创建型设计模式之工厂模式(Abstract Factory)

结构

意图	提供一个创建一系列相关或相互依赖对象的接口，而无需指定它们具体的类。

适用性	一个系统要独立于它的产品的创建、组合和表示时。 一个系统要由多个产品系列中的一个来配置时。 当你要强调一系列相关的产品对象的设计以便进行联合使用时。 当你提供一个产品类库，而只想显示它们的接口而不是实现时。

 using System;

     // These classes could be part of a framework,
     // which we will call DP
     // ===========================================

     abstract class DPDocument
     {
         abstract public void Dump();
     }

     abstract class DPWorkspace
     {
         abstract public void Dump();
     }

     abstract class DPView
     {
         abstract public void Dump();
     }    

     abstract class DPFactory
     {
         abstract public DPDocument CreateDocument();
         abstract public DPView CreateView();
         abstract public DPWorkspace CreateWorkspace();
     }

     abstract class DPApplication
     {
         protected DPDocument doc;
         protected DPWorkspace workspace;
         protected DPView view;

         public void ConstructObjects(DPFactory factory)
         {
             // Create objects as needed
             doc = factory.CreateDocument();
             workspace = factory.CreateWorkspace();
             view = factory.CreateView();
         }        

         abstract public void Dump();

         public void DumpState()
         {
             if (doc != null) doc.Dump();
             if (workspace != null) workspace.Dump();
             if (view != null) view.Dump();
         }
     }

     // These classes could be part of an application
     class MyApplication : DPApplication
     {
         MyFactory myFactory = new MyFactory();

         override public void Dump()
         {
             Console.WriteLine("MyApplication exists");
         }

         public void CreateFamily()
         {
             MyFactory myFactory = new MyFactory();
             ConstructObjects(myFactory);
         }
     }    

     class MyDocument : DPDocument
     {
         public MyDocument()
         {
                 Console.WriteLine("in MyDocument constructor");
         }

         override public void Dump()
         {
             Console.WriteLine("MyDocument exists");
         }
     }

     class MyWorkspace : DPWorkspace
     {
         override public void Dump()
         {
             Console.WriteLine("MyWorkspace exists");
         }
     }

     class MyView : DPView
     {
         override public void Dump()
         {
             Console.WriteLine("MyView exists");
         }
     }

     class MyFactory : DPFactory
     {
         override public DPDocument CreateDocument()
         {
             return new MyDocument();
         }
         override public DPWorkspace CreateWorkspace()
         {
             return new MyWorkspace();
         }
         override public DPView CreateView()
         {
             return new MyView();
         }
     }

     /// <summary>
     ///    Summary description for Client.
     /// </summary>
     public class Client
     {
         public static int Main(string[] args)
         {
             MyApplication myApplication = new MyApplication();

             myApplication.CreateFamily();

             myApplication.DumpState();

             return ;
         }
     }

工厂模式

名称	Factory Method
结构
意图	定义一个用于创建对象的接口，让子类决定实例化哪一个类。Factory Method 使一个类的实例化延迟到其子类。
适用性	当一个类不知道它所必须创建的对象的类的时候。 当一个类希望由它的子类来指定它所创建的对象的时候。 当类将创建对象的职责委托给多个帮助子类中的某一个，并且你希望将哪一个帮助子类是代理者这一信息局部化的时候。

 using System;

     // These two classes could be part of a framework,
     // which we will call DP
     // ===============================================

     class DPDocument
     {

     }

     abstract class DPApplication
     {
         protected DPDocument doc;

         abstract public void CreateDocument();

         public void ConstructObjects()
         {

             // Create objects as needed
             // . . .

             // including document
             CreateDocument();
         }
         abstract public void Dump();
     }

     // These two classes could be part of an application
     // =================================================

     class MyApplication : DPApplication
     {
         override public void CreateDocument()
         {
             doc = new MyDocument();
         }            

         override public void Dump()
         {
             Console.WriteLine("MyApplication exists");
         }
     }    

     class MyDocument : DPDocument
     {

     }

     /// <summary>
     ///    Summary description for Client.
     /// </summary>
     public class Client
     {
         public static int Main(string[] args)
         {
             MyApplication myApplication = new MyApplication();

             myApplication.ConstructObjects();

             myApplication.Dump();

             return ;
         }
     }

工厂方法