IEnumerable.GetEnumerator メソッド

定義

コレクションを反復処理する列挙子を返します。Returns an enumerator that iterates through a collection.

public:
 System::Collections::IEnumerator ^ GetEnumerator();
public System.Collections.IEnumerator GetEnumerator ();
abstract member GetEnumerator : unit -> System.Collections.IEnumerator
Public Function GetEnumerator () As IEnumerator

戻り値

コレクションを反復処理するために使用できる IEnumerator オブジェクト。An IEnumerator object that can be used to iterate through the collection.

次のコード例は、カスタムコレクションのIEnumerableインターフェイスの実装を示しています。The following code example demonstrates the implementation of the IEnumerable interfaces for a custom collection. この例ではGetEnumerator 、は明示的に呼び出されませんが、(For Each Visual Basic) foreachの使用をサポートするように実装されています。In this example, GetEnumerator is not explicitly called, but it is implemented to support the use of foreach (For Each in Visual Basic). このコード例は、 IEnumerableインターフェイスのより大きな例の一部です。This code example is part of a larger example for the IEnumerable interface.

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

注釈

C# 言語の foreach ステートメント (Visual Basic の場合は For Each) を使用することで列挙子の複雑さを回避できます。The foreach statement of the C# language (For Each in Visual Basic) hides the complexity of the enumerators. したがって、列挙子を直接操作するのではなく、foreach を使用することをお勧めします。Therefore, using foreach is recommended, instead of directly manipulating the enumerator.

列挙子を使用すると、コレクション内のデータを読み取ることができますが、基になるコレクションを変更することはできません。Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

最初に、列挙子はコレクション内の 1 番目の要素の前に位置付けられます。Initially, the enumerator is positioned before the first element in the collection. Reset メソッドは、この位置に列挙子を戻します。The Reset method also brings the enumerator back to this position. この位置では、Current プロパティは定義されていません。At this position, the Current property is undefined. そのため、Current の値を読み取る前に、MoveNext メソッドを呼び出し、列挙子をコレクションの最初の要素に進める必要があります。Therefore, you must call the MoveNext method to advance the enumerator to the first element of the collection before reading the value of Current.

Current は、MoveNext または Reset が呼び出されるまでは同じオブジェクトを返します。Current returns the same object until either MoveNext or Reset is called. MoveNext は、Current を次の要素に設定します。MoveNext sets Current to the next element.

MoveNext がコレクションの末尾を通過した場合、列挙子がコレクション内の最後の要素の後に配置され、MoveNextfalse を返します。If MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. 列挙子がこの位置にある場合、後続の MoveNext 呼び出しも false を返します。When the enumerator is at this position, subsequent calls to MoveNext also return false. 最後の MoveNext 呼び出しが false を返す場合、Current は定義されていません。If the last call to MoveNext returns false, Current is undefined. Current をコレクションの最初の要素にもう一度設定するには、Reset を呼び出してから MoveNext を呼び出します。To set Current to the first element of the collection again, you can call Reset followed by MoveNext.

要素の追加、変更、削除などの変更がコレクションに対して行われた場合、列挙子の動作は未定義になります。If changes are made to the collection, such as adding, modifying, or deleting elements, the behavior of the enumerator is undefined.

列挙子にはコレクションへの排他アクセス権限はないため、コレクションの列挙処理は本質的にスレッド セーフな処理ではありません。The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. 列挙処理でスレッド セーフを確保するために、列挙処理が終わるまでコレクションをロックできます。To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. コレクションに対し複数のスレッドがアクセスして読み取りや書き込みを行うことができるようにするには、独自に同期化を実装する必要があります。To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

適用対象

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