C#设计模式之Factory Method

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 :

1. 当一个类不知道它所必须创建的对象的类的时候。
2. 当一个类希望由它的子类来指定它所创建的对象的时候。
3. 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。

示例代码：

// Factory Method
namespace FactoryMethod_DesignPattern
{
    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 description for Client.
    ///

    public class Client
    {
        public static int Main(string[] args)
        {
            MyApplication myApplication = new MyApplication();

            myApplication.ConstructObjects();

            myApplication.Dump();
            
            return 0;
        }
    }
}