[原译]理解并实现原型模式-实现ICloneable接口.理解深浅拷贝
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本文用C#实现原型模式,也会讨论深浅拷贝,已经如何在.net中高效实现ICloneable 接口
介绍
有时候我们需要从上下文得到一个对象的拷贝，然后通过一些独立的操作来处理他。原型模式在这种情况下很适用
GoF 定义原型模式为用原型实例指定创建对象的种类，并且通过拷贝这些原型创建新的对象。
Specify the kind of objects to create using a prototypical instance, and create new objects by copying this prototype."
看一下类图
主要的参与者有
• Prototype: 抽象类或接口，定义了方法来拷贝自己
• ConcretePrototype: 克隆的具体类.
• Client: 需要执行拷贝对象的软件对象
然后实现吧
使用代码
为了简化。我以一个著名的偷车游戏作为例子
我们说游戏里有一个注脚。这个主要有着一些定义游戏数据的统计量。保存游戏的时候我们就需要拷贝这个对象，然后序列化到文件中。（仅仅是举个例子，真实的游戏里很少这样做）
下面这个类抽象类就是概念中的Prototype
public abstract class AProtagonist { int m_health; int m_felony; double m_money; public int Health { get { return m_health; } set { m_health = value; } } public int Felony { get { return m_felony; } set { m_felony = value; } } public double Money { get { return m_money; } set { m_money = value; } } public abstract AProtagonist Clone(); }
接口定义了玩家重要的信息，然后定义了一个Clone方法。然后我们定义一个具体的玩家类CJ。这样我们可以克隆当前对象，然后异步的进行序列化
class CJ : AProtagonist { public override AProtagonist Clone() { return this.MemberwiseClone() as AProtagonist; } }
这个类就是概念中的ConcretePrototype 。这里为了简化也没有其他一些方法了。
现在看看客户端软件的写法
static void Main(string[] args) { // 演示原型模式 CJ player = new CJ(); player.Health = 1; player.Felony = 10; player.Money = 2.0; Console.WriteLine("Original Player stats:"); Console.WriteLine("Health: {0}, Felony: {1}, Money: {2}", player.Health.ToString(), player.Felony.ToString(), player.Money.ToString()); // 这里是拷贝部分. CJ playerToSave = player.Clone() as CJ; Console.WriteLine("\nCopy of player to save on disk:"); Console.WriteLine("Health: {0}, Felony: {1}, Money: {2}", playerToSave.Health.ToString(), playerToSave.Felony.ToString(), playerToSave.Money.ToString()); }
理解深浅拷贝
上面的代码就模拟了原型模式，有一个问题就是我们使用了MemberwiseCopy 方法。而这个方法是创建浅拷贝的。如果对象里包含引用类型，引用类型的地址就会被从前者拷贝到后者。这样。两个就指向了同样的对象。
为了说明情况。我们让主角类包含更多的，叫做AdditionalDetails
public class AdditionalDetails { int m_charisma; int m_fitness; public int Charisma { get { return m_charisma; } set { m_charisma = value; } } public int Fitness { get { return m_fitness; } set { m_fitness = value; } } }
然后抽象类将会一个AdditionalDetails 对象
public abstract class AProtagonistEx { int m_health; int m_felony; double m_money; // 引用类型 AdditionalDetails m_details = new AdditionalDetails(); public int Health { get { return m_health; } set { m_health = value; } } public int Felony { get { return m_felony; } set { m_felony = value; } } public double Money { get { return m_money; } set { m_money = value; } } public AdditionalDetails Details { get { return m_details; } set { m_details = value; } } public abstract AProtagonistEx Clone(); }
具体类既然使用MemberwiseCopy实现拷贝
class CJEx : AProtagonistEx { public override AProtagonistEx Clone() { return this.MemberwiseClone() as AProtagonistEx; } } 问题来了。两份拷贝会指向同一个AdditionalDetials 对象 static void Main(string[] args) { // 演示浅拷贝 CJEx playerEx = new CJEx(); playerEx.Health = 1; playerEx.Felony = 10; playerEx.Money = 2.0; playerEx.Details.Fitness = 5; playerEx.Details.Charisma = 5; // 克隆对象然后改变引用类型的值 CJEx shallowClonedPlayer = playerEx.Clone() as CJEx; shallowClonedPlayer.Details.Charisma = 10; shallowClonedPlayer.Details.Fitness = 10; //看看发生了什么 Console.WriteLine("\nOriginal Object:"); Console.WriteLine("Charisma: {0}, Fitness: {1}", playerEx.Details.Charisma.ToString(), playerEx.Details.Fitness.ToString()); Console.WriteLine("\nShallow Cloned Object:"); Console.WriteLine("Charisma: {0}, Fitness: {1}", shallowClonedPlayer.Details.Charisma.ToString(), shallowClonedPlayer.Details.Fitness.ToString()); }
画个图。看得清楚些
为了避免这种期刊。我们需要在堆上创建引用类型的拷贝，然后对应赋值
class CJEx : AProtagonistEx { public override AProtagonistEx Clone() { CJEx cloned = this.MemberwiseClone() as CJEx; cloned.Details = new AdditionalDetails(); cloned.Details.Charisma = this.Details.Charisma; cloned.Details.Fitness = this.Details.Fitness; return cloned as AProtagonistEx; } }
这样就可以了
注意。当执行深拷贝的时候，可能引用类型来包括引用类型，因此好的做法是用反射。并且递归的拷贝。直到没有引用类型，具体可参考另一文
实现ICloneable接口
ICloneable接口提供了定义拷贝方法的接口。我们可以使用ICloneable 作为概念中的Prototype，我们看一下如果实现ConcretePrototype
public class CJFinal : ICloneable { int m_health; int m_felony; double m_money; AdditionalDetails m_details = new AdditionalDetails(); public int Health { get { return m_health; } set { m_health = value; } } public int Felony { get { return m_felony; } set { m_felony = value; } } public double Money { get { return m_money; } set { m_money = value; } } public AdditionalDetails Details { get { return m_details; } set { m_details = value; } } private object ShallowCopy() { return this.MemberwiseClone(); } private object DeepCopy() { CJFinal cloned = this.MemberwiseClone() as CJFinal; cloned.Details = new AdditionalDetails(); cloned.Details.Charisma = this.Details.Charisma; cloned.Details.Fitness = this.Details.Fitness; return cloned; } #region ICloneable Members public object Clone() { return DeepCopy(); } #endregion }
客户端代码如下
private static void ICloneableVersionCopy() { // 演示深拷贝 CJFinal player = new CJFinal(); player.Health = 1; player.Felony = 10; player.Money = 2.0; player.Details.Fitness = 5; player.Details.Charisma = 5; // 演示深拷贝 CJFinal clonedPlayer = player.Clone() as CJFinal; clonedPlayer.Details.Charisma = 10; clonedPlayer.Details.Fitness = 10; // 看看效果 Console.WriteLine("\nOriginal Object:"); Console.WriteLine("Charisma: {0}, Fitness: {1}", player.Details.Charisma.ToString(), player.Details.Fitness.ToString()); Console.WriteLine("\nICloneable Deep Cloned Object:"); Console.WriteLine("Charisma: {0}, Fitness: {1}", clonedPlayer.Details.Charisma.ToString(), clonedPlayer.Details.Fitness.ToString()); }
Demo下载
PrototypeDemo.zip
原文地址：Understanding-and-Implementing-Prototype-Pattern-i
著作权声明：本文由http://leaver.me 翻译，欢迎转载分享。请尊重作者劳动，转载时保留该声明和作者博客链接，谢谢！
