public class Product

{

    /// <summary>

    /// 自增ID

    /// </summary>

    public int ID { get; set; }

    /// <summary>

    /// 主键

    /// </summary>

    public string Code { get; set; }

    /// <summary>

    /// 名称

    /// </summary>

    public string Name { get; set; }

    /// <summary>

    /// 类型

    /// </summary>

    public string Category { get; set; }

    /// <summary>

    /// 价格

    /// </summary>

    public decimal Price { get; set; }

    /// <summary>

    /// 生产日期

    /// </summary>

    public DateTime ProduceDate { get; set; }

    public override string ToString()

    {

        return string.Format("{0}{1}{2}{3}{4}{5}", ID.ToString().PadLeft(), Category.PadLeft(), Code.PadLeft(), Name.PadLeft(), Price.ToString().PadLeft(), ProduceDate.ToString("yyyy-M-d").PadLeft());

    }

    public static ProductCollection GetSampleCollection()

    {

        ProductCollection collection = new ProductCollection(

            new Product() { ID = , Code = "", Category = "Red Wine", Name = "Product1" }

            , new Product() { ID = , Code = "", Category = "Red Wine", Name = "Product2" }

            , new Product() { ID = , Code = "", Category = "Red Wine", Name = "Product3" }

            , new Product() { ID = , Code = "", Category = "Red Wine", Name = "Product4" }

            , new Product() { ID = , Code = "", Category = "Red Wine", Name = "Product5" }

            , new Product() { ID = , Code = "", Category = "Red Wine", Name = "Product6" }

            , new Product() { ID = , Code = "", Category = "Red Wine", Name = "Product7" }

        );

        return collection;

    }

}

public class ProductCollection : IEnumerable<Product>

{

    private List<Product> list = new List<Product>();

    private Hashtable table;

    public ProductCollection()

    {

        table = new Hashtable();

    }

    public ProductCollection(params Product[] array)

    {

        table = new Hashtable();

        foreach (Product item in array)

        {

            this.Add(item);

        }

    }

    public ICollection Keys

    {

        get { return table.Keys; }

    }

    private string getKey(int index)

    {

        if (index <  || index > table.Keys.Count) throw new Exception("索引超出了范围");

        string selected = "";

        int i = ;

        foreach (string key in table.Keys)

        {

            if (i == index)

            {

                selected = key; break;

            }

            i++;

        }

        return selected;

    }

    /// <summary>

    /// 索引器 支持类似于collection[index]这样的访问

    /// </summary>

    /// <param name="index"></param>

    /// <returns></returns>

    public Product this[int index]

    {

        get { string key = getKey(index); return table[key] as Product; }

        set { string key = getKey(index); table[key] = value; }

    }

    private string getKey(string key)

    {

        foreach (string k in table.Keys)

        {

            if (key == k)

            {

                return key;

            }

        }

        throw new Exception("不存在此键值");

    }

    /// <summary>

    /// 索引器 类似于collection[key]这样的访问

    /// </summary>

    /// <param name="key"></param>

    /// <returns></returns>

    public Product this[string key]

    {

        get { string selected = getKey(key); return table[selected] as Product; }

        set { string selected = getKey(key); table.Remove(table[selected]); this.Add(value); }

    }

    /// <summary>

    /// 在末尾添加成员

    /// </summary>

    /// <param name="item"></param>

    public void Add(Product item)

    {

        //确保key不重复

        foreach (string key in table.Keys)

        {

            if (key == item.Code) throw new Exception("产品代码不能重复");

        }

        table.Add(item.Code, item);

    }

    /// <summary>

    /// 在任意位置添加成员

    /// </summary>

    /// <param name="index"></param>

    /// <param name="item"></param>

    public void Insert(int index, Product item) { }

    /// <summary>

    /// 移除某一成员

    /// </summary>

    /// <param name="item"></param>

    /// <returns></returns>

    public bool Remove(Product item)

    {

        return true;

    }

    /// <summary>

    /// 移除某一位置的成员

    /// </summary>

    /// <param name="index"></param>

    /// <returns></returns>

    public bool RemoveAt(int index) { return true; }

    /// <summary>

    /// 清除所有成员

    /// </summary>

    public void Clear() { table.Clear(); }

    public IEnumerator<Product> GetEnumerator()

    {

        return new ProductEnumerator(this);

    }

    IEnumerator IEnumerable.GetEnumerator()

    {

        return new ProductEnumerator(this);

    }

    /// <summary>

    /// 获得集合的成员数量

    /// </summary>

    public int Count { get { return table.Keys.Count; } }

    public class ProductEnumerator : IEnumerator<Product>

    {

        private ProductCollection collection;

        private int index;

        public ProductEnumerator(ProductCollection productCollection)

        {

            this.collection = productCollection;

            index = -;

        }

        public Product Current { get { return collection[index]; } }

        object IEnumerator.Current { get { return collection[index]; } }

        public void Dispose() { }

        public bool MoveNext()

        {

            index++;

            if (index >= collection.Count) return false;

            else return true;

        }

        public void Reset() { index = -; }

    }

}

ProductCollection pc = Product.GetSampleCollection();

//for (int i = 0; i < pc.Count-1; i++)

//{

//    string line = pc[i].ToString();

//    Console.WriteLine(line);

//}

foreach (string item in pc.Keys)

{

    Console.WriteLine(pc[item]);

}

Console.ReadKey();