为什么我的索引器不工作？

Question

Indexers allow instances of a class or struct to be indexed just like arrays. Indexers resemble properties except that their accessors take parameters.

我有这样的代码

class StudentMemento
    {
        Student student;
        public Student this[int index]
        {
            get { return student; }
            set { student = new Student { time = DateTime.Now }; }
        }
    }
    class Client
    {
        static void Main()
        {
            StudentMemento s = new StudentMemento();
            Student s1 = s[1];
            Student s2 = s[2];
            Student s3 = s[1];
            Console.Read();
        }
    }

根据 msdn 中的文档，我应该在以下成员 s1、s2 中获取 Student 的实例，因为我在 Indexer 中返回 Student 的对象，但我得到的是空引用。任何人都可以帮助我理解，为什么会这样。谢谢

Answer 1

之后

StudentMemento s = new StudentMemento();

s.student 将是 null。 student 字段仅在索引器 setter 中分配，因此您需要在调用 getter 之前调用它，例如

StudentMemento s = new StudentMemento();
s[1] = null;

Student s1 = s[1];
Student s2 = s[2];
Student s3 = s[1];

为什么我的索引器不工作？

Why my Indexer is not working?

c#

indexer