IEnumerator IEnumerator IEnumerator IEnumerator Interface

Definition

支持对非泛型集合的简单迭代。 Supports a simple iteration over a non-generic collection.

public interface class IEnumerator
[System.Runtime.InteropServices.ComVisible(true)]
[System.Runtime.InteropServices.Guid("496B0ABF-CDEE-11d3-88E8-00902754C43A")]
public interface IEnumerator
type IEnumerator = interface
Public Interface IEnumerator
Derived
Attributes

Examples

下面的代码示例演示如何实现IEnumerableIEnumerator为自定义集合的接口。The following code example demonstrates the implementation of the IEnumerable and IEnumerator interfaces for a custom collection. 在此示例中,没有显式调用这些接口的成员,但它们实现以支持使用foreach(for each在 Visual Basic 中) 以循环访问集合。In this example, members of these interfaces are not explicitly called, but they are implemented to support the use of foreach (for each in Visual Basic) to iterate through the collection.

using System;
using System.Collections;

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

    public string firstName;
    public string lastName;
}

// Collection of Person objects. This class
// implements IEnumerable so that it can be used
// with ForEach syntax.
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];
        }
    }

// Implementation for the GetEnumerator method.
    IEnumerator IEnumerable.GetEnumerator()
    {
       return (IEnumerator) GetEnumerator();
    }

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

// When you implement IEnumerable, you must also implement IEnumerator.
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;
    }

    object IEnumerator.Current
    {
        get
        {
            return Current;
        }
    }

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

class App
{
    static void Main()
    {
        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)
            Console.WriteLine(p.firstName + " " + p.lastName);

    }
}

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

' Simple business object.
Public Class Person

    Public Sub New(ByVal fName As String, ByVal lName As String)
        Me.firstName = fName
        Me.lastName = lName
    End Sub


    Public firstName As String
    Public lastName As String
End Class

' Collection of Person objects, which implements IEnumerable so that
' it can be used with ForEach syntax.
Public Class People
    Implements IEnumerable

    Private _people() As Person

    Public Sub New(ByVal pArray() As Person)
        _people = New Person(pArray.Length - 1) {}

        Dim i As Integer
        For i = 0 To pArray.Length - 1
            _people(i) = pArray(i)
        Next i
    End Sub

    ' Implementation of GetEnumerator.
    Public Function GetEnumerator() As IEnumerator _
      Implements IEnumerable.GetEnumerator

        Return New PeopleEnum(_people)
    End Function

End Class

' When you implement IEnumerable, you must also implement IEnumerator.
Public Class PeopleEnum
    Implements IEnumerator

    Public _people() As Person

    ' Enumerators are positioned before the first element
    ' until the first MoveNext() call.
    Dim position As Integer = -1

    Public Sub New(ByVal list() As Person)
        _people = list
    End Sub

    Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
        position = position + 1
        Return (position < _people.Length)
    End Function

    Public Sub Reset() Implements IEnumerator.Reset
        position = -1
    End Sub

    Public ReadOnly Property Current() As Object Implements IEnumerator.Current
        Get
            Try
                Return _people(position)
            Catch ex As IndexOutOfRangeException
                Throw New InvalidOperationException()
            End Try
        End Get
    End Property
End Class

Class App
    Shared Sub Main()
        Dim peopleArray() As Person = { _
            New Person("John", "Smith"), _
            New Person("Jim", "Johnson"), _
            New Person("Sue", "Rabon")}

        Dim peopleList As New People(peopleArray)
        Dim p As Person
        For Each p In peopleList
            Console.WriteLine(p.firstName + " " + p.lastName)
        Next

    End Sub
End Class

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

Remarks

IEnumerator 是所有非泛型枚举器的基接口。IEnumerator is the base interface for all non-generic enumerators. 其泛型等效项是System.Collections.Generic.IEnumerator<T>接口。Its generic equivalent is the System.Collections.Generic.IEnumerator<T> interface.

C# 语言的 foreach 语句(在 Visual Basic 中为 for each)隐藏了枚举数的复杂性。The foreach statement of the C# language (for each in Visual Basic) hides the complexity of the enumerators. 因此,使用foreach建议而不是直接操作枚举器。Therefore, using foreach is recommended instead of directly manipulating the enumerator.

枚举器可用于读取集合中的数据,但不能用于修改基础集合。Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

Reset方法提供的 COM 互操作性,并且无需将其完全实现; 相反,实施者可能会引发NotSupportedExceptionThe Reset method is provided for COM interoperability and does not need to be fully implemented; instead, the implementer can throw a NotSupportedException.

最初,枚举数定位在集合中第一个元素的前面。Initially, the enumerator is positioned before the first element in the collection. 必须调用MoveNext方法将枚举数前移到集合,然后再读取的值的第一个元素Current; 否则为Current是不确定的。You must call the MoveNext method to advance the enumerator to the first element of the collection before reading the value of Current; otherwise, Current is undefined.

在调用 CurrentMoveNext 之前,Reset 返回同一对象。Current returns the same object until either MoveNext or Reset is called. MoveNextCurrent 设置为下一个元素。MoveNext sets Current to the next element.

如果MoveNext越过集合,枚举器的末尾放置在集合中的最后一个元素的后面和MoveNext返回falseIf MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. 当枚举数位于此位置上,对后续调用MoveNext还返回falseWhen the enumerator is at this position, subsequent calls to MoveNext also return false. 如果最后一次调用到MoveNext返回falseCurrent是不确定的。If the last call to MoveNext returned false, Current is undefined.

若要设置Current再次集合的第一个元素,可以调用Reset,如果实现它后后, 跟MoveNextTo set Current to the first element of the collection again, you can call Reset, if it’s implemented, followed by MoveNext. 如果Reset是未实现,必须创建新的枚举数实例以返回到集合的第一个元素。If Reset is not implemented, you must create a new enumerator instance to return to the first element of the collection.

如果更改到集合中,如添加、 修改或删除元素,枚举器的行为未定义。If changes are made to the collection, such as adding, modifying, or deleting elements, the behavior of the enumerator is undefined.

枚举数没有对集合的独占访问权;因此,从头到尾对一个集合进行枚举在本质上不是一个线程安全的过程。The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. 即使某个集合已同步,其他线程仍可以修改该集合,这会导致枚举数引发异常。Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. 若要确保枚举过程中的线程安全性,可以在整个枚举期间锁定集合,或者捕获由其他线程进行的更改所导致的异常。To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

Properties

Current Current Current Current

获取集合中位于枚举数当前位置的元素。 Gets the element in the collection at the current position of the enumerator.

Methods

MoveNext() MoveNext() MoveNext() MoveNext()

将枚举数推进到集合的下一个元素。 Advances the enumerator to the next element of the collection.

Reset() Reset() Reset() Reset()

将枚举数设置为其初始位置,该位置位于集合中第一个元素之前。 Sets the enumerator to its initial position, which is before the first element in the collection.

Applies to

See Also