IEnumerator.MoveNext 方法


讓列舉值前進到下一個集合元素。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



如果列舉值已成功前進到下一個元素,為 true;如果列舉值已跳過集合結尾,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如何執行自訂集合的 IEnumerator 介面。The following code example demonstrates the implementation of the IEnumerator interfaces for a custom collection. 在此範例中,不會明確呼叫 MoveNext,但會實作為支援在 Visual Basic 中使用 foreachfor each)。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 IEnumerator 介面之較大範例的一部分。This 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


在建立枚舉器或呼叫 Reset 方法之後,列舉值會位於集合的第一個專案之前,而第一次呼叫 MoveNext 方法會將枚舉器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,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 false 直到呼叫 Reset 為止。When 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、修改或刪除元素,則 MoveNext 的行為未定義。If changes are made to the collection, such as adding, modifying, or deleting elements, the behavior of MoveNext is undefined.