Dictionary<TKey,TValue>.IDictionary.GetEnumerator Dictionary<TKey,TValue>.IDictionary.GetEnumerator Dictionary<TKey,TValue>.IDictionary.GetEnumerator Method

定義

 virtual System::Collections::IDictionaryEnumerator ^ System.Collections.IDictionary.GetEnumerator() = System::Collections::IDictionary::GetEnumerator;
System.Collections.IDictionaryEnumerator IDictionary.GetEnumerator ();
Function GetEnumerator () As IDictionaryEnumerator Implements IDictionary.GetEnumerator

傳回

實作

範例

下列程式碼範例foreach示範如何使用語句(For Eachfor each中C++為 Visual Basic 中)來列舉字典中的索引鍵/值組,這會隱藏列舉值的使用。The following code example shows how to enumerate the key/value pairs in the dictionary by using the foreach statement (For Each in Visual Basic, for each in C++), which hides the use of the enumerator. 特別要注意的是, System.Collections.IDictionary DictionaryEntry介面的列舉值會傳回物件, KeyValuePair<TKey,TValue>而不是物件。In particular, note that the enumerator for the System.Collections.IDictionary interface returns DictionaryEntry objects rather than KeyValuePair<TKey,TValue> objects.

此程式碼範例是較大範例的一部分,包括針對IDictionary.Add方法提供的輸出。The code example is part of a larger example, including output, provided for the IDictionary.Add method.

using System;
using System.Collections;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        // Create a new dictionary of strings, with string keys,
        // and access it using the IDictionary interface.
        //
        IDictionary openWith = new Dictionary<string, string>();

        // Add some elements to the dictionary. There are no 
        // duplicate keys, but some of the values are duplicates.
        // IDictionary.Add throws an exception if incorrect types
        // are supplied for key or value.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("dib", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");
Imports System.Collections
Imports System.Collections.Generic

Public Class Example
    
    Public Shared Sub Main() 

        ' Create a new dictionary of strings, with string keys,
        ' and access it using the IDictionary interface.
        '
        Dim openWith As IDictionary = _
            New Dictionary(Of String, String)
        
        ' Add some elements to the dictionary. There are no 
        ' duplicate keys, but some of the values are duplicates.
        ' IDictionary.Add throws an exception if incorrect types
        ' are supplied for key or value.
        openWith.Add("txt", "notepad.exe")
        openWith.Add("bmp", "paint.exe")
        openWith.Add("dib", "paint.exe")
        openWith.Add("rtf", "wordpad.exe")
// When you use foreach to enumerate dictionary elements
// with the IDictionary interface, the elements are retrieved
// as DictionaryEntry objects instead of KeyValuePair objects.
Console.WriteLine();
foreach( DictionaryEntry de in openWith )
{
    Console.WriteLine("Key = {0}, Value = {1}", 
        de.Key, de.Value);
}
' When you use foreach to enumerate dictionary elements
' with the IDictionary interface, the elements are retrieved
' as DictionaryEntry objects instead of KeyValuePair objects.
Console.WriteLine()
For Each de As DictionaryEntry In openWith
    Console.WriteLine("Key = {0}, Value = {1}", _
        de.Key, de.Value)
Next 
    }
}

    End Sub

End Class

備註

基於列舉的目的,每個專案都DictionaryEntry是一個結構。For purposes of enumeration, each item is a DictionaryEntry structure.

foreach for each語言的語句(在 Visual Basic 中C++ )會隱藏枚舉器的複雜度。For Each C#The foreach statement of the C# language (for each in C++, For Each in Visual Basic) hides the complexity of 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方法也會將列舉值帶回此位置。The Reset method also brings the enumerator back to this position. 在這個位置上,Entry 並未定義。At this position, Entry is undefined. 因此,在讀取的MoveNext Entry值之前,您必須先呼叫方法,將枚舉器前移至集合的第一個元素。Therefore, you must call the MoveNext method to advance the enumerator to the first element of the collection before reading the value of Entry.

屬性會傳回相同的元素,直到呼叫MoveNextReset方法為止。 EntryThe Entry property returns the same element until either the MoveNext or Reset method is called. MoveNext 會將 Entry 設定為下一個項目。MoveNext sets Entry to the next element.

如果MoveNext傳遞集合的結尾,則列舉值會放置在集合中的最後一個元素之後falseMoveNext並傳回。If 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,後續的呼叫MoveNext false也會傳回。When the enumerator is at this position, subsequent calls to MoveNext also return false. 如果最後一次呼叫MoveNext傳回falseEntry則為未定義。If the last call to MoveNext returned false, Entry is undefined. 若要再次將 Entry 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 Entry to the first element of the collection again, you can call Reset followed by MoveNext.

只要集合維持不變,列舉程式就持續有效。An enumerator remains valid as long as the collection remains unchanged. 如果對集合進行了變更,例如加入、修改或刪除專案,枚舉器會失效,且下一次呼叫MoveNextReset InvalidOperationException會擲回。If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and the next call to MoveNext or Reset throws an InvalidOperationException.

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.

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

適用於

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