Hashtable.GetEnumerator 方法

定義

傳回透過 IDictionaryEnumerator 重複的 HashtableReturns an IDictionaryEnumerator that iterates through the Hashtable.

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

傳回

實作

範例

下列範例會比較 GetEnumeratorforeach 的用法,以列舉 Hashtable的內容。The following example compares the use of GetEnumerator and foreach to enumerate the contents of a Hashtable.

using namespace System;
using namespace System::Collections;

public class HashtableExample
{
public:
    static void Main()
    {
        // Creates and initializes a new Hashtable.
        Hashtable^ clouds = gcnew Hashtable();
        clouds->Add("Cirrus", "Castellanus");
        clouds->Add("Cirrocumulus", "Stratiformis");
        clouds->Add("Altostratus", "Radiatus");
        clouds->Add("Stratocumulus", "Perlucidus");
        clouds->Add("Stratus", "Fractus");
        clouds->Add("Nimbostratus", "Pannus");
        clouds->Add("Cumulus", "Humilis");
        clouds->Add("Cumulonimbus", "Incus");

        // Displays the keys and values of the Hashtable using GetEnumerator()

        IDictionaryEnumerator^ denum = clouds->GetEnumerator();
        DictionaryEntry dentry;

        Console::WriteLine();
        Console::WriteLine("    Cloud Type       Variation");
        Console::WriteLine("    -----------------------------");
        while (denum->MoveNext())
        {
            dentry = (DictionaryEntry) denum->Current;
            Console::WriteLine("    {0,-17}{1}", dentry.Key, dentry.Value);
        }
        Console::WriteLine();

        // Displays the keys and values of the Hashtable using foreach statement

        Console::WriteLine("    Cloud Type       Variation");
        Console::WriteLine("    -----------------------------");
        for each (DictionaryEntry de in clouds)
        {
            Console::WriteLine("    {0,-17}{1}", de.Key, de.Value);
        }
        Console::WriteLine();
    }
};

int main()
{
    HashtableExample::Main();
}

// The program displays the following output to the console:
//
//    Cloud Type       Variation
//    -----------------------------
//    Cirrocumulus     Stratiformis
//    Stratocumulus    Perlucidus
//    Cirrus           Castellanus
//    Cumulus          Humilis
//    Nimbostratus     Pannus
//    Stratus          Fractus
//    Altostratus      Radiatus
//    Cumulonimbus     Incus
//
//    Cloud Type       Variation
//    -----------------------------
//    Cirrocumulus     Stratiformis
//    Stratocumulus    Perlucidus
//    Cirrus           Castellanus
//    Cumulus          Humilis
//    Nimbostratus     Pannus
//    Stratus          Fractus
//    Altostratus      Radiatus
//    Cumulonimbus     Incus*/
using System;
using System.Collections;

public class HashtableExample
{
    public static void Main()
    {
        // Creates and initializes a new Hashtable.
        Hashtable clouds = new Hashtable();
        clouds.Add("Cirrus", "Castellanus");
        clouds.Add("Cirrocumulus", "Stratiformis");
        clouds.Add("Altostratus", "Radiatus");
        clouds.Add("Stratocumulus", "Perlucidus");
        clouds.Add("Stratus", "Fractus");
        clouds.Add("Nimbostratus", "Pannus");
        clouds.Add("Cumulus", "Humilis");
        clouds.Add("Cumulonimbus", "Incus");

        // Displays the keys and values of the Hashtable using GetEnumerator()

        IDictionaryEnumerator denum = clouds.GetEnumerator();
        DictionaryEntry dentry;

        Console.WriteLine();
        Console.WriteLine("    Cloud Type       Variation");
        Console.WriteLine("    -----------------------------");
        while (denum.MoveNext())
        {
            dentry = (DictionaryEntry) denum.Current;
            Console.WriteLine("    {0,-17}{1}", dentry.Key, dentry.Value);
        }
        Console.WriteLine();

        // Displays the keys and values of the Hashtable using foreach statement

        Console.WriteLine("    Cloud Type       Variation");
        Console.WriteLine("    -----------------------------");
        foreach (DictionaryEntry de in clouds)
        {
            Console.WriteLine("    {0,-17}{1}", de.Key, de.Value);
        }
        Console.WriteLine();
    }
}

// The program displays the following output to the console:
//
//    Cloud Type       Variation
//    -----------------------------
//    Cirrocumulus     Stratiformis
//    Stratocumulus    Perlucidus
//    Cirrus           Castellanus
//    Cumulus          Humilis
//    Nimbostratus     Pannus
//    Stratus          Fractus
//    Altostratus      Radiatus
//    Cumulonimbus     Incus
//
//    Cloud Type       Variation
//    -----------------------------
//    Cirrocumulus     Stratiformis
//    Stratocumulus    Perlucidus
//    Cirrus           Castellanus
//    Cumulus          Humilis
//    Nimbostratus     Pannus
//    Stratus          Fractus
//    Altostratus      Radiatus
//    Cumulonimbus     Incus*/
Imports System.Collections

Public Class HashtableExample
    Public Shared Sub Main()
        ' Creates and initializes a new Hashtable.
        Dim clouds As New Hashtable()
        clouds.Add("Cirrus", "Castellanus")
        clouds.Add("Cirrocumulus", "Stratiformis")
        clouds.Add("Altostratus", "Radiatus")
        clouds.Add("Stratocumulus", "Perlucidus")
        clouds.Add("Stratus", "Fractus")
        clouds.Add("Nimbostratus", "Pannus")
        clouds.Add("Cumulus", "Humilis")
        clouds.Add("Cumulonimbus", "Incus")

        ' Displays the keys and values of the Hashtable using GetEnumerator()

        Dim denum As IDictionaryEnumerator = clouds.GetEnumerator()
        Dim dentry As DictionaryEntry

        Console.WriteLine()
        Console.WriteLine("    Cloud Type       Variation")
        Console.WriteLine("    -----------------------------")
        While denum.MoveNext()
            dentry = CType(denum.Current, DictionaryEntry)
            Console.WriteLine("    {0,-17}{1}", dentry.Key, dentry.Value)
        End While
        Console.WriteLine()

        ' Displays the keys and values of the Hashtable using foreach statement

        Console.WriteLine("    Cloud Type       Variation")
        Console.WriteLine("    -----------------------------")
        For Each de As DictionaryEntry in clouds
            Console.WriteLine("    {0,-17}{1}", de.Key, de.Value)
        Next de
        Console.WriteLine()
    End Sub
End Class

' The program displays the following output to the console:
'
'    Cloud Type       Variation
'    -----------------------------
'    Cirrocumulus     Stratiformis
'    Stratocumulus    Perlucidus
'    Cirrus           Castellanus
'    Cumulus          Humilis
'    Nimbostratus     Pannus
'    Stratus          Fractus
'    Altostratus      Radiatus
'    Cumulonimbus     Incus
'
'    Cloud Type       Variation
'    -----------------------------
'    Cirrocumulus     Stratiformis
'    Stratocumulus    Perlucidus
'    Cirrus           Castellanus
'    Cumulus          Humilis
'    Nimbostratus     Pannus
'    Stratus          Fractus
'    Altostratus      Radiatus
'    Cumulonimbus     Incus*/

備註

[Visual Basic, C#][Visual Basic, C#]

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.

列舉值對集合並沒有獨佔存取,因此列舉集合在本質上並非安全執行緒的程序。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.

因為序列化和還原序列化 Hashtable 的列舉值可能會導致元素重新排序,所以不能在不呼叫 Reset 方法的情況下繼續列舉。Because serializing and deserializing an enumerator for a Hashtable can cause the elements to become reordered, it is not possible to continue enumeration without calling the Reset method.

適用於

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