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

1. Override Equals, Get Hash Code, and the '==' Operator.

The Key class must override Equals in order for the Dictionary to detect if they are the same. The default implementation is going to check references only.

Here:

        public bool Equals(Key other)
        {
            return this == other;
        }

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

            return this.Equals((Key)obj);
        }

        public static bool operator ==(Key k1, Key k2)
        {
            if (object.ReferenceEquals(k1, k2))
            {
                return true;
            }

            if ((object)k1 == null || (object)k2 == null)
            {
                return false;
            }

            return k1.name == k2.name;
        }

        public static bool operator !=(Key k1, Key k2)
        {
            if (object.ReferenceEquals(k1, k2))
            {
                return false;
            }

            if ((object)k1 == null || (object)k2 == null)
            {
                return true;
            }

            return k1.name != k2.name;
        }

        public override int GetHashCode()
        {
            return this.name == null ? 0 : this.name.GetHashCode();
        }

2. If Possible, use a struct.

You should use a struct for immutable datatypes like this, since they are passed by value. This would mean that you coulnd't accidentally munge two different values into the same key.