IEnumerator Interface

Definition

支援非泛型集合上的簡單反覆運算。Supports a simple iteration over a non-generic collection.

public interface class IEnumerator
public interface IEnumerator
[System.Runtime.InteropServices.Guid("496B0ABF-CDEE-11d3-88E8-00902754C43A")]
public interface 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

下列程式碼範例示範如何執行自訂集合的 IEnumerableIEnumerator 介面。The following code example demonstrates the implementation of the IEnumerable and IEnumerator interfaces for a custom collection. 在此範例中,不會明確呼叫這些介面的成員,但會將它們實作為支援使用 foreach (在 Visual Basic 中for each)來逐一查看集合。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.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 是所有非泛型枚舉器的基底介面。IEnumerator is the base interface for all non-generic enumerators. 它的泛型對等是 System.Collections.Generic.IEnumerator<T> 介面。Its generic equivalent is the System.Collections.Generic.IEnumerator<T> interface.

C# 語言的 foreach 陳述式 (在 Visual Basic 中為 for each) 會隱藏列舉值的複雜度。The foreach statement of the C# language (for each in Visual Basic) hides the complexity of the enumerators. 因此,建議使用 foreach,而不是直接操作列舉值。Therefore, using foreach is recommended instead of directly manipulating the enumerator.

列舉程式可以用來讀取集合中的資料,但是無法用來修改基礎集合。Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

Reset 方法是針對 COM 互通性所提供,而且不需要完全實作為;相反地,實施者可以擲回 NotSupportedExceptionThe Reset method is provided for COM interoperability and does not need to be fully implemented; instead, the implementer can throw a NotSupportedException.

一開始,列舉程式位在集合中的第一個項目之前。Initially, the enumerator is positioned before the first element in the collection. 您必須先呼叫 MoveNext 方法,將列舉值前移至集合的第一個元素,然後再讀取 Current的值;否則,Current 未定義。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.

Current 會傳回相同的物件直到呼叫 MoveNextResetCurrent returns the same object until either MoveNext or Reset is called. MoveNext 會將 Current 設定為下一個項目。MoveNext sets Current to the next element.

如果 MoveNext 傳遞集合的結尾,列舉值會放置在集合中的最後一個元素之後,而 MoveNext 會傳回 falseIf MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. 當列舉值在此位置時,MoveNext 的後續呼叫也會傳回 falseWhen the enumerator is at this position, subsequent calls to MoveNext also return false. 如果 MoveNext 傳回 false的最後一次呼叫,則 Current 未定義。If the last call to MoveNext returned false, Current is undefined.

若要再次將 Current 設定為集合的第一個專案,您可以呼叫 Reset(如果已實作為),後面接著 [MoveNext]。To set Current to the first element of the collection again, you can call Reset, if it's implemented, followed by MoveNext. 如果未執行 Reset,您必須建立新的列舉值實例,以返回集合的第一個元素。If Reset is not implemented, you must create a new enumerator instance to return to the first element of the collection.

如果對集合進行了變更,例如加入、修改或刪除元素,則列舉值的行為未定義。If changes are made to the collection, such as adding, modifying, or deleting elements, the behavior of the enumerator is undefined.

列舉程式沒有集合的獨佔存取權,因此,列舉集合內容本質上並不是安全的執行緒程序。The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. 即使集合經過同步化,其他的執行緒仍可修改該集合,使列舉值擲回例外狀況。Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. 若要保證列舉過程的執行緒安全,您可以在整個列舉過程中鎖定集合,或攔截由其他執行緒的變更所造成的例外狀況。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

取得集合中位於列舉值目前位置的元素。Gets the element in the collection at the current position of the enumerator.

Methods

MoveNext()

讓列舉值前進到下一個集合元素。Advances the enumerator to the next element of the collection.

Reset()

將列舉值設定為其初始位置,在集合的第一個元素之前。Sets the enumerator to its initial position, which is before the first element in the collection.

Applies to

See also