using System;using System.Collections;using System.Collections.Generic;namespace LineNodeDemo{ class Program {  static void Main(string[] args)  {   LineNodeCollection lineNodes = new LineNodeCollection();   lineNodes.Add(new LineNode("N1") { Name = "Microsoft" });   lineNodes.Add(new LineNode("N2") { Name = "Lenovo" });   lineNodes.Add(new LineNode("N3") { Name = "Apple" });   lineNodes.Add(new LineNode("N4") { Name = "China Mobile" });   Console.WriteLine("1、顯示全部：");   lineNodes.ForEach(x => { Console.WriteLine(x.Name); });   Console.WriteLine("2、刪除編號為N2的元素：");   lineNodes.Remove("N2");   lineNodes.ForEach(x => { Console.WriteLine(x.Name); });   Console.WriteLine("3、刪除索引為1的元素：");   lineNodes.RemoveAt(1);   lineNodes.ForEach(x => { Console.WriteLine(x.Name); });   Console.WriteLine("4、顯示索引為0元素的名稱：");   Console.WriteLine(lineNodes[0].Name);   Console.WriteLine("5、顯示編號為N4元素的名稱：");   Console.WriteLine(lineNodes["N4"].Name);   Console.WriteLine("6、清空");   lineNodes.Clear();   lineNodes.ForEach(x => { Console.WriteLine(x.Name); });   Console.ReadKey();  } } static class Utility {  public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)  {   foreach(var r in source)   {    action(r);   }  } } class LineNodeCollection : IEnumerable<LineNode> {  public IEnumerator<LineNode> GetEnumerator()  {   return new LineNodeEnumerator(this.firstLineNode);  }  IEnumerator IEnumerable.GetEnumerator()  {   return this.GetEnumerator();  }  public LineNode this[int index]  {   get   {    LineNode _lineNode= this.firstLineNode;    for (int i=0;i<=index;i++)    {     if (_lineNode != null)     {      if(i<index)      {       _lineNode = _lineNode.Next;       continue;      }      else      {       return _lineNode;      }     }     else break;    }    throw new IndexOutOfRangeException("超出集合索引范圍");   }  }  public LineNode this[string id]  {   get   {    LineNode _lineNode = this.firstLineNode;    for (int i = 0; i < this.Count; i++)    {     if(_lineNode.ID == id)     {      return _lineNode;     }      else     {      _lineNode = _lineNode.Next;     }    }    throw new IndexOutOfRangeException("未能在集合中找到該元素");   }  }  LineNode firstLineNode;  LineNode lastLineNode;  public void Add(LineNode lineNode)  {   this.Count++;   if(this.firstLineNode == null)   {    this.firstLineNode = lineNode;   }   else   {    if (this.firstLineNode.Next == null)    {     lineNode.Previous = this.firstLineNode;     this.firstLineNode.Next = lineNode;     this.lastLineNode = this.firstLineNode.Next;    }    else    {     lineNode.Previous = this.lastLineNode;     this.lastLineNode.Next = lineNode;     this.lastLineNode = this.lastLineNode.Next;    }   }  }  public int Count  {   private set;get;  }  public int IndexOf(string id)  {   LineNode _lineNode = this.firstLineNode;   for (int i = 0; i < this.Count; i++)   {    if (_lineNode.ID == id)    {     return i;    }    else    {     _lineNode = _lineNode.Next;    }   }   throw new IndexOutOfRangeException("未能在集合中找到該元素");  }  public void Clear()  {   this.firstLineNode = null;   this.lastLineNode = null;   this.Count = 0;   this.GetEnumerator().Reset();  }  public void RemoveAt(int index)  {   if (this.Count < index) throw new InvalidOperationException("超出集合索引范圍");   LineNode _currentLineNode = this[index];   if (_currentLineNode.Previous == null)   {    _currentLineNode = _currentLineNode.Next;    this.firstLineNode = _currentLineNode;   }   else    {     LineNode _lineNode = this.firstLineNode;    for (int i = 0; i <= index - 1; i++)    {     if (i < index - 1)     {      _lineNode = _lineNode.Next;      continue;     }     if (i == index - 1)     {      if (_currentLineNode.Next != null)      {       _lineNode.Next = _lineNode.Next.Next;      }      else      {       this.lastLineNode = _lineNode;       _lineNode.Next = null;      }      break;     }    }   }   this.Count--;  }  public void Remove(string id)  {   int _index = this.IndexOf(id);   this.RemoveAt(_index);  }  public LineNode TopLineNode { get { return this.firstLineNode; } }  public LineNode LastLineNode { get { return this.lastLineNode; } } } class LineNodeEnumerator : IEnumerator<LineNode> {  LineNode topLineNode;  public LineNodeEnumerator(LineNode topLineNode)  {   this.topLineNode = topLineNode;  }  public LineNode Current  {   get   {    return this.lineNode;   }  }  object IEnumerator.Current  {   get   {    return this.Current;   }  }  public void Dispose()  {   this.lineNode = null;  }  LineNode lineNode;  public bool MoveNext()  {   if(this.lineNode == null)   {    this.lineNode = this.topLineNode;    if (this.lineNode == null) return false;    if (this.lineNode.Next == null)     return false;    else     return true;   }   else   {    if(this.lineNode.Next !=null)    {     this.lineNode = this.lineNode.Next;     return true;    }    return false;   }  }  public void Reset()  {   this.lineNode = null;  } } class LineNode {  public LineNode(string id)  {   this.ID = id;  }  public string ID { private set; get; }  public string Name {set; get; }  public LineNode Next { set; get; }  public LineNode Previous { set; get; } }}