1. 简介

定义
- 使用共享对象可有效地支持大量的细粒度的对象。

解决问题
- 面向对象技术可以很好地解决一些灵活性或可扩展性问题，但在很多情况下需要在系统中增加类和对象的个数。当对象数量太多时，将导致运行代价过高，带来性能下降等问题。享元模式正是为解决这一类问题而诞生的。

原理
- 享元模式其实就是工厂模式的一个改进机制，享元模式同样要求创建一个或一组对象，并且就是通过工厂方法生成对象的，只不过享元模式中为工厂方法增加了缓存这一功能。

类图

典型的例子，如：string对象，Type对象等，都是使用享元模式设计。

2. 示例

/// /// The 'Flyweight' class./// 
public class Character{    // intrinsic state    protected char _symbol;    protected int _size;    protected string _font;    // extrinsic state    protected Position _position;    public void Display(Position position)    {        Console.WriteLine(            String.Format("Symbol: {0} Size: {1} Font: {2} Position: {3} {4}",            _symbol, _size, _font, position._x, position._y));    }}/// /// A 'ConcreteFlyweight' class/// 
public class CharacterA : Character{    public CharacterA()    {        _symbol = 'A';        _size = 10;        _font = "宋体";        //_position = new Position(0, 1);    }}/// /// The 'FlyweightFactory' class/// 
public class CharacterFactory{    // Keeps the character object by specifying key/value.    private Dictionary
   
     _characters =        new Dictionary
    
     ();    public Character this[char key]    {        get        {            Character character = null;            // Checked the character whether existed or not,            // if the character existed, then directly returns,            // otherwise, instantiates a character object.            if (_characters.ContainsKey(key))            {                character = _characters[key];            }            else            {                string name = this.GetType().Namespace + "." +                              "Character" + key.ToString();                    character = Activator.CreateInstance(                        Type.GetType(name)) as Character;                _characters.Add(key, character);            }            return character;        }    }}/// 
     /// The client./// 
/// 
     The args.static void Main(string[] args){    string text = "ABZABBZZ";    char[] letters = text.ToCharArray();    var characterFactory = new CharacterFactory();    // Creates random position ranges 0 to 100.    var rd = new Random();    foreach (char c in letters)    {        Character character = characterFactory[c];        var p = new Position(rd.Next(0, 100), rd.Next(0, 100));        character.Display(p);    }    Console.ReadKey();}