Collection.IEnumerable.GetEnumerator 方法


取得可逐一查看集合的列舉值。Gets an enumerator that iterates through the collection.

 virtual System::Collections::IEnumerator ^ ICollectionGetEnumerator() = System::Collections::IEnumerable::GetEnumerator;
System.Collections.IEnumerator IEnumerable.GetEnumerator ();
Function ICollectionGetEnumerator () As IEnumerator Implements IEnumerable.GetEnumerator


IEnumerator 物件,可用於逐一查看集合。An IEnumerator object that can be used to iterate through the collection.


[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 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,Current 屬性是未定義的。At this position, the Current property is undefined. 因此,您必須先呼叫 MoveNext 方法,將列舉值前移至集合的第一個元素,然後再讀取 Current的值。Therefore, you must call the MoveNext method 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 的最後一次呼叫會傳回 falseCurrent 未定義。If the last call to MoveNext returns 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.