IEnumerator 介面

參考

定義

命名空間:: System.Collections

組件:: System.Runtime.dll

組件:: mscorlib.dll

組件:: netstandard.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

支援非泛型集合上的簡單反覆專案。

public interface class IEnumerator

public interface IEnumerator

[System.Runtime.InteropServices.Guid("496B0ABF-CDEE-11d3-88E8-00902754C43A")]
public interface IEnumerator

[System.Runtime.InteropServices.Guid("496B0ABF-CDEE-11d3-88E8-00902754C43A")]
[System.Runtime.InteropServices.ComVisible(true)]
public interface IEnumerator

type IEnumerator = interface

[<System.Runtime.InteropServices.Guid("496B0ABF-CDEE-11d3-88E8-00902754C43A")>]
type IEnumerator = interface

[<System.Runtime.InteropServices.Guid("496B0ABF-CDEE-11d3-88E8-00902754C43A")>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type IEnumerator = interface

Public Interface IEnumerator

衍生: Microsoft.Extensions.Primitives.StringTokenizer.Enumerator

Microsoft.Extensions.Primitives.StringValues.Enumerator

Microsoft.VisualBasic.Compatibility.VB6.BindingCollectionEnumerator

Microsoft.VisualBasic.Vsa.VsaItemsEnumerator

Microsoft.VisualC.StlClr.DequeEnumerator<TValue>

更多…

屬性: GuidAttribute ComVisibleAttribute

範例

下列程式代碼範例示範自定義集合 IEnumerable 和 IEnumerator 介面的實作。在此範例中，不會明確呼叫這些介面的成員，但會實作這些介面，以支援在Visual Basic中使用 foreach （for each）逐一查看集合。

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

備註

IEnumerator 是所有非泛型列舉值的基底介面。其泛型對等專案是 System.Collections.Generic.IEnumerator<T> 介面。

C# 語言的 foreach 語句（在 Visual Basic 中for each）會隱藏列舉值的複雜性。因此，建議使用 foreach，而不是直接操作列舉值。

列舉值可用來讀取集合中的數據，但無法用來修改基礎集合。

Reset 方法適用於 COM 互操作性，不需要完全實作;相反地，實作者可以擲回 NotSupportedException。

一開始，列舉值會放在集合中的第一個專案之前。您必須先呼叫 MoveNext 方法，才能將列舉值移至集合的第一個專案，再讀取 Current的值;否則，Current 未定義。

Current 會傳回相同的物件，直到呼叫 MoveNext 或 Reset 為止。 MoveNext 會將 Current 設定為下一個專案。

如果 MoveNext 傳遞集合結尾，則列舉值位於集合的最後一個項目之後，MoveNext 傳回 false。當列舉值位於這個位置時，後續呼叫 MoveNext 也會傳回 false。如果最後一次呼叫傳回 MoveNextfalse，則 Current 未定義。

若要再次將 Current 設定為集合的第一個專案，您可以呼叫 Reset，如果已實作，後面接著 MoveNext。如果未實作 Reset，您必須建立新的列舉值實例，才能返回集合的第一個專案。

如果對集合進行變更，例如新增、修改或刪除專案，列舉值的行為是未定義的。

列舉值沒有集合的獨佔存取權;因此，透過集合列舉本質上不是安全線程的程式。即使集合同步處理，其他線程仍然可以修改集合，這會導致列舉值擲回例外狀況。若要保證列舉期間的線程安全性，您可以在整個列舉期間鎖定集合，或攔截其他線程所做的變更所產生的例外狀況。

屬性

Current

取得集合中位於列舉值目前位置的專案。

方法

MoveNext()	將列舉值前進至集合的下一個專案。
Reset()	將列舉值設定為其初始位置，也就是集合中第一個專案之前。

適用於

共用方式為

IEnumerator 介面

定義

範例

備註

屬性

方法

適用於

另請參閱

其他資源