IEnumerator<T> Interface

Definition

支援對泛型集合執行簡單的反覆查看。Supports a simple iteration over a generic collection.

generic <typename T>
public interface class IEnumerator : IDisposable, System::Collections::IEnumerator
public interface IEnumerator<out T> : IDisposable, System.Collections.IEnumerator
public interface IEnumerator<T> : IDisposable, System.Collections.IEnumerator
type IEnumerator<'T> = interface
    interface IEnumerator
    interface IDisposable
type IEnumerator<'T> = interface
    interface IDisposable
    interface IEnumerator
Public Interface IEnumerator(Of Out T)
Implements IDisposable, IEnumerator
Public Interface IEnumerator(Of T)
Implements IDisposable, IEnumerator

Type Parameters

T

要列舉之物件的類型。The type of objects to enumerate.

This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
Derived
Implements

Examples

下列範例顯示自訂物件的集合類別之 IEnumerator<T> 介面的執行。The following example shows an implementation of the IEnumerator<T> interface for a collection class of custom objects. 自訂物件是 Box類型的實例,而集合類別則 BoxCollectionThe custom object is an instance of the type Box, and the collection class is BoxCollection. 這個程式碼範例是提供給 ICollection<T> 介面之較大範例的一部分。This code example is part of a larger example provided for the ICollection<T> interface.


// Defines the enumerator for the Boxes collection.
// (Some prefer this class nested in the collection class.)
public class BoxEnumerator : IEnumerator<Box>
{
    private BoxCollection _collection;
    private int curIndex;
    private Box curBox;

    public BoxEnumerator(BoxCollection collection)
    {
        _collection = collection;
        curIndex = -1;
        curBox = default(Box);
    }

    public bool MoveNext()
    {
        //Avoids going beyond the end of the collection.
        if (++curIndex >= _collection.Count)
        {
            return false;
        }
        else
        {
            // Set current box to next item in collection.
            curBox = _collection[curIndex];
        }
        return true;
    }

    public void Reset() { curIndex = -1; }

    void IDisposable.Dispose() { }

    public Box Current
    {
        get { return curBox; }
    }

    object IEnumerator.Current
    {
        get { return Current; }
    }
}
' Defines the enumerator for the Boxes collection.
' (Some prefer this class nested in the collection class.)
Public Class BoxEnumerator
    Implements IEnumerator(Of Box)
    Private _collection As BoxCollection
    Private curIndex As Integer
    Private curBox As Box


    Public Sub New(ByVal collection As BoxCollection)
        MyBase.New()
        _collection = collection
        curIndex = -1
        curBox = Nothing

    End Sub

    Private Property Box As Box
    Public Function MoveNext() As Boolean _
        Implements IEnumerator(Of Box).MoveNext
        curIndex = curIndex + 1
        If curIndex = _collection.Count Then
            ' Avoids going beyond the end of the collection.
            Return False
        Else
            'Set current box to next item in collection.
            curBox = _collection(curIndex)
        End If
        Return True
    End Function

    Public Sub Reset() _
        Implements IEnumerator(Of Box).Reset
        curIndex = -1
    End Sub

    Public Sub Dispose() _
        Implements IEnumerator(Of Box).Dispose

    End Sub

    Public ReadOnly Property Current() As Box _
        Implements IEnumerator(Of Box).Current

        Get
            If curBox Is Nothing Then
                Throw New InvalidOperationException()
            End If

            Return curBox
        End Get
    End Property

    Private ReadOnly Property Current1() As Object _
        Implements IEnumerator.Current

        Get
            Return Me.Current
        End Get
    End Property
End Class

' Defines two boxes as equal if they have the same dimensions.
Public Class BoxSameDimensions
    Inherits EqualityComparer(Of Box)

    Public Overrides Function Equals(ByVal b1 As Box, ByVal b2 As Box) As Boolean
        If b1.Height = b2.Height And b1.Length = b2.Length And b1.Width = b2.Width Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Overrides Function GetHashCode(ByVal bx As Box) As Integer
        Dim hCode As Integer = bx.Height ^ bx.Length ^ bx.Width
        Return hCode.GetHashCode()
    End Function
End Class

Remarks

IEnumerator<T> 是所有泛型枚舉器的基底介面。IEnumerator<T> is the base interface for all generic enumerators.

C#語言的 foreach 語句(for each 中C++的 For Each,Visual Basic 中的)會隱藏枚舉器的複雜性。The foreach statement of the C# language (for each in C++, For Each in Visual Basic) hides the complexity of the enumerators. 因此,建議您使用 foreach,而不要直接使用列舉值。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.

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. 在這個位置上,Current 並未定義。At this position, Current is undefined. 因此,在讀取 MoveNext 的值之前,必須呼叫 Current 以將列舉值前移至集合的第一個項目。Therefore, you must call MoveNext to advance the enumerator to the first element of the collection before reading the value of Current.

Current 會傳回相同的物件直到呼叫 MoveNextCurrent returns the same object until MoveNext 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. 您不能再次將 Current 設定為集合的第一個項目;您必須建立新的列舉值執行個體。You cannot set Current to the first element of the collection again; you must create a new enumerator instance instead.

Reset 方法是針對 COM 互通性所提供。The Reset method is provided for COM interoperability. 不一定需要實作為,相反地,實施者只會擲回 NotSupportedExceptionIt does not necessarily need to be implemented; instead, the implementer can simply throw a NotSupportedException. 不過,如果您選擇這麼做,則應該確定沒有任何呼叫端依賴 Reset 功能。However, if you choose to do this, you should make sure no callers are relying on the Reset functionality.

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. 若要確保列舉期間的執行緒安全性,您可以在整個列舉期間鎖定集合。To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. 若要讓多重執行緒能夠存取集合以便進行讀取和寫入,您必須實作自己的同步處理。To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

System.Collections.Generic 命名空間中集合的預設實作未同步處理。Default implementations of collections in the System.Collections.Generic namespace are not synchronized.

Notes to Implementers

若要執行此介面,必須實作為泛型 IEnumerator 介面。Implementing this interface requires implementing the nongeneric IEnumerator interface. MoveNext()Reset() 方法不會相依于 T,而且只會出現在非泛型介面上。The MoveNext() and Reset() methods do not depend on T, and appear only on the nongeneric interface. [Current] 屬性會出現在兩個介面上,且具有不同的傳回型別。The Current property appears on both interfaces, and has different return types. 將非泛型 Current 屬性實作為明確的介面執行。Implement the nongeneric Current property as an explicit interface implementation. 這可讓非泛型介面的任何取用者使用泛型介面。This allows any consumer of the nongeneric interface to consume the generic interface.

此外,IEnumerator<T> 會實 IDisposable,這會要求您執行 Dispose() 方法。In addition, IEnumerator<T> implements IDisposable, which requires you to implement the Dispose() method. 這可讓您在使用其他資源時,關閉資料庫連接或釋放檔案控制代碼或類似的作業。This enables you to close database connections or release file handles or similar operations when using other resources. 如果沒有其他資源可處置,請提供空的 Dispose() 執行。If there are no additional resources to dispose of, provide an empty Dispose() implementation.

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

Dispose()

執行與釋放或重設 Unmanaged 資源相關聯的應用程式定義工作。Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.

(Inherited from IDisposable)
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.

(Inherited from IEnumerator)
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.

(Inherited from IEnumerator)

Applies to

See also