IEnumerable

IEnumerable

                                      

二.IEnumerable和IEnumerable
   主要实现  public IEnumerator GetEnumerator()
 
C# 1.0中的foreach

没有迭代器的时候，创建一个可用于foreach的集合（C# 1.0）:

 public class MyCollection : IEnumerable
 {
  public MyEnumerator GetEnumerator()
  {
   return new MyEnumerator(this);
  }
  public class MyEnumerator : IEnumerator
  {
   public void Reset(){...}
   public bool MoveNext(){...}
   public int Current{ get{...} }
   object IEnumerator.Current{ get{...} }
  }
 }

对集合使用foreach语句：
  foreach(int i in col){...}

 相单于：
 IEnumerator etor = ((IEnumerable)col).GetEnumerator();
 try
 {
  while(etor.MoveNext())
  {
   ElementType clem (ElementType)etor.Current;
   ...;
  }
 }
 finally{(IDisposable)enumerator).Dispose();}

C# 2.0 中的迭代器

使用迭代器创建于foreach的集合（C# 2.0）：

 public class Stack :IEnumerable
 {
  T[] items;
  int count;
  public void Push(T data){...}
  public T Pop(){...}
  public IEnumerator GetEnumerator()
  {
   for(int i=count-1;i>=0;--i)
   {
     yield return items[i];
   }
  }
 }

 使用foreach语句：

 Stack stack = new Stack ();
 foreach(int i in statck){...}

2006年02月(5)

数据源转成IEnumerable类型 //将数据源中的数据都转换为IEnumerable类型,用作数据绑定 //其中_dataSource为数据源,DataMember为要找的数据名称   protected virtual IEnumerable GetDataSource()   {        if(_dataSource == null)    {     return null;    }        IEnumerable resolvedDataSource = _dataSource as IEnumerable;    if(resolvedDataSource != null)    {     return resolvedDataSource;    }    IListSource listSource = _dataSource as IListSource;    if(listSource != null)    {     IList memberList = listSource.GetList();          int i = memberList.Count;          if(listSource.ContainsListCollection == false)     {      return (IEnumerable)memberList;     }     ITypedList typedMemberList = memberList as ITypedList;     if(typedMemberList != null)     {      PropertyDescriptorCollection propDescs = typedMemberList.GetItemProperties(new PropertyDescriptor[0]);      PropertyDescriptor memberProperty = null;      if((propDescs != null) && (propDescs.Count!=0))      {       string dataMember = DataMember;       if(dataMember.Length == 0)       {        memberProperty = propDescs[0];       }       else       {        memberProperty = propDescs.Find(dataMember,true);       }       if(memberProperty != null)       {        object listRow = memberList[0];        object list = memberProperty.GetValue(listRow);        if(list is IEnumerable)        {         return (IEnumerable)list;        }       }       throw new Exception("no Datamember.");      }            throw new Exception("no datamember.");     }    }    return null;   }