2022行為型模式C#疊代器模式（Iterator Pattern），不進來？

疊代器設計模式提供了一種按順序通路聚合對象的元素的方法，而不公開其基礎表示形式。

UML類圖

C# 中的結構代碼

#

此結構代碼示範了疊代器模式，該模式提供了一種周遊（疊代）項集合的方法，而無需詳細說明集合的基礎結構。

• using System;
• using System.Collections.Generic;
• namespace Iterator.Structural
• {
• /// <summary>
• /// Iterator Design Pattern
• /// </summary>
• public class Program
• public static void Main(string[] args)
• ConcreteAggregate a = new ConcreteAggregate();
• a[0] = "Item A";
• a[1] = "Item B";
• a[2] = "Item C";
• a[3] = "Item D";
• // Create Iterator and provide aggregate
• Iterator i = a.CreateIterator();
• Console.WriteLine("Iterating over collection:");
• object item = i.First();
• while (item != null)
• Console.WriteLine(item);
• item = i.Next();
• }
• // Wait for user
• Console.ReadKey();
• /// The 'Aggregate' abstract class
• public abstract class Aggregate
• public abstract Iterator CreateIterator();
• /// The 'ConcreteAggregate' class
• public class ConcreteAggregate : Aggregate
• List<object> items = new List<object>();
• public override Iterator CreateIterator()
• return new ConcreteIterator(this);
• // Get item count
• public int Count
• get { return items.Count; }
• // Indexer
• public object this[int index]
• get { return items[index]; }
• set { items.Insert(index, value); }
• /// The 'Iterator' abstract class
• public abstract class Iterator
• public abstract object First();
• public abstract object Next();
• public abstract bool IsDone();
• public abstract object CurrentItem();
• /// The 'ConcreteIterator' class
• public class ConcreteIterator : Iterator
• ConcreteAggregate aggregate;
• int current = 0;
• // Constructor
• public ConcreteIterator(ConcreteAggregate aggregate)
• this.aggregate = aggregate;
• // Gets first iteration item
• public override object First()
• return aggregate[0];
• // Gets next iteration item
• public override object Next()
• object ret = null;
• if (current < aggregate.Count - 1)
• ret = aggregate[++current];
• return ret;
• // Gets current iteration item
• public override object CurrentItem()
• return aggregate[current];
• // Gets whether iterations are complete
• public override bool IsDone()
• return current >= aggregate.Count;

C# 中的實際代碼

此實際代碼示範了疊代器模式，該模式用于循環通路項集合，并在每次疊代中跳過特定數量的項。

• namespace Iterator.RealWorld
• // Build a collection
• Collection collection = new Collection();
• collection[0] = new Item("Item 0");
• collection[1] = new Item("Item 1");
• collection[2] = new Item("Item 2");
• collection[3] = new Item("Item 3");
• collection[4] = new Item("Item 4");
• collection[5] = new Item("Item 5");
• collection[6] = new Item("Item 6");
• collection[7] = new Item("Item 7");
• collection[8] = new Item("Item 8");
• // Create iterator
• Iterator iterator = collection.CreateIterator();
• // Skip every other item
• iterator.Step = 2;
• for (Item item = iterator.First();
• !iterator.IsDone; item = iterator.Next())
• Console.WriteLine(item.Name);
• /// A collection item
• public class Item
• string name;
• public Item(string name)
• this.name = name;
• public string Name
• get { return name; }
• /// The 'Aggregate' interface
• public interface IAbstractCollection
• Iterator CreateIterator();
• public class Collection : IAbstractCollection
• List<Item> items = new List<Item>();
• public Iterator CreateIterator()
• return new Iterator(this);
• // Gets item count
• public Item this[int index]
• set { items.Add(value); }
• /// The 'Iterator' interface
• public interface IAbstractIterator
• Item First();
• Item Next();
• bool IsDone { get; }
• Item CurrentItem { get; }
• public class Iterator : IAbstractIterator
• Collection collection;
• int step = 1;
• public Iterator(Collection collection)
• this.collection = collection;
• // Gets first item
• public Item First()
• current = 0;
• return collection[current] as Item;
• // Gets next item
• public Item Next()
• current += step;
• if (!IsDone)
• else
• return null;
• // Gets or sets stepsize
• public int Step
• get { return step; }
• set { step = value; }
• // Gets current iterator item
• public Item CurrentItem
• get { return collection[current] as Item; }
• // Gets whether iteration is complete
• public bool IsDone
• get { return current >= collection.Count; }