DictionaryBase.IEnumerable.GetEnumerator 方法

定義

傳回透過 IEnumerator 重複的 DictionaryBaseReturns an IEnumerator that iterates through the DictionaryBase.

 virtual System::Collections::IEnumerator ^ System.Collections.IEnumerable.GetEnumerator() = System::Collections::IEnumerable::GetEnumerator;
System.Collections.IEnumerator IEnumerable.GetEnumerator ();
abstract member System.Collections.IEnumerable.GetEnumerator : unit -> System.Collections.IEnumerator
override this.System.Collections.IEnumerable.GetEnumerator : unit -> System.Collections.IEnumerator
Function GetEnumerator () As IEnumerator Implements IEnumerable.GetEnumerator

傳回

IEnumerator

IEnumeratorDictionaryBaseAn IEnumerator for the DictionaryBase.

實作

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,呼叫會擲回 Current 例外狀況。At this position, calling Current throws an exception. 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,然後 MoveNext 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. 當列舉值位於這個位置時,後續呼叫 MoveNext 也會傳回 falseWhen the enumerator is at this position, subsequent calls to MoveNext also return false. 如果最後一次呼叫 MoveNext 傳回,則呼叫會擲回 false 例外狀況 CurrentIf the last call to MoveNext returned false, calling Current throws an exception. 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. 如果對集合進行了變更,例如加入、修改或刪除元素,列舉值將無法回復地失效,且下一次呼叫或會擲回 MoveNext Reset InvalidOperationExceptionIf 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. 如果在和之間修改集合,則會傳回 MoveNext Current 它所 Current 設定的元素,即使列舉值已經無效。If the collection is modified between MoveNext and Current, Current returns the element that it is set to, even if the enumerator is already invalidated.

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. 即使集合經過同步化,其他的執行緒仍可修改該集合,使列舉值擲回例外狀況。Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. 若要保證列舉過程的執行緒安全,您可以在整個列舉過程中鎖定集合,或攔截由其他執行緒的變更所造成的例外狀況。To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

這個方法是一項作業 O(1)This method is an O(1) operation.

適用於

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