C#设计模式之二十一访问者模式（Visitor Pattern）【行为型】

  1 namespace Vistor
  2 {
  3     //抽象图形定义---相当于“抽象节点角色”Element
  4     public abstract class Shape
  5     {
  6         画图形
  7         void Draw();
  8         外界注入具体访问者
  9          Accept(ShapeVisitor visitor);
 10     }
 11 
 12     抽象访问者 Visitor
 13      ShapeVisitor
 14  15          Visit(Rectangle shape);
 16 
 17          Visit(Circle shape);
 18 
 19          Visit(Line shape);
 20 
 21         这里有一点要说：Visit方法的参数可以写成Shape吗？就是这样 Visit(Shape shape)，当然可以，但是ShapeVisitor子类Visit方法就需要判断当前的Shape是什么类型，是Rectangle类型，是Circle类型，或者是Line类型。
 22  23 
 24     具体访问者 ConcreteVisitor
 25     sealed  CustomVisitor : ShapeVisitor
 26  27         针对Rectangle对象
 28         override  Visit(Rectangle shape)
 29         {
 30             Console.WriteLine("针对Rectangle新的操作！");
 31         }
 32         针对Circle对象
 33          Visit(Circle shape)
 34  35             Console.WriteLine(针对Circle新的操作！ 36  37         针对Line对象
 38          Visit(Line shape)
 39  40             Console.WriteLine(针对Line新的操作！ 41  42  43 
 44     矩形----相当于“具体节点角色” ConcreteElement
 45      Rectangle : Shape
 46  47          Draw()
 48  49             Console.WriteLine(矩形我已经画好！ 50  51 
 52          Accept(ShapeVisitor visitor)
 53  54             visitor.Visit(this 55  56  57 
 58     圆形---相当于“具体节点角色”ConcreteElement
 59      Circle : Shape
 60  61          62  63             Console.WriteLine(圆形我已经画好！ 64  65 
 66          67  68             visitor.Visit( 69  70  71 
 72     直线---相当于“具体节点角色” ConcreteElement
 73      Line : Shape
 74  75          76  77             Console.WriteLine(直线我已经画好！ 78  79 
 80          81  82             visitor.Visit( 83  84  85 
 86     结构对象角色
 87     internal  AppStructure
 88  89         private ShapeVisitor _visitor;
 90 
 91         public AppStructure(ShapeVisitor visitor)
 92  93             this._visitor = visitor;
 94  95 
 96          Process(Shape shape)
 97  98             shape.Accept(_visitor);
 99 100 101 
102      Program
103 104         static void Main(string[] args)
105 106             如果想执行新增加的操作
107             ShapeVisitor visitor = new CustomVisitor();
108             AppStructure app =  AppStructure(visitor);
109 
110             Shape shape =  Rectangle();
111             shape.Draw();执行自己的操作
112             app.Process(shape);执行新的操作
113 
114 
115             shape =  Circle();
116             shape.Draw();117             app.Process(shape);118 
119 
120             shape =  Line();
121             shape.Draw();122             app.Process(shape);123 
124 
125             Console.ReadLine();
126 127 128 }

 Visitor
抽象访问者角色 Visitor
 PutTelevision(Television tv);
  7 
 PutComputer(Computer comp);
  9  10 
 11     具体访问者角色 ConcreteVisitor
 SizeVisitor : Visitor
 13  14          PutTelevision(Television tv)
 15  16             Console.WriteLine(按商品大小{0}排放,tv.Size);
 17  PutComputer(Computer comp)
 20  21             Console.WriteLine( 23  24 
 26      StateVisitor : Visitor
 27 按商品新旧值{0}排放 32 
 37  38 
 39     抽象节点角色 Element
 40      Goods
 42          Operate(Visitor visitor);
 44         private int nSize;
 45          Size
 47             get { return nSize; }
 48             set { nSize = value; }
 49  50 
 51          nState;
 State
 54              nState; }
 55             set { nState = 57  58 
具体节点角色 ConcreteElement
 60      Television : Goods
 61  62          Operate(Visitor visitor)
 63  64             visitor.PutTelevision( 65  66  67 
 68      69      Computer : Goods
 71          72  73             visitor.PutComputer( 75  76 
 77      78      StoragePlatform
 79 private IList<Goods> list = new List<Goods>();
 81 
 82          Attach(Goods element)
            list.Add(element);
 85  86 
 87          Detach(Goods element)
 89             list.Remove(element);
 90  91 
 92          93  94             foreach (Goods g in list)
 95             {
 96                 g.Operate(visitor);
            }
100 
101     102 103         104 105             StoragePlatform platform =  StoragePlatform();
106             platform.Attach( Television());
107             platform.Attach( Computer());
108 
109             SizeVisitor sizeVisitor =  SizeVisitor();
110             StateVisitor stateVisitor =  StateVisitor();
111 
112             platform.Operate(sizeVisitor);
113             platform.Operate(stateVisitor);
115             Console.Read();
116 117 118 }