【数据结构】 List 简单实现

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public class XList<T> : IEnumerable, IEnumerator  {      #region List 简单实现        /// <summary>      /// 存储数据 数组      /// </summary>      private T[] _items;        /// <summary>      /// 默认容量      /// </summary>      private const int DefaultLength = 4;        /// <summary>      /// 插入最后一个元素索引（初始化时没有元素，所以为 -1）      /// </summary>      private int _lastIndex = -1;        /// <summary>      /// 无参构造      /// </summary>      public XList()      {          _items = new T[DefaultLength];      }        /// <summary>      /// 带初始容量的构造      /// </summary>      /// <param name="length"></param>      public XList(int length)      {          if (length <= 0)          {              throw new Exception("长度必须大于0");          }          _items = new T[length];      }        /// <summary>      /// 索引器      /// </summary>      /// <param name="index"></param>      /// <returns></returns>      public T this[int index]      {          get          {              CheckIndex(index); // 验证索引越界              return _items[index];          }          set { Insert(index, value); }      }        /// <summary>      /// 添加元素      /// </summary>      /// <param name="t"></param>      public void Add(T t)      {          Insert(_lastIndex + 1, t);      }        /// <summary>      /// 插入元素      /// </summary>      /// <param name="index"></param>      /// <param name="t"></param>      public void Insert(int index, T t)      {          if (index < 0)          {              throw new Exception("索引不能小于0");          }          KeepCapacity();          if (index <= _lastIndex) // 插入位置已有元素          {              T[] temp = new T[Capacity];              for (int i = 0; i < index; i++)              {                  temp[i] = _items[i];              }              temp[index] = t;              for (int i = index; i <= _lastIndex; i++)              {                  temp[i + 1] = _items[i];              }              _items = temp;<br>　　　　　　　　　 _lastIndex++;          }          else if (index == _lastIndex + 1) // 在末尾插入          {              _items[++_lastIndex] = t;          }          else          {              throw new Exception("索引越界");          }      }        /// <summary>      /// 按 索引 移除元素      /// </summary>      /// <param name="index"></param>      public void Remove(int index)      {          CheckIndex(index);          if (index != _lastIndex) // 移除元素不是最后一个元素          {              T[] temp = _items;              for (int i = index; i < _lastIndex; i++)              {                  temp[i] = _items[i + 1];              }              _items = temp;          }          // 移除元素是最后一个元素，不做处理          _lastIndex--;      }        /// <summary>      /// 集合存储元素数量      /// </summary>      /// <returns></returns>      public int Count()      {          return _lastIndex + 1;      }        /// <summary>      /// 清空集合      /// </summary>      public void Clear()      {          _lastIndex = -1;      }        /// <summary>      /// 集合 容量      /// </summary>      private int Capacity      {          get          {              if (_items != null)              {                  return _items.Length;              }              return -1;          }      }        /// <summary>      /// 保证容量充足，如果数组容量不够就重置大小，容量扩大一倍      /// </summary>      private void KeepCapacity()      {          if (Capacity == -1) // 数组为 null 的情况          {              _items = new T[DefaultLength];              return;          }          if (_lastIndex < Capacity - 1) // 容量足够          {              return;          }          // 容量不够          int length = Capacity * 2;          T[] temp = new T[length];          for (int i = 0; i < this.Capacity; i++)          {              temp[i] = _items[i];          }          _items = temp;      }        /// <summary>      /// 检查索引越界的情况      /// </summary>      /// <param name="index"></param>      private void CheckIndex(int index)      {          if (index > _lastIndex)          {              throw new Exception("索引越界");          }      }        #endregion        #region 实现枚举        #region IEnumerable 成员        public IEnumerator GetEnumerator()      {          return this;      }        #endregion        #region IEnumerator 成员        private int _position = -1;        public object Current      {          get { return _items[_position]; }      }        public bool MoveNext()      {          if (_position < _lastIndex)          {              _position++;              return true;          }          return false;      }        public void Reset()      {          _position = -1;      }        #endregion        #endregion  }

算是比较简单的 List 的实现，暂时先这样，有些地方还得完善，
知识点 ： 索引器，枚举器，其他的都比较简单