C# 迭代器模式讲解和代码示例

using System; using System.Collections; using System.Collections.Generic; namespace RefactoringGuru.DesignPatterns.Iterator.Conceptual { abstract class Iterator : IEnumerator { object IEnumerator.Current => Current(); // Returns the key of the current element public abstract int Key(); // Returns the current element public abstract object Current(); // Move forward to next element public abstract bool MoveNext(); // Rewinds the Iterator to the first element public abstract void Reset(); } abstract class IteratorAggregate : IEnumerable { // Returns an Iterator or another IteratorAggregate for the implementing // object. public abstract IEnumerator GetEnumerator(); } // Concrete Iterators implement various traversal algorithms. These classes // store the current traversal position at all times. class AlphabeticalOrderIterator : Iterator { private WordsCollection _collection; // Stores the current traversal position. An iterator may have a lot of // other fields for storing iteration state, especially when it is // supposed to work with a particular kind of collection. private int _position = -1; private bool _reverse = false; public AlphabeticalOrderIterator(WordsCollection collection, bool reverse = false) { this._collection = collection; this._reverse = reverse; if (reverse) { this._position = collection.getItems().Count; } } public override object Current() { return this._collection.getItems()[_position]; } public override int Key() { return this._position; } public override bool MoveNext() { int updatedPosition = this._position + (this._reverse ? -1 : 1); if (updatedPosition >= 0 && updatedPosition < this._collection.getItems().Count) { this._position = updatedPosition; return true; } else { return false; } } public override void Reset() { this._position = this._reverse ? this._collection.getItems().Count - 1 : 0; } } // Concrete Collections provide one or several methods for retrieving fresh // iterator instances, compatible with the collection class. class WordsCollection : IteratorAggregate { List<string> _collection = new List<string>(); bool _direction = false; public void ReverseDirection() { _direction = !_direction; } public List<string> getItems() { return _collection; } public void AddItem(string item) { this._collection.Add(item); } public override IEnumerator GetEnumerator() { return new AlphabeticalOrderIterator(this, _direction); } } class Program { static void Main(string[] args) { // The client code may or may not know about the Concrete Iterator // or Collection classes, depending on the level of indirection you // want to keep in your program. var collection = new WordsCollection(); collection.AddItem("First"); collection.AddItem("Second"); collection.AddItem("Third"); Console.WriteLine("Straight traversal:"); foreach (var element in collection) { Console.WriteLine(element); } Console.WriteLine("\nReverse traversal:"); collection.ReverseDirection(); foreach (var element in collection) { Console.WriteLine(element); } } } } 

Straight traversal: First Second Third Reverse traversal: Third Second First