ArrayList.GetEnumerator 方法

定義

傳回逐一查看 ArrayList 的列舉值。Returns an enumerator that iterates through the ArrayList.

多載

GetEnumerator()

傳回整個 ArrayList 的列舉值。Returns an enumerator for the entire ArrayList.

GetEnumerator(Int32, Int32)

傳回適用於 ArrayList 中某段範圍項目的列舉程式。Returns an enumerator for a range of elements in the ArrayList.

GetEnumerator()

傳回整個 ArrayList 的列舉值。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

傳回

整個 IEnumeratorArrayListAn IEnumerator for the entire ArrayList.

實作

範例

下列範例會取得 ArrayList的列舉值,以及 ArrayList中某範圍專案的枚舉器。The 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
' 

備註

C# 語言的 foreach 陳述式 (在 Visual Basic 中為 for each) 會隱藏列舉值的複雜度。The foreach statement of the C# language (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. Reset 也會將列舉值帶回至這個位置。Reset also brings the enumerator back to this position. 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 MoveNextResetCurrent returns the same object until either MoveNext or Reset 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. 若要再次將 Current 設定為集合的第一個元素,您可以在呼叫 Reset 之後,接著呼叫 MoveNextTo set Current to the first element of the collection again, you can call Reset followed by MoveNext.

只要集合維持不變,列舉值就仍維持有效。An enumerator remains valid as long as the collection remains unchanged. 如果對集合進行變更,例如加入、修改或刪除項目,列舉程式會永久失效,且其行為未定義。If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior 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.

這個方法是 O(1) 作業。This method is an O(1) operation.

另請參閱

GetEnumerator(Int32, Int32)

傳回適用於 ArrayList 中某段範圍項目的列舉程式。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

參數

index
Int32

列舉程式應參考之 ArrayList 區段以零為起始的起始索引。The zero-based starting index of the ArrayList section that the enumerator should refer to.

count
Int32

列舉程式應參考之 ArrayList 區段中的項目數。The number of elements in the ArrayList section that the enumerator should refer to.

傳回

適用於 IEnumerator 中某指定項目範圍的 ArrayListAn IEnumerator for the specified range of elements in the ArrayList.

例外狀況

index 小於零。index is less than zero.

-或--or- count 小於零。count is less than zero.

indexcount 未指定 ArrayList 中的有效範圍。index and count do not specify a valid range in the ArrayList.

範例

下列範例會取得 ArrayList的列舉值,以及 ArrayList中某範圍專案的枚舉器。The 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
' 

備註

C#語言的 foreach 語句(在視覺效果C++中為for each For Each Visual Basic)會隱藏列舉值的複雜度。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. Reset 也會將列舉值帶回至這個位置。Reset also brings the enumerator back to this position. 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 MoveNextResetCurrent returns the same object until either MoveNext or Reset 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. 若要再次將 Current 設定為集合的第一個元素,您可以在呼叫 Reset 之後,接著呼叫 MoveNextTo set Current to the first element of the collection again, you can call Reset followed by MoveNext.

只要集合維持不變,列舉值就仍維持有效。An enumerator remains valid as long as the collection remains unchanged. 如果對集合進行變更,例如加入、修改或刪除項目,列舉程式會永久失效,且其行為未定義。If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior 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.

這個方法是 O(1) 作業。This method is an O(1) operation.

版本相容性Version Compatibility

在 .NET Framework 版本1.0 和1.1 中,Adapter 方法所傳回之 ArrayList 包裝函式的列舉值,會將第二個引數視為上限,而不是計數。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. .NET Framework 2.0.NET Framework 2.0 會將第二個引數正確地視為計數。In the .NET Framework 2.0.NET Framework 2.0 the second argument is correctly treated as a count.

另請參閱

適用於