ArrayList.GetEnumerator 方法

定义

返回遍历 ArrayList 的枚举器。Returns an enumerator that iterates through the ArrayList.

重载

GetEnumerator()

返回用于整个 ArrayList 的枚举数。Returns an enumerator for the entire ArrayList.

GetEnumerator(Int32, Int32)

返回 ArrayList 中元素范围的枚举器。Returns an enumerator for a range of elements in the ArrayList.

GetEnumerator()

返回用于整个 ArrayList 的枚举数。Returns an enumerator for the entire ArrayList.

public:
 virtual System::Collections::IEnumerator ^ GetEnumerator();
public virtual System.Collections.IEnumerator GetEnumerator ();
abstract member GetEnumerator : unit -> System.Collections.IEnumerator
override this.GetEnumerator : unit -> System.Collections.IEnumerator
Public Overridable Function GetEnumerator () As IEnumerator

返回

IEnumerator

用于整个 ArrayListIEnumeratorAn IEnumerator for the entire ArrayList.

实现

示例

下面的示例获取的枚举器 ArrayList ,以及中某个元素范围的枚举器 ArrayListThe following example gets the enumerator for an ArrayList, and the enumerator for a range of elements in the ArrayList.

using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        ArrayList colors = new ArrayList();
        colors.Add("red");
        colors.Add("blue");
        colors.Add("green");
        colors.Add("yellow");
        colors.Add("beige");
        colors.Add("brown");
        colors.Add("magenta");
        colors.Add("purple");

        IEnumerator e = colors.GetEnumerator();
        while (e.MoveNext())
        {
            Object obj = e.Current;
            Console.WriteLine(obj);
        }

        Console.WriteLine();

        IEnumerator e2 = colors.GetEnumerator(2, 4);
        while (e2.MoveNext())
        {
            Object obj = e2.Current;
            Console.WriteLine(obj);
        }
    }
}

/* This code example produces
   the following ouput:
    red
    blue
    green
    yellow
    beige
    brown
    magenta
    purple

    green
    yellow
    beige
    brown
 */
Imports System.Collections

Class Program
    Private Shared Sub Main(ByVal args As String())
        Dim colors As New ArrayList()
        colors.Add("red")
        colors.Add("blue")
        colors.Add("green")
        colors.Add("yellow")
        colors.Add("beige")
        colors.Add("brown")
        colors.Add("magenta")
        colors.Add("purple")
        
        Dim e As IEnumerator = colors.GetEnumerator()
        While e.MoveNext()
            Dim obj As [Object] = e.Current
            Console.WriteLine(obj)
        End While
        
        Console.WriteLine()
        
        Dim e2 As IEnumerator = colors.GetEnumerator(2, 4)
        While e2.MoveNext()
            Dim obj As [Object] = e2.Current
            Console.WriteLine(obj)
        End While
    End Sub
End Class

' This code example produces
' the following ouput:
' red
' blue
' green
' yellow
' beige
' brown
' magenta
' purple
'
' green
' yellow
' beige
' brown
' 

注解

C# 语言的 foreach 语句(在 Visual Basic 中为 for each)隐藏了枚举数的复杂性。The foreach statement of the C# language (for each in Visual Basic) hides the complexity of the enumerators. 因此,建议使用 foreach,而不是直接操作枚举数。Therefore, using foreach is recommended, instead of directly manipulating the enumerator.

枚举器可用于读取集合中的数据,但不能用于修改基础集合。Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

最初,枚举数定位在集合中第一个元素的前面。Initially, the enumerator is positioned before the first element in the collection. Reset 也会将枚举器放回此位置。Reset also brings the enumerator back to this position. 在此位置上,未定义 CurrentAt this position, Current is undefined. 因此,在读取 MoveNext 的值之前,必须调用 Current 将枚举器向前移动到集合的第一个元素。Therefore, you must call MoveNext to advance the enumerator to the first element of the collection before reading the value of Current.

在调用 CurrentMoveNext 之前,Reset 返回同一对象。Current returns the same object until either MoveNext or Reset is called. MoveNextCurrent 设置为下一个元素。MoveNext sets Current to the next element.

如果 MoveNext 越过集合的末尾,则枚举器将定位在集合中最后一个元素之后,并 MoveNext 返回 falseIf MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. 当枚举器位于此位置时,对的后续调用 MoveNext 也将返回 falseWhen the enumerator is at this position, subsequent calls to MoveNext also return false. 如果最后一次调用 MoveNext 返回 falseCurrent 则未定义。If the last call to MoveNext returned false, Current is undefined. 若要再次将 Current 设置为集合的第一个元素,可以调用 Reset 并接着调用 MoveNextTo set Current to the first element of the collection again, you can call Reset followed by MoveNext.

只要集合保持不变,枚举器就仍有效。An enumerator remains valid as long as the collection remains unchanged. 如果对集合进行更改(如添加、修改或删除元素),则枚举数将失效且不可恢复,而且其行为是不确定的。If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior is undefined.

枚举数没有对集合的独占访问权;因此,从头到尾对一个集合进行枚举在本质上不是一个线程安全的过程。The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. 若要确保枚举过程中的线程安全性,可以在整个枚举过程中锁定集合。To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. 若要允许多个线程访问集合以进行读写操作,则必须实现自己的同步。To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

此方法是一种 O(1) 操作。This method is an O(1) operation.

另请参阅

适用于

产品 Introduced

GetEnumerator(Int32, Int32)

返回 ArrayList 中元素范围的枚举器。Returns an enumerator for a range of elements in the ArrayList.

public:
 virtual System::Collections::IEnumerator ^ GetEnumerator(int index, int count);
public virtual System.Collections.IEnumerator GetEnumerator (int index, int count);
abstract member GetEnumerator : int * int -> System.Collections.IEnumerator
override this.GetEnumerator : int * int -> System.Collections.IEnumerator
Public Overridable Function GetEnumerator (index As Integer, count As Integer) As IEnumerator

参数

index
Int32

枚举器应引用的 ArrayList 部分从零开始的起始索引。The zero-based starting index of the ArrayList section that the enumerator should refer to.

count
Int32

枚举器应引用的 ArrayList 部分中的元素数。The number of elements in the ArrayList section that the enumerator should refer to.

返回

IEnumerator

ArrayList 中指定的元素范围的 IEnumeratorAn IEnumerator for the specified range of elements in the ArrayList.

例外

index 小于零。index is less than zero.

- 或 --or- count 小于零。count is less than zero.

indexcount 未在 ArrayList 中指定有效范围。index and count do not specify a valid range in the ArrayList.

示例

下面的示例获取的枚举器 ArrayList ,以及中某个元素范围的枚举器 ArrayListThe following example gets the enumerator for an ArrayList, and the enumerator for a range of elements in the ArrayList.

using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        ArrayList colors = new ArrayList();
        colors.Add("red");
        colors.Add("blue");
        colors.Add("green");
        colors.Add("yellow");
        colors.Add("beige");
        colors.Add("brown");
        colors.Add("magenta");
        colors.Add("purple");

        IEnumerator e = colors.GetEnumerator();
        while (e.MoveNext())
        {
            Object obj = e.Current;
            Console.WriteLine(obj);
        }

        Console.WriteLine();

        IEnumerator e2 = colors.GetEnumerator(2, 4);
        while (e2.MoveNext())
        {
            Object obj = e2.Current;
            Console.WriteLine(obj);
        }
    }
}

/* This code example produces
   the following ouput:
    red
    blue
    green
    yellow
    beige
    brown
    magenta
    purple

    green
    yellow
    beige
    brown
 */
Imports System.Collections

Class Program
    Private Shared Sub Main(ByVal args As String())
        Dim colors As New ArrayList()
        colors.Add("red")
        colors.Add("blue")
        colors.Add("green")
        colors.Add("yellow")
        colors.Add("beige")
        colors.Add("brown")
        colors.Add("magenta")
        colors.Add("purple")
        
        Dim e As IEnumerator = colors.GetEnumerator()
        While e.MoveNext()
            Dim obj As [Object] = e.Current
            Console.WriteLine(obj)
        End While
        
        Console.WriteLine()
        
        Dim e2 As IEnumerator = colors.GetEnumerator(2, 4)
        While e2.MoveNext()
            Dim obj As [Object] = e2.Current
            Console.WriteLine(obj)
        End While
    End Sub
End Class

' This code example produces
' the following ouput:
' red
' blue
' green
' yellow
' beige
' brown
' magenta
' purple
'
' green
' yellow
' beige
' brown
' 

注解

foreachC # 语言的语句 for each 在 Visual C++ 中 (, For Each Visual Basic) 隐藏了枚举器的复杂性。The foreach statement of the C# language (for each in Visual C++, For Each Visual Basic) hides the complexity of the enumerators. 因此,建议使用 foreach,而不是直接操作枚举数。Therefore, using foreach is recommended, instead of directly manipulating the enumerator.

枚举器可用于读取集合中的数据,但不能用于修改基础集合。Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

最初,枚举数定位在集合中第一个元素的前面。Initially, the enumerator is positioned before the first element in the collection. Reset 也会将枚举器放回此位置。Reset also brings the enumerator back to this position. 在此位置上,未定义 CurrentAt this position, Current is undefined. 因此,在读取 MoveNext 的值之前,必须调用 Current 将枚举器向前移动到集合的第一个元素。Therefore, you must call MoveNext to advance the enumerator to the first element of the collection before reading the value of Current.

在调用 CurrentMoveNext 之前,Reset 返回同一对象。Current returns the same object until either MoveNext or Reset is called. MoveNextCurrent 设置为下一个元素。MoveNext sets Current to the next element.

如果 MoveNext 越过集合的末尾,则枚举器将定位在集合中最后一个元素之后,并 MoveNext 返回 falseIf MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. 当枚举器位于此位置时,对的后续调用 MoveNext 也将返回 falseWhen the enumerator is at this position, subsequent calls to MoveNext also return false. 如果最后一次调用 MoveNext 返回 falseCurrent 则未定义。If the last call to MoveNext returned false, Current is undefined. 若要再次将 Current 设置为集合的第一个元素,可以调用 Reset 并接着调用 MoveNextTo set Current to the first element of the collection again, you can call Reset followed by MoveNext.

只要集合保持不变,枚举器就仍有效。An enumerator remains valid as long as the collection remains unchanged. 如果对集合进行更改(如添加、修改或删除元素),则枚举数将失效且不可恢复,而且其行为是不确定的。If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior is undefined.

枚举数没有对集合的独占访问权;因此,从头到尾对一个集合进行枚举在本质上不是一个线程安全的过程。The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. 若要确保枚举过程中的线程安全性,可以在整个枚举过程中锁定集合。To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. 若要允许多个线程访问集合以进行读写操作,则必须实现自己的同步。To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

此方法是一种 O(1) 操作。This method is an O(1) operation.

版本兼容性Version Compatibility

在 .NET Framework 版本1.0 和1.1 中,方法返回的包装器的枚举器将 ArrayList Adapter 第二个参数视为上限而不是计数。In the .NET Framework versions 1.0 and 1.1, the enumerator for an ArrayList wrapper returned by the Adapter method treated the second argument as an upper bound rather than as a count. 在中, .NET Framework 2.0.NET Framework 2.0 第二个参数被正确地视为计数。In the .NET Framework 2.0.NET Framework 2.0 the second argument is correctly treated as a count.

另请参阅

适用于

产品 Introduced