讲解C#设计模式编程中享元模式的运用

/// <summary>
 /// 客户端调用
 /// </summary>
 class Client
 {
  static void Main(string[] args)
  {
   // 定义外部状态，例如字母的位置等信息
   int externalstate = 10;
   // 初始化享元工厂
   FlyweightFactory factory = new FlyweightFactory();
   // 判断是否已经创建了字母A，如果已经创建就直接使用创建的对象A
   Flyweight fa = factory.GetFlyweight("A");
   if (fa != null)
   {
    // 把外部状态作为享元对象的方法调用参数
    fa.Operation(--externalstate);
   }
   // 判断是否已经创建了字母B
   Flyweight fb = factory.GetFlyweight("B");
   if (fb != null)
   {
    fb.Operation(--externalstate);
   }
   // 判断是否已经创建了字母C
   Flyweight fc = factory.GetFlyweight("C");
   if (fc != null)
   {
    fc.Operation(--externalstate);
   }
   // 判断是否已经创建了字母D
   Flyweight fd= factory.GetFlyweight("D");
   if (fd != null)
   {
    fd.Operation(--externalstate);
   }
   else
   {
    Console.WriteLine("驻留池中不存在字符串D");
    // 这时候就需要创建一个对象并放入驻留池中
    ConcreteFlyweight d = new ConcreteFlyweight("D");
    factory.flyweights.Add("D", d);
   }
   Console.Read();
  }
 }
 /// <summary>
 /// 享元工厂，负责创建和管理享元对象
 /// </summary>
 public class FlyweightFactory
 {
  // 最好使用泛型Dictionary<string,Flyweighy>
  //public Dictionary<string, Flyweight> flyweights = new Dictionary<string, Flyweight>();
  public Hashtable flyweights = new Hashtable();
  public FlyweightFactory()
  {
   flyweights.Add("A", new ConcreteFlyweight("A"));
   flyweights.Add("B", new ConcreteFlyweight("B"));
   flyweights.Add("C", new ConcreteFlyweight("C"));
  }
  public Flyweight GetFlyweight(string key)
  {
// 更好的实现如下
   //Flyweight flyweight = flyweights[key] as Flyweight;
   //if (flyweight == null)
   //{
   // Console.WriteLine("驻留池中不存在字符串" + key);
   // flyweight = new ConcreteFlyweight(key);
   //}
   //return flyweight;
return flyweights[key] as Flyweight;
  }
 }
 /// <summary>
 /// 抽象享元类，提供具体享元类具有的方法
 /// </summary>
 public abstract class Flyweight
 {
  public abstract void Operation(int extrinsicstate);
 }
 // 具体的享元对象，这样我们不把每个字母设计成一个单独的类了，而是作为把共享的字母作为享元对象的内部状态
 public class ConcreteFlyweight : Flyweight
 {
  // 内部状态
  private string intrinsicstate ;
  // 构造函数
  public ConcreteFlyweight(string innerState)
  {
   this.intrinsicstate = innerState;
  }
  /// <summary>
  /// 享元类的实例方法
  /// </summary>
  /// <param name="extrinsicstate">外部状态</param>
  public override void Operation(int extrinsicstate)
  {
   Console.WriteLine("具体实现类: intrinsicstate {0}, extrinsicstate {1}", intrinsicstate, extrinsicstate);
  }
 }