Статья
11/18/2011

Dictionary<TKey, TValue>.KeyCollection.Enumerator Structure

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Enumerates the elements of a Dictionary<TKey, TValue>.KeyCollection.

Namespace: System.Collections.Generic
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Structure Enumerator _
    Implements IEnumerator(Of TKey), IDisposable, IEnumerator

public struct Enumerator : IEnumerator<TKey>, 
    IDisposable, IEnumerator

The Dictionary<TKey, TValue>.KeyCollection.Enumerator type exposes the following members.

Properties

	Name	Description
	Current	Gets the element at the current position of the enumerator.

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Methods

	Name	Description
	Dispose	Releases all resources used by the Dictionary<TKey, TValue>.KeyCollection.Enumerator.
	Equals	Indicates whether this instance and a specified object are equal. (Inherited from ValueType.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Returns the hash code for this instance. (Inherited from ValueType.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	MoveNext	Advances the enumerator to the next element of the Dictionary<TKey, TValue>.KeyCollection.
	ToString	Returns the fully qualified type name of this instance. (Inherited from ValueType.)

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Explicit Interface Implementations

	Name	Description
	IEnumerator.Current	Gets the element at the current position of the enumerator.
	IEnumerator.Reset	Sets the enumerator to its initial position, which is before the first element in the collection.

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Remarks

The foreach statement of the C# language (for each in C++, For Each in Visual Basic) hides the complexity of 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. 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 MoveNext 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. You cannot set Current to the first element of the collection again; you must create a new enumerator instance instead.

An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and its behavior is undefined.

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.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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