迭代器模式和组合模式（head first设计模式——8）
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(); } }
