c#的IList,IEnumerable和IEnumerator

IList 是 ICollection 接口的子代，并且是所有非泛型列表的基接口。IList 实现有三种类别：只读、固定大小和可变大小。无法修改只读 IList。固定大小的 IList 不允许添加或移除元素，但允许修改现有元素。可变大小的 IList 允许添加、移除和修改元素。

 

下面的示例演示创建一个简单列表——固定大小列表的 IList 接口的实现。

 

class SimpleList : IList
{
   private object[] _contents = new object[8];
   private int _count;

   public SimpleList()
   {
      _count = 0;
   }

   // IList Members
   public int Add(object value)
   {
      if (_count < _contents.Length)
      {
         _contents[_count] = value;
         _count++;

         return (_count - 1);
      }
      else
      {
         return -1;
      }
   }

   public void Clear()
   {
      _count = 0;
   }

   public bool Contains(object value)
   {
      bool inList = false;
      for (int i = 0; i < Count; i++)
      {
         if (_contents[i] == value)
         {
            inList = true;
            break;
         }
      }
      return inList;
   }

   public int IndexOf(object value)
   {
      int itemIndex = -1;
      for (int i = 0; i < Count; i++)
      {
         if (_contents[i] == value)
         {
            itemIndex = i;
            break;
         }
      }
      return itemIndex;
   }

   public void Insert(int index, object value)
   {
      if ((_count + 1 <= _contents.Length) && (index < Count) && (index >= 0))
      {
         _count++;

         for (int i = Count - 1; i > index; i--)
         {
            _contents[i] = _contents[i - 1];
         }
         _contents[index] = value;
      }
   }

   public bool IsFixedSize
   {
      get
      {
         return true;
      }
   }

   public bool IsReadOnly
   {
      get
      {
         return false;
      }
   }

   public void Remove(object value)
   {
      RemoveAt(IndexOf(value));
   }

   public void RemoveAt(int index)
   {
      if ((index >= 0) && (index < Count))
      {
         for (int i = index; i < Count - 1; i++)
         {
            _contents[i] = _contents[i + 1];
         }
         _count--;
      }
   }

   public object this[int index]
   {
      get
      {
         return _contents[index];
      }
      set
      {
         _contents[index] = value;
      }
   }

   // ICollection Members

   public void CopyTo(Array array, int index)
   {
      int j = index;
      for (int i = 0; i < Count; i++)
      {
         array.SetValue(_contents[i], j);
         j++;
      }
   }

   public int Count
   {
      get
      {
         return _count;
      }
   }

   public bool IsSynchronized
   {
      get
      {
         return false;
      }
   }

   // Return the current instance since the underlying store is not
   // publicly available.
   public object SyncRoot
   {
      get
      {
         return this;
      }
   }

   // IEnumerable Members

   public IEnumerator GetEnumerator()
   {
      // Refer to the IEnumerator documentation for an example of
      // implementing an enumerator.
      throw new Exception("The method or operation is not implemented.");
   }

   public void PrintContents(System.Windows.Controls.TextBlock outputBlock)
   {
      outputBlock.Text += String.Format("List has a capacity of {0} and currently has {1} elements.", _contents.Length, _count) + "\n";
      outputBlock.Text += "List contents:";
      for (int i = 0; i < Count; i++)
      {
         outputBlock.Text += String.Format(" {0}", _contents[i]);
      }
      outputBlock.Text += "\n";
   }
}

 

 

下面的代码示例演示如何实现自定义集合的 IEnumerable 和 IEnumerator 接口。在此示例中，没有显式调用这些接口的成员，但实现了它们，以便支持使用 foreach循环访问该集合。

using System;
using System.Collections;

public class Person
{
   public Person(string fName, string lName)
   {
      this.firstName = fName;
      this.lastName = lName;
   }

   public string firstName;
   public string lastName;
}

public class People : IEnumerable
{
   private Person[] _people;
   public People(Person[] pArray)
   {
      _people = new Person[pArray.Length];

      for (int i = 0; i < pArray.Length; i++)
      {
         _people[i] = pArray[i];
      }
   }

   public IEnumerator GetEnumerator()
   {
      return new PeopleEnum(_people);
   }
}

public class PeopleEnum : IEnumerator
{
   public Person[] _people;

   // Enumerators are positioned before the first element
   // until the first MoveNext() call.
   int position = -1;

   public PeopleEnum(Person[] list)
   {
      _people = list;
   }

   public bool MoveNext()
   {
      position++;
      return (position < _people.Length);
   }

   public void Reset()
   {
      position = -1;
   }

   public object Current
   {
      get
      {
         try
         {
            return _people[position];
         }
         catch (IndexOutOfRangeException)
         {
            throw new InvalidOperationException();
         }
      }
   }
}

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      Person[] peopleArray = new Person[3]
        {
            new Person("John", "Smith"),
            new Person("Jim", "Johnson"),
            new Person("Sue", "Rabon"),
        };

      People peopleList = new People(peopleArray);
      foreach (Person p in peopleList)
         outputBlock.Text += p.firstName + " " + p.lastName + "\n";

   }
}

/* This code produces output similar to the following:
 * 
 * John Smith
 * Jim Johnson
 * Sue Rabon
 * 
 */