一个非常有用的关于集合的例子，实现集合的add,remove和this[index]方法

Animals.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DictionaryAnimals
{
   public class Animals : DictionaryBase
   {
      public void Add(string newID, Animal newAnimal)
      {
         Dictionary.Add(newID, newAnimal);
      }

      public void Remove(string animalID)
      {
         Dictionary.Remove(animalID);
      }

      public new IEnumerator GetEnumerator()
      {
         foreach (object animal in Dictionary.Values)
            yield return (Animal)animal;
      }

      public Animal this[string animalID]
      {
         get
         {
            return (Animal)Dictionary[animalID];
         }
         set
         {
            Dictionary[animalID] = value;
         }
      }
   }

}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DictionaryAnimals
{
   class Program
   {
      static void Main(string[] args)
      {
         Animals animalCollection = new Animals();
         animalCollection.Add("Jack", new Cow("Jack"));
         animalCollection.Add("Vera", new Chicken("Vera"));
         foreach (Animal myAnimal in animalCollection)
         {
            Console.WriteLine("New {0} object added to custom collection, " +
                              "Name = {1}", myAnimal.ToString(), myAnimal.Name);
         }
         Console.ReadKey();
      }
   }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DictionaryAnimals
{
   public abstract class Animal
   {
      protected string name;

      public string Name
      {
         get
         {
            return name;
         }
         set
         {
            name = value;
         }
      }

      public Animal()
      {
         name = "The animal with no name";
      }

      public Animal(string newName)
      {
         name = newName;
      }

      public void Feed()
      {
         Console.WriteLine("{0} has been fed.", name);
      }
   }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DictionaryAnimals
{
   public class Chicken : Animal
   {
      public void LayEgg()
      {
         Console.WriteLine("{0} has laid an egg.", name);
      }

      public Chicken(string newName) : base(newName)
      {
      }
   }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DictionaryAnimals
{
   public class Cow : Animal
   {
      public void Milk()
      {
         Console.WriteLine("{0} has been milked.", name);
      }

      public Cow(string newName) : base(newName)
      {
      }
   }
}