C# Generic Dictionary TryGetValue doesn't find keys

Question

I have this simple example:

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;
        }
    }
}

This is working fine. But if I change the MyKey struct by a MyKey class in this way:

public class MyKey

Then method TryGetValue doesn't find any key in spite of the key is out there.

I am sure I am missing something obvious but I don't know what.

Any idea ?

Thanks

---

** Solution **

(please, see accepted solution for better GetHashCode resolution)

I have redefined MyKey class like this, and all is working fine now:

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();
    }    
}

Thanks to all people answered this.

Answer 1

You need to override Equals() and GetHashCode() in the class MyKey

Maybe something like this:

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;
    }
}

Equals

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);
}