Abstract Class VS Interface[二]

StrategyPattern，这个实例想做一个策略者：把已经声明过的方法操作，在运行时进行调换。猛地一听好像有些奇怪，类中的某个方法已经声明过了，怎么能在运行时,替换它的实际的处理过程呢,只留了个方法名而作别的事情。StrategyPattern就是实现了这样的操作。

IStrategyDraw IStrategyDraw Interface
using System;
namespace StrategyPattern
{
  /// <summary>
  /// Summary description for IStrategyDraw.
  /// </summary>
  public interface IStrategyDraw
  {
    //here just define a general draw function.
    string StragegyDraw();
  }
}

GeneralDraw GeneralDraw Class
using System;
namespace StrategyPattern
{
  /// <summary>
  /// Summary description for GeneralDraw.
  /// </summary>
  public class GeneralDraw
  {
    private IStrategyDraw _strategyDraw;

    public GeneralDraw()
    {
    }

    public IStrategyDraw StrategyDraw
    {
      get
      {
        return this._strategyDraw;
      }
      set
      {
        this._strategyDraw = value;
      }
    }

    public string StragegyDraw()
    {
      if (this._strategyDraw != null)
      {
        return this._strategyDraw.StragegyDraw();
      }
      else
      {
        return "";
      }
    }

    public string SelfDraw()
    {
      return "Self Draw";
    }

  }
}

ConsoleStrategy ConsoleStrategy Class
using System;
namespace StrategyPattern
{
  /// <summary>
  /// Summary description for ConsoleStrategy.
  /// </summary>
  public class ConsoleStrategy : IStrategyDraw
  {
    public ConsoleStrategy()
    {
    }

    #region IStrategyDraw Members

    public string StragegyDraw()
    {
      return "Console Draw";
    }

    #endregion
  }
}

WindowStategy WindowStategy Class
using System;
namespace StrategyPattern
{
  /// <summary>
  /// Summary description for WindowStategy.
  /// </summary>
  public class WindowStategy:IStrategyDraw
  {
    public WindowStategy()
    {
    }

    #region IStrategyDraw Members

    public string StragegyDraw()
    {
      return "Window Draw";
    }

    #endregion
  }
}

StrategyDraw Test Code
private void StrategyDraw()
{
  IStrategyDraw conStrategy = new ConsoleStrategy();
  IStrategyDraw winStrategy = new WindowStategy();
  GeneralDraw genDraw = new GeneralDraw();
  genDraw.StrategyDraw = conStrategy;

  Console.WriteLine("{0}",genDraw.StragegyDraw());
  Console.WriteLine("{0}",genDraw.SelfDraw());

  genDraw.StrategyDraw = winStrategy;
  Console.WriteLine("{0}",genDraw.StragegyDraw());
  Console.WriteLine("{0}",genDraw.SelfDraw());
}
　　　GeneralDraw在运行时，根据自己内部的的IStrategyDraw确定Draw方法的实际操作，而外表上看GeneralDraw只给外界公开说自己有一个Draw方法。
　　　在上面的两个设计模式中，DecoratorPattern中的ComponentDecorator这个AbstractClass体现了Class一级的抽象，AbstractClass提供给了子类共有的属性和方法。在DecoratorPattern和StrategyPattern中多出用到Interface，体现了Interface是方法一级的抽象。

所有代码在Windows 2003 Enterprise + VS 2003 Enterprise 下编译通过

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