c#设计模式-结构型模式-4.组合模式

Posted 2021-05-29 mr.chenyuelin

组合模式：将对象组合成树形结构以表示“整体-部分”的关系

比较形象的比喻，俄罗斯套娃

例子，比如一个文件下有ppt，word，子文件夹，子文件下又可以装东西
一个公司下可以有很多部门，部门下有员工

如果当前节点为word就不能创建文件夹了，只能编辑，所以组合模式分为透明式和安全式

透明式：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace 透明式组合模式
{
    public abstract class Folder
    {
        public abstract void Add(Folder folder);

        public abstract void Remove(Folder folder);

        public abstract void Open();
    }

    public sealed class Word : Folder
    {
    	//因为word下无法创建文件，所以抛出异常
        public override void Add(Folder folder)
        {
            throw new NotImplementedException();
        }

        public override void Open()
        {
            Console.WriteLine("打开word开始编辑");
        }

        public override void Remove(Folder folder)
        {
            throw new NotImplementedException();
        }
    }

    public class SonFolder : Folder
    {
        public override void Add(Folder folder)
        {
            Console.WriteLine("在当前目录下添加文件");
        }

        public override void Open()
        {
            Console.WriteLine("打开文件");
        }

        public override void Remove(Folder folder)
        {
            Console.WriteLine("在当前目录下删除文件");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Folder myword = new Word();
            myword.Open();
            //word下不可创建文件会抛出异常，所以这是透明式的短板
            //myword.Add(new SonFolder());
            //myword.Remove(new SonFolder());

            Folder myfolder = new SonFolder();
            myfolder.Open();

            myfolder.Add(new SonFolder());
            myfolder.Remove(new SonFolder());
        }
    }
}

透明式把抽象构件父类的抽象方法都申明出来，导致子类没有该功能也要重写，显得不安全

而安全式，抽象构件父类只写了子类共有的方法，比如open方法

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace 安全式组合模式
{
    public abstract class Folder
    {    

        public abstract void Open();
    }

    public sealed class Word : Folder
    {      
        public override void Open()
        {
            Console.WriteLine("打开word开始编辑");
        }
    }

    public abstract class SonFolder : Folder
    {
        public abstract void Add(Folder folder);

        public abstract void Remove(Folder folder);   

        public override void Open()
        {
            Console.WriteLine("打开当前文件");
        }
    }

    public class NextFolder : SonFolder
    {
        public override void Add(Folder folder)
        {
            Console.WriteLine("添加文件");
        }

        public override void Remove(Folder folder)
        {
            Console.WriteLine("删除文件");
        }

        public override void Open()
        {
            Console.WriteLine("打开当前文件");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Folder myword = new Word();
            myword.Open();           

            Folder nextfolder = new NextFolder();
            nextfolder.Open();

            (nextfolder as SonFolder).Add(new NextFolder());
            (nextfolder as SonFolder).Remove(new NextFolder());
        }
    }
}