索引
运用共享技术有效地支持大量细粒度的对象。
Use sharing to support large numbers of fine-grained objects efficiently.
下面的对象图说明了如何共享 Flyweight：
Flyweight
ConcreteFlyweight
UnsharedConcreteFlyweight
FlyweightFactory
Client
Flyweight 模式的有效性很大程度上取决于如何使用它以及在何处使用它。
当以下情况成立时可以使用 Flyweight 模式：
实现方式（一）：使用 FlyweightFactory 管理 Flyweight 对象。
Flyweight 模式的可用性在很大程度上取决于是否易识别外部状态并将它从共享对象中删除。
理想的状况是，外部状态可以由一个单独的对象结构计算得到，且该结构的存储要求非常小。
通常，因为 Flyweight 对象是共享的，用户不能直接对它进行实例化，因为 FlyweightFactory 可以帮助用户查找某个特定的 Flyweight 对象。
共享还意味着某种形式的引用计数和垃圾回收。
1 namespace FlyweightPattern.Implementation1 2 { 3 public abstract class Flyweight 4 { 5 public abstract string Identifier { get; } 6 public abstract void Operation(string extrinsicState); 7 } 8 9 public class ConcreteFlyweight : Flyweight 10 { 11 public override string Identifier 12 { 13 get { return "hello"; } 14 } 15 16 public override void Operation(string extrinsicState) 17 { 18 // do something 19 } 20 } 21 22 public class FlyweightFactory 23 { 24 private Dictionary<string, Flyweight> _pool 25 = new Dictionary<string, Flyweight>(); 26 27 public Flyweight CreateFlyweight(string identifier) 28 { 29 if (!_pool.ContainsKey(identifier)) 30 { 31 Flyweight flyweight = new ConcreteFlyweight(); 32 _pool.Add(flyweight.Identifier, flyweight); 33 } 34 35 return _pool[identifier]; 36 } 37 } 38 39 public class Client 40 { 41 public void TestCase1() 42 { 43 FlyweightFactory factory = new FlyweightFactory(); 44 Flyweight flyweight1 = factory.CreateFlyweight("hello"); 45 Flyweight flyweight2 = factory.CreateFlyweight("hello"); 46 flyweight1.Operation("extrinsic state"); 47 flyweight2.Operation("extrinsic state"); 48 } 49 } 50 }
设计模式之美：Flyweight（享元）,布布扣,bubuko.com
原文：http://www.cnblogs.com/gaochundong/p/design_pattern_flyweight.html