如何更改哈希码？

Question

我有一个 class 创建对象：

public class Creator
{
    public void DoSomething()
    {
        //I need to change the field of the Dog class here  
    }

    public Dog Create()
    {
        return new Dog("Buddy", new DateTime(2000, 9, 29));
    }
}

和class狗：

    public class Dog
    {
        public string Name { get; private set; }
        public DateTime BirthDate { get; private set; }

        public Dog(string name, DateTime birthDate)
        {
            Name = name;
            BirthDate = birthdate;
        }

        protected bool Equals(Dog other)
        {
            return Name.Equals(other.Name) 
                    && BirthDate.Equals(other.BirthDate);
        }

        public override bool Equals(object obj)
        {
            if (ReferenceEquals(null, obj)) return false;
            if (ReferenceEquals(this, obj)) return true;
            if (obj.GetType() != this.GetType()) return false;
            return Equals((Dog) obj);
        }

        public override int GetHashCode()
        {
            return unchecked(Name.GetHashCode()*397 
                             ^ BirthDate.GetHashCode());
        }

        public void ChangeName(string name)
        {
            Name = name;
        }
    }
}

然后，在另一个 class 中，我在哈希集中添加创建的 Dog 对象。我需要通过从 Creator class 更改 Dog class 的对象来使 hashset 停止正常工作。我该怎么做？

Answer 1

您的对象不是不可变的，您将其用作 HashSet<> 的 "key"...这是自找麻烦...

Dog dog = Create();
HashSet<Dog> dogs = new HashSet<Dog>();

dogs.Add(dog);
Console.WriteLine(dogs.Contains(dog)); // True

dog.ChangeName("Foo");
Console.WriteLine(dogs.Contains(dog)); // False

如果您更改其中一个属性，GetHashCode() 是根据在将对象插入 HashSet<> 之后计算得出的，您将 "break" HashSet<>.

如何更改哈希码？

How to change the hashcode?

c#

hashset

gethashcode