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 0;
        }
    }

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 0;
        }
    }