IEnumerator 接口

定义

支持对非泛型集合进行简单的迭代。

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

示例

下面的代码示例演示自定义集合的 IEnumerableIEnumerator 接口的实现。 在此示例中,不会显式调用这些接口的成员,但它们实现为支持使用 foreach(Visual Basic 中的for each)循环访问集合。

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.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

注解

IEnumerator 是所有非泛型枚举器的基本接口。 其泛型等效项是 System.Collections.Generic.IEnumerator<T> 接口。

C# 语言的 foreach 语句(在 Visual Basic 中for each)隐藏枚举器的复杂性。 因此,建议使用 foreach,而不是直接操作枚举器。

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。

为 COM 互操作性提供了 Reset 方法,无需完全实现;相反,实现者可以引发 NotSupportedException

最初,枚举器位于集合中的第一个元素之前。 在读取 Current值之前,必须调用 MoveNext 方法将枚举器前进到集合的第一个元素;否则,Current 未定义。

Current 返回相同的对象,直到调用 MoveNextResetMoveNextCurrent 设置为下一个元素。

如果 MoveNext 传递集合的末尾,则枚举器位于集合中的最后一个元素之后,MoveNext 返回 false。 当枚举器处于此位置时,对 MoveNext 的后续调用也会返回 false。 如果最后一次调用 MoveNext 返回 false,则 Current 未定义。

若要再次将 Current 设置为集合的第一个元素,可以调用 Reset(如果已实现)后跟 MoveNext。 如果未实现 Reset,则必须创建新的枚举器实例才能返回到集合的第一个元素。

如果对集合进行了更改(例如添加、修改或删除元素),则枚举器的行为是未定义的。

枚举器不具有对集合的独占访问权限;因此,通过集合进行枚举本质上不是线程安全的过程。 即使集合同步,其他线程仍可以修改集合,这会导致枚举器引发异常。 若要保证枚举期间的线程安全性,可以在整个枚举期间锁定集合,也可以捕获由其他线程所做的更改导致的异常。

属性

Current

获取集合中枚举器当前位置的元素。

方法

MoveNext()

将枚举器推进到集合的下一个元素。

Reset()

将枚举器设置为其初始位置,该位置位于集合中的第一个元素之前。

适用于

产品 版本
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

另请参阅