[转载] C#面向对象设计模式纵横谈——24 Visitor访问者模式

主讲：李建忠

来源：http://www.microsoft.com/china/msdn/events/webcasts/shared/webcast/consyscourse/CsharpOOD.aspx

 

 

   1:  public abstract class Shape

   2:  {

   3:      public abstract void Draw();

   4:   

   5:      //预料到将来可能会引入新的操作

   6:      public abstract void Accept(ShapeVisitor v);

   7:  }

   8:   

   9:  public abstract class ShapeVisitor

  10:  {

  11:      public abstract void Visit(Rectangle shape);    //#1

  12:      public abstract void Visit(Circle shape);    //#2

  13:      public abstract void Visit(Line shape);    //#3

  14:  }

  15:   

  16:  public class MyVisitor:ShapeVisitor

  17:  {

  18:      public override void Visit(Rectangle shape);    //#1

  19:      {

  20:          //增加对Rectangle的操作

  21:      }

  22:   

  23:      public override void Visit(Circle shape);    //#2

  24:      {

  25:          //增加对Circle的操作

  26:      }

  27:   

  28:      public override void Visit(Line shape);    //#3

  29:      {

  30:          //增加对Line的操作

  31:      }

  32:  }

  33:   

  34:  public class Rectangle:Shape

  35:  {

  36:      public override void Draw()

  37:      {

  38:          //...

  39:      }

  40:   

  41:      public override void Accept(ShapeVisitor v)

  42:      {

  43:          v.Visit(this);    //调用 #1

  44:      }

  45:  }

  46:   

  47:  public class Circle:Shape

  48:  {

  49:      public override void Draw()

  50:      {

  51:          //...

  52:      }

  53:   

  54:      public override void Accept(ShapeVisitor v)

  55:      {

  56:          v.Visit(this);    //调用 #2

  57:      }

  58:  }

  59:   

  60:  public class Line:Shape

  61:  {

  62:      public override void Draw()

  63:      {

  64:          //...

  65:      }

  66:   

  67:      public override void Accept(ShapeVisitor v)

  68:      {

  69:          v.Visit(this);     //调用 #3

  70:      }

  71:  }

  72:   

  73:  class App

  74:  {

  75:      ShapeVisitor visitor;

  76:      public App(ShapeVisitor visitor)

  77:      {

  78:          this.visitor=visitor;

  79:      }

  80:   

  81:      public static void Process(Shape shape)

  82:      {

  83:          //两处多态：

  84:          //1.Accept方法的调用对象 shape

  85:          //2.Accept等方法的参数 visitor

  86:          shape.Accept(visitor);

  87:      }

  88:  }

  89:   

  90:  App app=new App(new MyVisitor());

  91:  app.Process(new Line());

 

转载于:https://www.cnblogs.com/6DAN_HUST/archive/2012/10/18/2728995.html