c# IDictionary接口的应用

using  System;
using  System.Collections.Generic;
using  System.Collections;
using  System.Text;

namespace  fanxing
... {

    public class SimpleDictionary : IDictionary
    ...{
        private DictionaryEntry[] items;
        private Int32 ItemsInUse = 0;

        public SimpleDictionary(Int32 numItems)
        ...{
            items = new DictionaryEntry[numItems];
        }

        public bool IsReadOnly ...{ get ...{ return false; } }
        public bool Contains(object key)
        ...{
            Int32 index;
            return TryGetIndexOfKey(key, out index);
        }
        public bool IsFixedSize ...{ get ...{ return false; } }
        public void Remove(object key)
        ...{
            if (key == null) throw new ArgumentNullException("key");
            Int32 index;
            if (TryGetIndexOfKey(key, out index))
            ...{
                Array.Copy(items, index + 1, items, index, ItemsInUse - index - 1);
                ItemsInUse--;
            }
            else
            ...{

            }
        }
        public void Clear()
        ...{
            if(ItemsInUse!=0)
            ...{
                for (int i = 0; i < ItemsInUse;i++ )
                ...{
                    items[i].Key = null;
                    items[9].Value = null;
                }
            }
            ItemsInUse = 0; 
        }
        public void Add(object key, object value)
        ...{
            try
            ...{
                if (ItemsInUse == items.Length)
                    throw new InvalidOperationException("The dictionary cannot hold any more items.");
                items[ItemsInUse++] = new DictionaryEntry(key, value);
            }
            catch (Exception e)
            ...{
                Console.Write(e.Message);
            }
        }
        public ICollection Keys
        ...{
            get
            ...{
                Object[] keys = new Object[ItemsInUse];
                for (Int32 n = 0; n < ItemsInUse; n++)
                    keys[n] = items[n].Key;
                return keys;
            }
        }
        public ICollection Values
        ...{
            get
            ...{
                Object[] values = new Object[ItemsInUse];
                for (Int32 n = 0; n < ItemsInUse; n++)
                    values[n] = items[n].Value;
                return values;
            }
        }
        public object this[object key]
        ...{
            get
            ...{
                Int32 index;
                if (TryGetIndexOfKey(key, out index))
                ...{
                    return items[index].Value;
                }
                else
                ...{
                    return null;
                }
            }

            set
            ...{
                Int32 index;
                if (TryGetIndexOfKey(key, out index))
                ...{
                    items[index].Value = value;
                }
                else
                ...{
                    Add(key, value);
                }
            }
        }
        private Boolean TryGetIndexOfKey(Object key, out Int32 index)
        ...{
            for (index = 0; index < ItemsInUse; index++)
            ...{
                if (items[index].Key.Equals(key)) return true;
            }
            return false;
        }
        private class SimpleDictionaryEnumerator : IDictionaryEnumerator
        ...{
            DictionaryEntry[] items;
            Int32 index = -1;

            public SimpleDictionaryEnumerator(SimpleDictionary sd)
            ...{
                items = new DictionaryEntry[sd.Count];
                Array.Copy(sd.items, 0, items, 0, sd.Count);
            }

            public Object Current ...{ get ...{ ValidateIndex(); return items[index]; } }

            public DictionaryEntry Entry
            ...{
                get ...{ return (DictionaryEntry)Current; }
            }

            public Object Key ...{ get ...{ ValidateIndex(); return items[index].Key; } }

            public Object Value ...{ get ...{ ValidateIndex(); return items[index].Value; } }

            public Boolean MoveNext()
            ...{
                if (index < items.Length - 1) ...{ index++; return true; }
                return false;
            }

            private void ValidateIndex()
            ...{
                if (index < 0 || index >= items.Length)
                    throw new InvalidOperationException("Enumerator is before or after the collection.");
            }

            public void Reset()
            ...{
                index = -1;
            }
        }
        public IDictionaryEnumerator GetEnumerator()
        ...{
            return new SimpleDictionaryEnumerator(this);//这里需要注意，返回的是一个接口，那我们new的类即 SimpleDictionaryEnumerator就必须要继承该接口，从而返回的该对象 new SimpleDictionaryEnumerator(this)实例只能用 IDictionaryEnumerator 接口下定义的方法。
        }

        public bool IsSynchronized ...{ get ...{ return false; } }
        public object SyncRoot ...{ get ...{ throw new NotImplementedException(); } }
        public int Count ...{ get ...{ return ItemsInUse; } }
        public void CopyTo(Array array, int index) ...{ throw new NotImplementedException(); }

        IEnumerator IEnumerable.GetEnumerator()
        ...{
            return ((IDictionary)this).GetEnumerator();
        }

       class Application7
       ...{

          static void Main(string[] args)
           ...{
               SimpleDictionary aa = new SimpleDictionary(2);
               aa.Add("a", "aaa");
               aa.Add("b", "aaa");
               Console.Write(aa.Keys.Count+"===="+aa.Values.Count);
               IEnumerable bb = aa;
               bb.GetEnumerator();
              foreach(DictionaryEntry cc in aa)
              ...{
                 Console.Write(cc.Key);
              }
               Console.Read();
           }
       }
    }
}

 
这是我抄自msdn的例子：
IDictionary接口是hashtable实现的重要接口，对于复杂的hashtable大家可能感觉过于麻烦，东西太多，一头雾水，因为hashtable里面有许多东西实现起来却是麻烦，许多数据结构的知识在里面，容易让人郁闷。但是看了 SimpleDictionary 这个类的实现，大家就可以对hashtable的实现有了大体甚至是全局的了解，看了以后会让你
茅塞顿开的，里面有些小细节与微软的方法还是有出入，实现一个方法有很多种，只要实现即可。