Barrier_0.sprite = Barrier;
         Barrier_1.sprite = Barrier;
         Barrier_2.sprite = Barrier;
         Barrier_3.sprite = Barrier;
      }
      else
      {
         fightBarrier.GetComponent<BoxCollider2D>().enabled = false;
         Barrier_0.sprite = noBarrier;
         Barrier_1.sprite = noBarrier;
         Barrier_2.sprite = noBarrier;
         Barrier_3.sprite = noBarrier;
      }
   }
}

补全方案 #

核心判断条件 #

Unity对UnityEngine.Object（GameObject的直接基类）重载了==运算符，直接判断enemies[i] == null即可同时覆盖两种失效场景：

• 列表元素本身未在Inspector面板赋值，对应字段显示为None
• 敌人GameObject已经被Destroy()方法销毁，引擎原生层对象已释放

补全后的if判断为：

if (enemies[i] == null)
{
    enemiesAmountCheck--;
}

原有代码bug修复 #

原for循环的边界条件写为i < enemies.Count - 1，会漏掉列表最后一个敌人的检测，需要修改为i < enemies.Count才能遍历所有列表元素，否则会出现敌人全灭但屏障仍锁定的异常。

补全后完整逻辑代码 #

public GameObject fightBarrier;
public List<GameObject> enemies = new List<GameObject>();
public SpriteRenderer Barrier_0;
public SpriteRenderer Barrier_1;
public SpriteRenderer Barrier_2;
public SpriteRenderer Barrier_3;
public Sprite Barrier;
public Sprite noBarrier;

private int enemiesAmountCheck;

// overrided because it's inheriting from another script
protected override void OnCollide(Collider2D coll)
{
   if (coll.name == "Player")
   {
      enemiesAmountCheck = enemies.Count;
      // 修复循环边界，遍历所有敌人条目
      for (int i = 0; i < enemies.Count; i++)
      {
         // 检测敌人对象是否未赋值/已被销毁
         if (enemies[i] == null)
         {
            enemiesAmountCheck--;
         }
      }
      if (enemiesAmountCheck > 0)
      {
         fightBarrier.GetComponent<BoxCollider2D>().enabled = true;
         Barrier_0.sprite = Barrier;
         Barrier_1.sprite = Barrier;
         Barrier_2.sprite = Barrier;
         Barrier_3.sprite = Barrier;
      }
      else
      {
         fightBarrier.GetComponent<BoxCollider2D>().enabled = false;
         Barrier_0.sprite = noBarrier;
         Barrier_1.sprite = noBarrier;
         Barrier_2.sprite = noBarrier;
         Barrier_3.sprite = noBarrier;
         // 可选优化：清空列表内的空引用，避免后续重复遍历无效元素
         enemies.RemoveAll(enemy => enemy == null);
      }
   }
}

优化说明：检测到所有敌人被消灭后，可以调用enemies.RemoveAll(enemy => enemy == null)清理列表里的空引用，避免后续触发检测时重复遍历已销毁的无效元素，减少不必要的性能消耗。

内容的提问来源于stack exchange，提问作者Anthony Ruiz