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Dictionary<TKey, TValue>.IDictionary.GetEnumerator Method

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

IDictionaryEnumerator IDictionary.GetEnumerator()



For purposes of enumeration, each item is a KeyValuePair<TKey, TValue> structure representing a value and its key.

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. The Reset method also brings the enumerator back to this position. At this position, the Entry property is undefined. Therefore, you must call the MoveNext method to advance the enumerator to the first element of the collection before reading the value of Entry.

The Entry property returns the same element until either the MoveNext or Reset method is called. MoveNext sets Entry 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, Entry is undefined. To set Entry 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 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 the System.Collections.Generic namespace are not synchronized.

This method is an O(1) operation.

The following code example shows how to enumerate the key/value pairs in the dictionary by using the foreach statement (For Each in Visual Basic, for each in C++), which hides the use of the enumerator. In particular, note that the enumerator for the System.Collections.IDictionary interface returns DictionaryEntry objects rather than KeyValuePair<TKey, TValue> objects.

The code example is part of a larger example, including output, provided for the IDictionary.Add method.

using System;
using System.Collections;
using System.Collections.Generic;

public class Example
    public static void Main()
        // Create a new dictionary of strings, with string keys,
        // and access it using the IDictionary interface.
        IDictionary openWith = new Dictionary<string, string>();

        // Add some elements to the dictionary. There are no 
        // duplicate keys, but some of the values are duplicates.
        // IDictionary.Add throws an exception if incorrect types
        // are supplied for key or value.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("dib", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");


// When you use foreach to enumerate dictionary elements
// with the IDictionary interface, the elements are retrieved
// as DictionaryEntry objects instead of KeyValuePair objects.
foreach( DictionaryEntry de in openWith )
    Console.WriteLine("Key = {0}, Value = {1}", 
        de.Key, de.Value);



.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.