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把迭代器模式和组合模式放在同一篇的原因是其联系比较紧密。

一、迭代器模式

1.1迭代器模式定义

迭代器模式提供一种方法顺序访问一个聚合对象中的各个元素，而不是暴露其内部的表示。

这个模式提供了一种方法，可以顺序访问一个聚合对象中的元素，而不用知道内部怎么表示的。为了更好的理解迭代器模式，我们举个例子。

1.2迭代器例子

下面使用head first设计模式中的例子，使用迭代器模式来演示早餐和晚餐菜单的显示。由于早餐和晚餐其数据结构不同，由于早餐店和晚餐店需要合并，所以需要一个统一的菜单：即菜单项结构相同。下面先介绍一下菜单项的结构。

public class MenuItem{private string name;private string description;private bool vegetarin;private double price;public MenuItem(string name, string description, bool vegetarin, double price){this.name = name;this.description = description;this.vegetarin = vegetarin;this.price = price;}public string GetName(){return name;}public double GetPrice(){return price;}public bool IsVegetarian(){return vegetarin;}public string GetDescription(){return description;}       }

接下来分别来看一下早餐类和晚餐类,早餐类的结构是ArrayList，晚餐类的结构是数组：

public class BreakfastMenu{ArrayList menuItems;public BreakfastMenu(){menuItems = new ArrayList();AddItem("牛奶", "牛奶description", false, 3.0);AddItem("油条","油条description",false,1.0);AddItem("馒头","馒头description",true,1.0);AddItem("豆浆", "DoujiangDescription", true, 1.5);}public void AddItem(string name, string description, bool vegetarian, double price){MenuItem menuItem = new MenuItem( name,  description,  vegetarian,  price);menuItems.Add(menuItem);}public ArrayList GetMenuItems(){return menuItems;}}public class DinerMenu{static readonly int Max_ITEMS = 6;int numberOfItems = 0;MenuItem[] menuItems;public DinerMenu(){menuItems = new MenuItem[Max_ITEMS];AddItem("香菇豆腐饭", "香菇豆腐", false, 10.5);AddItem("蛋炒饭","哈哈",false,8.5);AddItem("鱼香肉丝","你猜",true,15.5);}public void AddItem(string name, string description, bool vegetarian, double price){MenuItem menuItem = new MenuItem(name, description, vegetarian, price);if (numberOfItems>Max_ITEMS){Console.WriteLine("菜单已满");}else{menuItems[numberOfItems] = menuItem;numberOfItems++;}}public MenuItem[] GetMenuItems(){return menuItems;}}

接下来看一下客户端是如何来把各种饭菜打印出来的：

BreakfastMenu breakfastMenu = new BreakfastMenu();ArrayList breakfastItems = breakfastMenu.GetMenuItems();DinerMenu dinerMenu = new DinerMenu();MenuItem[] lunchItems = dinerMenu.GetMenuItems();for (int i = 0; i < breakfastItems.Count; i++){MenuItem menuItem = breakfastItems[i] as MenuItem;Console.WriteLine(menuItem.GetName()+" "+menuItem.GetPrice().ToString()+" "+menuItem.GetDescription().ToString());}for (int j = 0; j < lunchItems.Length; j++){MenuItem lunchItem = lunchItems[j] ;if (lunchItem!=null){Console.WriteLine(lunchItem.GetName() + " " + lunchItem.GetPrice().ToString() + " " + lunchItem.GetDescription().ToString());}}Console.ReadKey();

很明显上面的遍历的算法是一样的，因为早餐和晚餐的数据结构的不同导致了代码不能复用，当然可以使用泛型解决该问题。但是本文需要使用的是迭代器设计模式。

为了可以使用相同的遍历方法，我们定义一个接口迭代器：

public interface Iterator{/// <summary>/// 用来判断下一个元素是否为空/// </summary>/// <returns></returns>bool HasNext();/// <summary>/// 用来获取当前元素/// </summary>/// <returns></returns>object Next();}

我们希望的是能通过迭代器实现下面的操作：

while (iterator.HasNext()){MenuItem menuitem = (MenuItem)iterator.Next;Console.WriteLine(menuitem.GetName() + " " + menuitem.GetPrice().ToString() + " " + menuitem.GetDescription().ToString());}

接下来的目标就是创建早晚餐菜单的迭代器。

public class BreakfastIterator : Iterator{private ArrayList items;private int position;public BreakfastIterator(ArrayList arrayList){items = arrayList;}public bool HasNext(){if (position>items.Count||items[position]==null){return false;}else{return true;}}public object Next(){MenuItem menuItem = items[position] as MenuItem;position = position + 1;return menuItem;}}public class DinnerIterator : Iterator{private MenuItem[] items;private int position = 0;public DinnerIterator(MenuItem[] items){this.items = items;}public bool HasNext(){if (position > items.Length || items[position] == null){return false;}else{return true;}}public object Next(){MenuItem menuItem = items[position] as MenuItem;position = position + 1;return menuItem;}}

可以定义一个菜单接口，来创建迭代器。分别让各个菜单去实现这个接口，下面给出完整的代码：

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;namespace IteratorPattern
{class Program{static void Main(string[] args){//BreakfastMenu breakfastMenu = new BreakfastMenu();//ArrayList breakfastItems = breakfastMenu.GetMenuItems();//DinerMenu dinerMenu = new DinerMenu();//MenuItem[] lunchItems = dinerMenu.GetMenuItems();//for (int i = 0; i < breakfastItems.Count; i++)//{//    MenuItem menuItem = breakfastItems[i] as MenuItem;//    Console.WriteLine(menuItem.GetName() + " " + menuItem.GetPrice().ToString() + " " + menuItem.GetDescription().ToString());//}//for (int j = 0; j < lunchItems.Length; j++)//{//    MenuItem lunchItem = lunchItems[j];//    if (lunchItem != null)//    {//        Console.WriteLine(lunchItem.GetName() + " " + lunchItem.GetPrice().ToString() + " " + lunchItem.GetDescription().ToString());//    }//}IMenu breakfastMenu = new BreakfastMenu();IMenu dinnerMenu = new DinnerMenu();breakfastMenu.CreateIterator();Iterator dinnerIterator = dinnerMenu.CreateIterator();Iterator breakfastIterator = breakfastMenu.CreateIterator();Print(breakfastIterator);Print(dinnerIterator);Console.ReadKey();}static void Print(Iterator iterator){while (iterator.HasNext()){MenuItem menuItem = (MenuItem)iterator.Next();Console.WriteLine(menuItem.GetName() + " " + menuItem.GetPrice().ToString() + " " + menuItem.GetDescription().ToString());}}}public class MenuItem{private string name;private string description;private bool vegetarin;private double price;public MenuItem(string name, string description, bool vegetarin, double price){this.name = name;this.description = description;this.vegetarin = vegetarin;this.price = price;}public string GetName(){return name;}public double GetPrice(){return price;}public bool IsVegetarian(){return vegetarin;}public string GetDescription(){return description;}}public class BreakfastMenu : IMenu{ArrayList menuItems;public BreakfastMenu(){menuItems = new ArrayList();AddItem("牛奶", "牛奶description", false, 3.0);AddItem("油条","油条description",false,1.0);AddItem("馒头","馒头description",true,1.0);AddItem("豆浆", "DoujiangDescription", true, 1.5);}public void AddItem(string name, string description, bool vegetarian, double price){MenuItem menuItem = new MenuItem( name,  description,  vegetarian,  price);menuItems.Add(menuItem);}public ArrayList GetMenuItems(){return menuItems;}public Iterator CreateIterator(){return new BreakfastIterator(menuItems);}}public class DinnerMenu:IMenu{static readonly int Max_ITEMS = 6;int numberOfItems = 0;MenuItem[] menuItems;public DinnerMenu(){menuItems = new MenuItem[Max_ITEMS];AddItem("香菇豆腐饭", "香菇豆腐", false, 10.5);AddItem("蛋炒饭","哈哈",false,8.5);AddItem("鱼香肉丝","你猜",true,15.5);}public void AddItem(string name, string description, bool vegetarian, double price){MenuItem menuItem = new MenuItem(name, description, vegetarian, price);if (numberOfItems>Max_ITEMS){Console.WriteLine("菜单已满");}else{menuItems[numberOfItems] = menuItem;numberOfItems++;}}public MenuItem[] GetMenuItems(){return menuItems;}public Iterator CreateIterator(){return new DinnerIterator(menuItems);}}public interface Iterator{/// <summary>/// 用来判断下一个元素是否为空/// </summary>/// <returns></returns>bool HasNext();/// <summary>/// 用来获取当前元素/// </summary>/// <returns></returns>object Next();}public class BreakfastIterator : Iterator{private ArrayList items;private int position;public BreakfastIterator(ArrayList arrayList){items = arrayList;}public bool HasNext(){if (position>=items.Count||items[position]==null){return false;}else{return true;}}public object Next(){MenuItem menuItem = items[position] as MenuItem;position = position + 1;return menuItem;}}public class DinnerIterator : Iterator{private MenuItem[] items;private int position = 0;public DinnerIterator(MenuItem[] items){this.items = items;}public bool HasNext(){if (position > items.Length || items[position] == null){return false;}else{return true;}}public object Next(){MenuItem menuItem = items[position] as MenuItem;position = position + 1;return menuItem;}}public interface IMenu{Iterator CreateIterator();}}

迭代器模式主要是聚合对象创建迭代器，借助单一职责的原则，从而实现客户端可以对聚合的各种对象实现相同的操作，达到代码复用的效果。

1.3迭代器模式类图

下面看看上面代码的类图，

然后再看看迭代器模式的类图。

二、组合模式

2.1组合模式定义

组合模式允许将对象组合成属性结构来表现“整体/部分”层次结构，组合能让客户以一致的方式处理个别对象以及对象组合。

2.2组合模式例子

下面是组合模式的例子：

class Program { static void Main(string[] args) { //定义早餐==================================================================== MenuComponent menu = new Menu("早餐", "新鲜的早餐");MenuComponent menuItem1 = new MenuItem("牛奶", "牛奶description", false, 3.0); MenuComponent menuItem2 = new MenuItem("油条", "油条description", false, 1.0); MenuComponent menuItem3 = new MenuItem("馒头", "馒头description", true, 1.0); MenuComponent menuItem4 = new MenuItem("豆浆", "DoujiangDescription", true, 1.5); menu.Add(menuItem1); menu.Add(menuItem2); menu.Add(menuItem3); menu.Add(menuItem4);//定义午餐==================================================================== MenuComponent lunch = new Menu("午餐", "包括下午茶"); MenuComponent lunch1=new  MenuItem("香菇豆腐饭", "香菇豆腐", false, 10.5); MenuComponent lunch2 = new MenuItem("蛋炒饭", "哈哈", false, 8.5); MenuComponent lunch3 = new MenuItem("鱼香肉丝", "你猜", true, 15.5); MenuComponent tea = new Menu("下午茶", "新鲜的下午茶");MenuComponent tea1 = new MenuItem("香蕉片", "香蕉片", true, 10); MenuComponent tea2 = new MenuItem("咖啡", "大杯的哦", true, 10); tea.Add(tea1); tea.Add(tea2);lunch.Add(lunch1); lunch.Add(lunch2); lunch.Add(lunch3); lunch.Add(tea);//定义三餐==================================================================== MenuComponent food = new Menu("三餐", "三餐列表"); food.Add(menu); food.Add(lunch); food.Print(); Console.ReadKey(); }}/// <summary> /// 菜单组件 /// </summary> public abstract class MenuComponent { public abstract void Add(MenuComponent menucomponent);public abstract  void Remove(MenuComponent menucomponent);public abstract MenuComponent GetChild(int i);public abstract string GetDescription();public abstract string GetName();public abstract double GetPrice();public abstract bool IsVegetarian(); public abstract void Print(); }public class MenuItem:MenuComponent { private string name; private string description; private bool vegetarin; private double price;public MenuItem(string name, string description, bool vegetarin, double price) { this.name = name; this.description = description; this.vegetarin = vegetarin; this.price = price; }public override  string GetName() { return name; }public override double GetPrice() { return price; }public override bool IsVegetarian() { return vegetarin; }public override string GetDescription() { return description; }public override void Print() { Console.Write(""+GetName()+","); if (IsVegetarian()) { Console.Write("（素） ,"); } Console.Write(GetPrice()+"￥,"); Console.WriteLine(GetDescription()+"。"); }public override MenuComponent GetChild(int i) { throw new NotImplementedException(); }public override void Add(MenuComponent menucomponent) { throw new NotImplementedException(); }public override void Remove(MenuComponent menucomponent) { throw new NotImplementedException(); } }public class Menu : MenuComponent { ArrayList menuComponents = new ArrayList(); private string name; private string description;public Menu(string name, string description) { this.name = name; this.description = description; }public override void Add(MenuComponent menucomponent) { menuComponents.Add(menucomponent); return; }public override void Remove(MenuComponent menucomponent) { menuComponents.Remove(menucomponent); }public override string GetName() { return name; }public override string GetDescription() { return description; }public override void Print() { Console.Write("--"+GetName()); Console.WriteLine("," + GetDescription());IEnumerator enumerator = menuComponents.GetEnumerator(); while (enumerator.MoveNext()) { MenuComponent menuComponent = (MenuComponent)enumerator.Current; menuComponent.Print(); } } public override MenuComponent GetChild(int i) { throw new NotImplementedException(); } public override double GetPrice() { throw new NotImplementedException(); }public override bool IsVegetarian() { throw new NotImplementedException(); } }