Dictionary.ContainsKey return False, but a want True

Question

namespace Dic
{
public class Key
{
    string name;
    public Key(string n) { name = n; }
}

class Program
{
    static string Test()
    {
        Key a = new Key(         


        

Answer 1

Then you will need to override GetHashCode and Equals on the Key class.

Without doing that, you get the default implementation of both. Which results in the hashcode for a and b to be most likely not the same (I don't know how what the default implementation looks like), and a to be definitely not equal to b (the default Equals() implementation checks reference equality).

In your case, assuming "name" is not a null, it could be implemented as

   public class Key
   {
        string name;
        public override int GetHashCode()
        {
             return name.GetHashCode();
        }

        public override bool Equals(object obj)
        {
            if (obj == null)
            {
              return false;
            }

            Key objAsKey = obj as Key;
            if (objAsKey == null)
            {
              return false;
            }

            return this.name.Equals(objAsKey.Name);
        }
    }

Whether this is a satisfactory hash is a different story, but it shows the principle, nevertheless.