将数据结构与数据操作分离, 用于稳定的数据结构和易变的操作耦合问题
访问者模式
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| abstract class Visitor
{
public abstract void VisitorConcreateElementA(ConcreateElementA concreateElementA);
public abstract void VisitorConcreateElementB(ConcreateElementB concreateElementB);
}
class ConcreateVisitor1 : Visitor
{
public override void VisitorConcreateElementA(ConcreateElementA concreateElementA)
{
Console.WriteLine("{0}被{1}访问", ConcreateElementA.GetType().Name, this.GetType().Name);
}
public override void VisitorConcreateElementB(ConcreateElementB concreateElementB)
{
Console.WriteLine("{0}被{1}访问", ConcreateElementB.GetType().Name, this.GetType().Name);
}
}
class ConcreateVisitor2 : Visitor
{
}
abstract class Element
{
public abstract void Accept(Visitor visitor);
}
class ConcreateElementA : Element
{
public override void Accept(Visitor visitor)
{
visitor.VisitConcreateElementA(this);
}
public void OperationA()
{}
}
class ConcreateElementB : Element
{
public override void Accept(Visitor visitor)
{
visitor.VisitConcreateElementB(this);
}
public void OperationB()
{}
}
class ObjectStructure
{
private IList<Element> elements = new List<Element>();
public void Attach(Element element)
{
elements.Add(element);
}
public void Detach(Element element)
{
elements.Remove(element);
}
public void Accept(Visitor visitor)
{
elements.Foreach(e => e.Accept(visitor));
}
}
ObjectStructure o = new ObjectStructure();
o.Attach(new ConcreateElementA);
o.Attach(new ConcreateElementB);
ConcreateVisitor1 v1 = new ConcreateVisitor1();
ConcreateVisitor1 v2 = new ConcreateVisitor2();
o.Accept(v1);
o.Accept(v2);
|