IEnumerator.MoveNext メソッド


列挙子をコレクションの次の要素に進めます。Advances the enumerator to the next element of the collection.

 bool MoveNext();
public bool MoveNext ();
abstract member MoveNext : unit -> bool
Public Function MoveNext () As Boolean



列挙子が次の要素に正常に進んだ場合は true。列挙子がコレクションの末尾を越えた場合は falsetrue if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the collection.


コレクションは、列挙子の作成後に変更されました。The collection was modified after the enumerator was created.

次のコード例は、カスタムコレクションのインターフェイスの実装を示して IEnumerator います。The following code example demonstrates the implementation of the IEnumerator interfaces for a custom collection. この例で MoveNext は、は明示的に呼び出されませんが、(Visual Basic) の使用をサポートするように実装されてい foreach for each ます。In this example, MoveNext 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、インターフェイスのより大きな例の一部です IEnumeratorThis code example is part of a larger example for the IEnumerator interface.

// 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()
        return (position < _people.Length);

    public void Reset()
        position = -1;

    object IEnumerator.Current
            return Current;

    public Person Current
                return _people[position];
            catch (IndexOutOfRangeException)
                throw new InvalidOperationException();
' 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
                Return _people(position)
            Catch ex As IndexOutOfRangeException
                Throw New InvalidOperationException()
            End Try
        End Get
    End Property
End Class


列挙子が作成された後 Reset 、またはメソッドが呼び出された後、列挙子はコレクションの最初の要素の前に配置され、メソッドの最初の呼び出しでは、 MoveNext 列挙子をコレクションの最初の要素に移動します。After an enumerator is created or after the Reset method is called, an enumerator is positioned before the first element of the collection, and the first call to the MoveNext method moves the enumerator over the first element of the collection.

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、後続のを呼び出すと、 MoveNext false が呼び出されるまでが返され Reset ます。When the enumerator is at this position, subsequent calls to MoveNext also return false until Reset is called.

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、の動作 MoveNext 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 MoveNext is undefined.