Dictionary<TKey,TValue>.IDictionary.GetEnumerator Method
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Returns an IDictionaryEnumerator for the IDictionary.
virtual System::Collections::IDictionaryEnumerator ^ System.Collections.IDictionary.GetEnumerator() = System::Collections::IDictionary::GetEnumerator;System.Collections.IDictionaryEnumerator IDictionary.GetEnumerator ();abstract member System.Collections.IDictionary.GetEnumerator : unit -> System.Collections.IDictionaryEnumerator
override this.System.Collections.IDictionary.GetEnumerator : unit -> System.Collections.IDictionaryEnumeratorFunction GetEnumerator () As IDictionaryEnumerator Implements IDictionary.GetEnumeratorReturns
An IDictionaryEnumerator for the IDictionary.
Implements
Examples
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");
open System
open System.Collections
open System.Collections.Generic
// Create a new dictionary of strings, with string keys,
// and access it using the IDictionary interface.
let openWith: IDictionary = 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")
Imports System.Collections
Imports System.Collections.Generic
Public Class Example
Public Shared Sub Main()
' Create a new dictionary of strings, with string keys,
' and access it using the IDictionary interface.
'
Dim openWith As IDictionary = _
New Dictionary(Of 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.
Console.WriteLine();
foreach( DictionaryEntry de in openWith )
{
Console.WriteLine("Key = {0}, Value = {1}",
de.Key, de.Value);
}
// When you use foreach to enumerate dictionary elements
// with the IDictionary interface, the elements are retrieved
// as DictionaryEntry objects instead of KeyValuePair objects.
printfn ""
for de in openWith do
let de = de :?> DictionaryEntry
printfn $"For key = {de.Key}, value = {de.Value}"
' When you use foreach to enumerate dictionary elements
' with the IDictionary interface, the elements are retrieved
' as DictionaryEntry objects instead of KeyValuePair objects.
Console.WriteLine()
For Each de As DictionaryEntry In openWith
Console.WriteLine("Key = {0}, Value = {1}", _
de.Key, de.Value)
Next
}
}
End Sub
End Class
Remarks
For purposes of enumeration, each item is a DictionaryEntry structure.
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, Entry 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 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 the System.Collections.Generic namespace are not synchronized.
This method is an O(1) operation.
