c# – 如何返回可为空的结构？

我有一个方法,我想返回PrefabItem或null.但是,当我执行以下操作时,出现错误：

Cannot convert null to ‘PrefabItem’ because it is a non-nullable value type

struct PrefabItem { }

public class A {
  int prefabSelected = -1;
  private static List<PrefabItem> prefabs = new List<PrefabItem>();

  private PrefabItem GetPrefabItem() {
    if (prefabSelected > -1) {
      return prefabs[prefabSelected];
    }
    return null;
  }
}

我看到我可以使用Nulllable< T>,但是当我这样做时,我收到相同的消息.

struct PrefabItem { }

struct Nullable<T> {
  public bool HasValue;
  public T Value;
}

public class A {
  int prefabSelected = -1;
  private static Nullable<List<PrefabItem>> prefabs = new Nullable<List<PrefabItem>>();

  private PrefabItem GetPrefabItem() {
    if (prefabSelected > -1) {
      return prefabs.Value[prefabSelected];
    }
    return null;
  }
}

我需要做什么才能让我的方法返回PrefabItem或null？

你应该返回Nullable< PrefabItem>还是PrefabItem？

无效语法示例：

private PrefabItem? GetPrefabItem() {
    if (prefabSelected > -1) {
      return prefabs[prefabSelected];
    }
    return null;
  }

还有一条评论.如果您需要无效元素列表,则列表的声明应该是：

private static List<PrefabItem?> prefabs = new List<PrefabItem?>();

要么

private static List<Nullable<PrefabItem>> prefabs = new List<Nullable<PrefabItem>>();