C# 通用字典 TryGetValue 找不到键

Question

我有这个简单的例子:

using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Dictionary<MyKey, string> data = new Dictionary<MyKey, string>();
            data.Add(new MyKey("1", "A"), "value 1A");
            data.Add(new MyKey("2", "A"), "value 2A");
            data.Add(new MyKey("1", "Z"), "value 1Z");
            data.Add(new MyKey("3", "A"), "value 3A");

            string myValue;
            if (data.TryGetValue(new MyKey("1", "A"), out myValue))
                Console.WriteLine("I have found it: {0}", myValue );

        }
    }

    public struct MyKey
    {
        private string row;
        private string col;

        public string Row { get { return row; } set { row = value; } }
        public string Column { get { return col; } set { col = value; } }

        public MyKey(string r, string c)
        {
            row = r;
            col = c;
        }
    }
}

这工作正常。但是，如果我以这种方式通过 MyKey 类更改 MyKey 结构:

public class MyKey

然后方法 TryGetValue 没有找到任何 key ，尽管 key 就在那里。

我确信我遗漏了一些明显的东西，但我不知道是什么。

有什么想法吗？

谢谢

---

** 解决方案 **

(请参阅接受的解决方案以获得更好的 GetHashCode 解析)

我已经像这样重新定义了 MyKey 类，现在一切正常:

public class MyKey
{
    private string row;
    private string col;

    public string Row { get { return row; } set { row = value; } }
    public string Column { get { return col; } set { col = value; } }

    public MyKey(string r, string c)
    {
        row = r;
        col = c;
    }

    public override bool Equals(object obj)
    {
        if (obj == null || !(obj is MyKey)) return false;

        return ((MyKey)obj).Row == this.Row && ((MyKey)obj).Column == this.Column;
    }

    public override int GetHashCode()
    {            
        return (this.Row + this.Column).GetHashCode();
    }    
}

感谢所有回答此问题的人。

Answer 1

您需要重写 MyKey 类中的 Equals() 和 GetHashCode()

也许是这样的:

GetHashCode()

public override int GetHashCode()
{
   return GetHashCodeInternal(Row.GetHashCode(),Column.GetHashCode());
}
//this function should be move so you can reuse it
private static int GetHashCodeInternal(int key1, int key2)
{
    unchecked
    {
        //Seed
        var num = 0x7e53a269;

        //Key 1
        num = (-1521134295 * num) + key1;
        num += (num << 10);
        num ^= (num >> 6);

        //Key 2
        num = ((-1521134295 * num) + key2);
        num += (num << 10);
        num ^= (num >> 6);

        return num;
    }
}

等于

public override bool Equals(object obj)
{
    if (obj == null)
        return false;
    MyKey p = obj as MyKey;
    if (p == null)
        return false;

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