IEnumerator.MoveNext 方法


將列舉值往前推至下集合中的下一個項目。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



如果列舉值成功前移至下一個項目,則為 true;如果列舉值超過集合的結尾,則為 falsetrue if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the collection.


建立列舉值之後,集合已修改。The collection was modified after the enumerator was created.


下列程式碼範例示範 IEnumerator 自訂集合的介面實作為介面。The following code example demonstrates the implementation of the IEnumerator interfaces for a custom collection. 在此範例中, MoveNext 不會明確呼叫,但是它會實作為支援使用 foreach for each Visual Basic) 中的 (。In this example, MoveNext is not explicitly called, but it is implemented to support the use of foreach (for each in Visual Basic). 這個程式碼範例是介面較大範例的一部分 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


在建立列舉值之後或 Reset 呼叫方法之後,列舉值會放置在集合的第一個專案之前,而第一次呼叫 MoveNext 方法會將列舉值移至集合的第一個元素。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.

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,然後 MoveNext 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. 當列舉值位於這個位置時,後續呼叫 MoveNext 也會傳回, false 直到呼叫為止 ResetWhen the enumerator is at this position, subsequent calls to MoveNext also return false until Reset is called.

如果對集合進行了變更,例如加入、修改或刪除專案,則的行為未 MoveNext 定義。If changes are made to the collection, such as adding, modifying, or deleting elements, the behavior of MoveNext is undefined.