Dictionary<TKey,TValue>.KeyCollection.Enumerator Struct


列舉 Dictionary<TKey,TValue>.KeyCollection 的項目。Enumerates the elements of a Dictionary<TKey,TValue>.KeyCollection.

public: value class Dictionary<TKey, TValue>::KeyCollection::Enumerator : System::Collections::Generic::IEnumerator<TKey>
public struct Dictionary<TKey,TValue>.KeyCollection.Enumerator : System.Collections.Generic.IEnumerator<TKey>
public struct Dictionary<TKey,TValue>.KeyCollection.Enumerator : System.Collections.Generic.IEnumerator<TKey>
type Dictionary<'Key, 'Value>.KeyCollection.Enumerator = struct
    interface IEnumerator<'Key>
    interface IEnumerator
    interface IDisposable
type Dictionary<'Key, 'Value>.KeyCollection.Enumerator = struct
    interface IEnumerator<'Key>
    interface IDisposable
    interface IEnumerator
Public Structure Dictionary(Of TKey, TValue).KeyCollection.Enumerator
Implements IEnumerator(Of TKey)

Type Parameters



C#語言的 foreach 語句(for each 中C++的 For Each,Visual Basic 中的)會隱藏枚舉器的複雜性。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. 在這個位置上,Current 並未定義。At this position, Current is undefined. 您必須先呼叫 MoveNext,將列舉值前移至集合的第一個元素,然後再讀取 Current的值。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 MoveNextCurrent returns the same object until MoveNext 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. 您不能再次將 Current 設定為集合的第一個項目;您必須建立新的列舉值執行個體。You cannot set Current to the first element of the collection again; you must create a new enumerator instance instead.

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,例如加入專案或變更容量,枚舉器會失效,而下一次呼叫 MoveNextIEnumerator.Reset 則會擲回 InvalidOperationExceptionIf changes are made to the collection, such as adding elements or changing the capacity, the enumerator is irrecoverably invalidated and the next call to MoveNext or IEnumerator.Reset throws an InvalidOperationException.

僅限 .NET Core 3.0 +:不使列舉值失效的唯一改變方法會 RemoveClear.NET Core 3.0+ only: The only mutating methods which do not invalidate enumerators are Remove and Clear.

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 中集合的預設實值不會同步處理。Default implementations of collections in System.Collections.Generic are not synchronized.



取得位於目前列舉值位置的項目。Gets the element at the current position of the enumerator.



釋放 Dictionary<TKey,TValue>.KeyCollection.Enumerator 使用的所有資源。Releases all resources used by the Dictionary<TKey,TValue>.KeyCollection.Enumerator.


將列舉值前移至 Dictionary<TKey,TValue>.KeyCollection 的下一個項目。Advances the enumerator to the next element of the Dictionary<TKey,TValue>.KeyCollection.

Explicit Interface Implementations


取得位於目前列舉值位置的項目。Gets the element at the current position of the enumerator.


將列舉值設定為其初始位置,在集合的第一個元素之前。Sets the enumerator to its initial position, which is before the first element in the collection.

Applies to

See also