Articolo
11/17/2011

IDictionaryEnumerator Interface

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Enumerates the elements of a nongeneric dictionary.

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

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public Interface IDictionaryEnumerator _
    Inherits IEnumerator

[ComVisibleAttribute(true)]
public interface IDictionaryEnumerator : IEnumerator

The IDictionaryEnumerator type exposes the following members.

Properties

	Name	Description
	Current	Gets the current element in the collection. (Inherited from IEnumerator.)
	Entry	Gets both the key and the value of the current dictionary entry.
	Key	Gets the key of the current dictionary entry.
	Value	Gets the value of the current dictionary entry.

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Methods

	Name	Description
	MoveNext	Advances the enumerator to the next element of the collection. (Inherited from IEnumerator.)
	Reset	Sets the enumerator to its initial position, which is before the first element in the collection. (Inherited from IEnumerator.)

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Remarks

[Visual Basic, C#]

The foreach statement of the C# language (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. The Reset method also brings the enumerator back to this position. At this position, calling the Current property throws an exception. 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 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, calling Current throws an exception. 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, modifying, or deleting elements, the enumerator is irrecoverably invalidated and the next call to MoveNext or Reset throws an InvalidOperationException. 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.

The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. 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.

Notes to Implementers

The Current property that is inherited from IEnumerator returns an Object that is a boxed DictionaryEntry, similar to the return value of the Entry property.

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.

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