.NET 代理(Proxy)模式

目录

1. 定义
2. UML
3. 参与者
4. 示例

定义：

代理模式给某一个对象提供一个代理对象，并由代理对象控制对原对象的引用。

UML:

参与者：

抽象主题(Subject)角色:

声明了代理主题和真实主题的公共接口,使任何需要真实主题的地方都能用代理主题代替.

具体主题(RealSubject)角色：

实现抽象主题角色的具体对象。

代理主题(Proxy)角色:

含有真实主题的引用,从而可以在任何时候操作真实主题,代理主题功过提供和真实主题相同的接口,使它可以随时代替真实主题.代理主题通过持有真实主题的引用,不但可以控制真实主题的创建或删除,可以在真实主题被调用前进行拦截,或在调用后进行某些操作.

示例：

using System;
 
namespace DoFactory.GangOfFour.Proxy.Structural
{
  /// <summary>
  /// MainApp startup class for Structural
  /// Proxy Design Pattern.
  /// </summary>
  class MainApp
  {
    /// <summary>
    /// Entry point into console application.
    /// </summary>
    static void Main()
    {
      // Create proxy and request a service
      Proxy proxy = new Proxy();
      proxy.Request();
 
      // Wait for user
      Console.ReadKey();
    }
  }
 
  /// <summary>
  /// The 'Subject' abstract class
  /// </summary>
  abstract class Subject
  {
    public abstract void Request();
  }
 
  /// <summary>
  /// The 'RealSubject' class
  /// </summary>
  class RealSubject : Subject
  {
    public override void Request()
    {
      Console.WriteLine("Called RealSubject.Request()");
    }
  }
 
  /// <summary>
  /// The 'Proxy' class
  /// </summary>
  class Proxy : Subject
  {
    private RealSubject _realSubject;
 
    public override void Request()
    {
      // Use 'lazy initialization'
      if (_realSubject == null)
      {
        _realSubject = new RealSubject();
      }
 
      _realSubject.Request();
    }
  }
}

Output

Called RealSubject.Request()

实际运用：

using System;
 
namespace DoFactory.GangOfFour.Proxy.RealWorld
{
  /// <summary>
  /// MainApp startup class for Real-World
  /// Proxy Design Pattern.
  /// </summary>
  class MainApp
  {
    /// <summary>
    /// Entry point into console application.
    /// </summary>
    static void Main()
    {
      // Create math proxy
      MathProxy proxy = new MathProxy();
 
      // Do the math
      Console.WriteLine("4 + 2 = " + proxy.Add(4, 2));
      Console.WriteLine("4 - 2 = " + proxy.Sub(4, 2));
      Console.WriteLine("4 * 2 = " + proxy.Mul(4, 2));
      Console.WriteLine("4 / 2 = " + proxy.Div(4, 2));
 
      // Wait for user
      Console.ReadKey();
    }
  }
 
  /// <summary>
  /// The 'Subject interface
  /// </summary>
  public interface IMath
  {
    double Add(double x, double y);
    double Sub(double x, double y);
    double Mul(double x, double y);
    double Div(double x, double y);
  }
 
  /// <summary>
  /// The 'RealSubject' class
  /// </summary>
  class Math : IMath
  {
    public double Add(double x, double y) { return x + y; }
    public double Sub(double x, double y) { return x - y; }
    public double Mul(double x, double y) { return x * y; }
    public double Div(double x, double y) { return x / y; }
  }
 
  /// <summary>
  /// The 'Proxy Object' class
  /// </summary>
  class MathProxy : IMath
  {
    private Math _math = new Math();
 
    public double Add(double x, double y)
    {
      return _math.Add(x, y);
    }
    public double Sub(double x, double y)
    {
      return _math.Sub(x, y);
    }
    public double Mul(double x, double y)
    {
      return _math.Mul(x, y);
    }
    public double Div(double x, double y)
    {
      return _math.Div(x, y);
    }
  }
}

Output

4 + 2 = 6
4 - 2 = 2
4 * 2 = 8
4 / 2 = 2