Question

我有一个案例，我需要抓取一堆不同的项目，但我的源是一个具有两个属性的对象的集合，如下所示：

public class SkillRequirement
{
    public string Skill { get; set; }
    public string Requirement { get; set; }
}

我尝试按如下方式获取一个集合：

SkillRequirementComparer sCom = new SkillRequirementComparer();

var distinct_list = source.Distinct(sCom);

我尝试为此实现IEqualityComparer<T>，但我对GetHashCode()方法感到难过。

Comparer的类：

public class SkillRequirementComparer : IEqualityComparer<SkillRequirement>
{
    public bool Equals(SkillRequirement x, SkillRequirement y)
    {
        if (x.Skill.Equals(y.Skill) && x.Requirement.Equals(y.Requirement))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(SkillRequirement obj)
    {
        //?????
    }
}

通常我会在属性上使用GetHashCode()，但因为我在两个属性上进行比较，所以我有点不知所措。我做错了什么，或者遗漏了一些非常明显的东西？

Answer 1

您可以通过以下方式实施GetHashCode：

public int GetHashCode(SkillRequirement obj)
{
    unchecked
    {
        int hash = 17;
        hash = hash * 23 + obj.Skill.GetHashCode();
        hash = hash * 23 + obj.Requirement.GetHashCode();
        return hash;
    }
}

来自J.Skeet的_originally

如果属性可以是null，则应避免使用NullReferenceException，例如：

int hash = 17;
hash = hash * 23 + (obj.Skill ?? "").GetHashCode();
hash = hash * 23 + (obj.Requirement ?? "").GetHashCode();
return hash;

Answer 2

我想链接下面的堆栈溢出帖子，虽然问题已经回答了。

GetHashCode -

Why is it important to override GetHashCode when Equals method is overridden?

另外，在上面的回答中，Tim Schmelter说the properties can be null you should avoid a NullReferenceException

int hash = 17;
hash = hash * 23 + (obj.Skill ?? "").GetHashCode();
hash = hash * 23 + (obj.Requirement ?? "").GetHashCode();
return hash;

IEqualityComparer -

What is the difference between using IEqualityComparer and Equals/GethashCode Override
What's the role of GetHashCode in the IEqualityComparer in .NET?
How and when to use IEqualityComparer in C#

IEquatable - What's the difference between IEquatable and just overriding Object.Equals()?

等于 - Guidelines for Overloading Equals()

class TwoDPoint : System.Object
{
    public readonly int x, y;

    public TwoDPoint(int x, int y)  //constructor
    {
        this.x = x;
        this.y = y;
    }

    public override bool Equals(System.Object obj)
    {
        // If parameter is null return false.
        if (obj == null)
        {
            return false;
        }

        // If parameter cannot be cast to Point return false.
        TwoDPoint p = obj as TwoDPoint;
        if ((System.Object)p == null)
        {
            return false;
        }

        // Return true if the fields match:
        return (x == p.x) && (y == p.y);
    }

    public bool Equals(TwoDPoint p)
    {
        // If parameter is null return false:
        if ((object)p == null)
        {
            return false;
        }

        // Return true if the fields match:
        return (x == p.x) && (y == p.y);
    }

    public override int GetHashCode()
    {
        //return x ^ y;
    }
}

在具有C＃</t>中两个属性的对象上实现IEqualityComparer <t>

2 个答案: