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 |
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example
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// Factory Method
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// Intent: "Define an interface for creating an object, but let subclasses
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// decide which class to instantiate. Factory Method lets a class defer
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// instantiation to subclasses".
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// For further information, read "Design Patterns", p107, Gamma et al.,
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// Addison-Wesley, ISBN:0-201-63361-2
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/* Notes:
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* This design pattern is often used in a framework architecture, which
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* contains a number of related classes inside the framework, and which
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* expects application developers to derive custom classes from them.
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* If the instantiation of some custom application classes needs to be
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* carried out inside framework code, then the Factory Method design
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* pattern is an ideal solution.
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*
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* The sample below is based on a document view architecture.
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* It shows the framework providing classes DPApplication and DPDocument
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* and the application providing MyApplication and MyDocument, derived
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* from the corresponding framework classes. Note how the construction
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* of MyDocument is initiated from inside the framework's DPApplication,
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* yet the framework was not written specifically for it.
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*
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* It could be extended for views and workspaces along the same lines.
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*/
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namespace FactoryMethod_DesignPattern
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{
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using System;
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// These two classes could be part of a framework,
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// which we will call DP
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// ===============================================
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class DPDocument
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{
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}
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abstract class DPApplication
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{
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protected DPDocument doc;
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abstract public void CreateDocument();
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public void ConstructObjects()
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{
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// Create objects as needed
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// . . .
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// including document
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CreateDocument();
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}
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abstract public void Dump();
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}
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// These two classes could be part of an application
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// =================================================
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class MyApplication : DPApplication
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{
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override public void CreateDocument()
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{
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doc = new MyDocument();
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}
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override public void Dump()
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{
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Console.WriteLine("MyApplication exists");
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}
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}
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class MyDocument : DPDocument
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{
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}
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/// <summary>
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/// Summary description for Client.
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/// </summary>
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public class Client
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{
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public static int Main(string[] args)
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{
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MyApplication myApplication = new MyApplication();
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myApplication.ConstructObjects();
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myApplication.Dump();
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return 0;
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}
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}
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