Dictionary<TKey,TValue>.KeyCollection.IEnumerable.GetEnumerator Method
Definition
Important
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Returns an enumerator that iterates through a collection.
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.IEnumeratorFunction GetEnumerator () As IEnumerator Implements IEnumerable.GetEnumeratorReturns
An IEnumerator that can be used to iterate through the collection.
Implements
Remarks
The foreach statement of the C# language (for each in C++, For Each in Visual Basic) hides the complexity of the enumerators. Therefore, using foreach is recommended, instead of directly manipulating the enumerator.
Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.
Initially, the enumerator is positioned before the first element in the collection. Reset also brings the enumerator back to this position. At this position, Current is undefined. Therefore, you must call MoveNext to advance the enumerator to the first element of the collection before reading the value of Current.
Current returns the same object until either MoveNext or Reset is called. MoveNext sets Current to the next element.
If MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. When the enumerator is at this position, subsequent calls to MoveNext also return false. If the last call to MoveNext returned false, Current is undefined. To set Current to the first element of the collection again, you can call Reset followed by MoveNext.
An enumerator remains valid as long as the collection remains unchanged. If 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.
.NET Core 3.0+ only: The only mutating methods which do not invalidate enumerators are Remove and Clear.
The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.
Default implementations of collections in System.Collections.Generic are not synchronized.
This method is an O(1) operation.
