/// <summary>
 /// 资源回收(卸载引用计数为零的资源)
 /// </summary>
 public static void UnloadUnusedAssets()
 {
     for (int i = _loaders.Count - 1; i >= 0; i--)
     {
         FileLoaderBase loader = _loaders[i];
         if (loader.CanDestroy())
         {
             loader.Destroy(true);
             _loaders.RemoveAt(i);
         }
     }
 }
 /// <summary>
 /// 实时销毁场景
 /// 注意:因为场景比较特殊,需要立刻回收
 /// </summary>
 private static void UpdateDestroyScene()
 {
     for (int i = _loaders.Count - 1; i >= 0; i--)
     {
         FileLoaderBase loader = _loaders[i];
         if (loader.IsSceneLoader && loader.CanDestroy())
         {
             loader.Destroy(true);
             _loaders.RemoveAt(i);
         }
     }
 }