Overridding Equals和GetHash [英] Overridding Equals and GetHash

问题描述

我已阅读，当你重写equals上的类/对象则需要重写GetHashCode

I have read that when you override Equals on an class/object you need to override GetHashCode.

 public class Person : IEquatable<Person>
    {
        public int PersonId { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }

        public Person(int personId, string firstName, string lastName)
        {
            PersonId = personId;
            FirstName = firstName;
            LastName = lastName;

        }

        public bool Equals(Person obj)
        {
            Person p = obj as Person;

            if (ReferenceEquals(null, p)) 
                return false;
            if (ReferenceEquals(this, p)) 
                return true;

            return Equals(p.FirstName, FirstName) && 
                   Equals(p.LastName, LastName);
        }


    }

现在给出的以下内容：

 public static Dictionary<Person, Person> ObjDic= new Dictionary<Person, Person>();
 public static Dictionary<int, Person> PKDic = new Dictionary<int, Person>();

不会overridding的GetHashCode的影响两者的字典的上面？是怎么产生的GetHashCode什么，我基本上是问？如果我仍然期待在PKDic对象将我能够找到它只是基于PK的。如果我想重写的GetHashCode一个人如何会去这样做呢？

Will not overridding the GetHashCode affect both of the Dictionary's above? What I am basically asking is how is GetHashCode generated? IF I still look for an object in PKDic will I be able to find it just based of the PK. If I wanted to override the GetHashCode how would one go about doing that?

推荐答案

您应该的总是 。覆盖的GetHashCode

A 词典< INT，人> 将没有的GetHashCode ，但只要你调用LINQ方法，如鲜明或 GROUPBY ，它就会停止工作。

A Dictionary<int, Person> will function without GetHashCode, but as soon as you call LINQ methods like Distinct or GroupBy, it will stop working.

请注意，顺便说一句，你还没有真正覆盖等于无论是。
中的 IEquatable.Equals 方法是不一样的虚拟BOOL等于（obj对象）继承自对象。虽然默认的IEqualityComparer< T> 将使用 IEquatable< T>如果类实现它接口，你还是应该覆盖等于，因为其他代码可能不会。

Note, by the way, that you haven't actually overridden Equals either. The IEquatable.Equals method is not the same as the virtual bool Equals(object obj) inherited from Object. Although the default IEqualityComparer<T> will use the IEquatable<T> interface if the class implements it, you should still override Equals, because other code might not.

在你的情况，你应该重写等于和的GetHashCode 是这样的：

In your case, you should override Equals and GetHashCode like this:

public override bool Equals(object obj) { return Equals(obj as Person); }
public override int GetHashCode() {
    return FirstName.GetHashCode() ^ LastName.GetHashCode();
}

这篇关于Overridding Equals和GetHash的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！