Question

我的班级：

public class myClass
{
    public int A { get; set; }
    public int B { get; set; }
    public int C { get; set; }
    public int D { get; set; }
}

和主要例子：

Dictionary<myClass, List<string>> dict = new Dictionary<myClass, List<string>>();
myClass first = new myClass();
first.A = 2;
first.B = 3;

myClass second = new myClass();
second.A = 2;
second.B = 3;
second.C = 5;
second.D = 6;

dict.Add(first, new List<string>());

if (dict.ContainsKey(second))
{
    //
    //should come here and update List<string> for first (and only in this example) key 
    //
}
else
{
    //
    //if myFirst object has difference vlues of A or B properties
    //
    dict.Add(second, new List<string>());
}

怎么做？

Answer 1

如果始终希望字典仅在A和B上进行比较，则有两种选择。要么use the constructor实现IEqualityComparer<TKey>并将比较逻辑放在那里，要么让你的类实现 ~~IEquateable<T>~~ GetHashCode和Equals 所以默认comparer会给你你想要的结果。

如果您只想在一种情况下比较A和B，则需要使用.Keys属性和允许您传入IEqualityComparer<T>的Linq扩展方法Contains。但是，当这样做时你会失去使用字典的速度优势，所以请谨慎使用它。

public class MyClassSpecialComparer : IEqualityComparer<myClass>
{
    public bool Equals (myClass x, myClass y)
    { 
        return x.A == y.A && x.B == y.B 
    }

    public int GetHashCode(myClass x)
    {
       return x.A.GetHashCode() + x.B.GetHashCode();
    }


}


 //Special case for when you only want it to compare this one time
 //NOTE: This will be much slower than a normal lookup.
    var myClassSpecialComparer = new MyClassSpecialComparer();
    Dictionary<myClass, List<string>> dict = new Dictionary<myClass, List<string>>();
    //(Snip)
    if (dict.Keys.Contains(second, myClassSpecialComparer ))
    {
        //
        //should come here and update List<string> for first (and only in this example) key 
        //
    }

 //If you want it to always compare
    Dictionary<myClass, List<string>> dict = new Dictionary<myClass, List<string>>(new MyClassSpecialComparer());

Answer 2

默认情况下，比较会根据哈希代码将对象放入存储区。如果两个哈希码相同，则执行详细比较（通过调用Equals）。如果您的类既不提供GetHashCode也不实现相等，则将使用默认的object.GetHashCode - 在这种情况下，您的类的任何特定内容都不会用于值比较语义。只会找到相同的参考。如果您不想这样做，请实现GetHashCode并实现相等。

例如：

public class myClass
{
    public int A { get; set; }
    public int B { get; set; }
    public int C { get; set; }
    public int D { get; set; }

    public bool Equals(myClass other)
    {
        if (ReferenceEquals(null, other)) return false;
        if (ReferenceEquals(this, other)) return true;
        return other.A == A && other.B == B && other.C == C && other.D == D;
    }

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

    public override int GetHashCode()
    {
        unchecked
        {
            int result = A;
            result = (result*397) ^ B;
            result = (result*397) ^ C;
            result = (result*397) ^ D;
            return result;
        }
    }
}

Answer 3

在myClass中覆盖：

GetHashCode方法
等于方法

要实现GetHashCode方法，您只需从整数属性中XOR GetHashCodes。

可选择覆盖ToString方法并实现IEquatable接口

比较在Dictionary中用作Key的对象

3 个答案: