Dictionary<TKey, TValue>.IDictionary.Keys Property
Microsoft Silverlight will reach end of support after October 2021. Learn more.
Gets an ICollection containing the keys of the IDictionary.
Namespace: System.Collections.Generic
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Private ReadOnly Property Keys As ICollection
Implements IDictionary.Keys
ICollection IDictionary.Keys { get; }
Property Value
Type: System.Collections.ICollection
An ICollection containing the keys of the IDictionary.
Implements
Remarks
The order of the keys in the returned ICollection is unspecified, but it is guaranteed to be the same order as the corresponding values in the ICollection returned by the Values property.
Getting the value of this property is an O(1) operation.
Examples
The following code example shows how to use the IDictionary.Keys property of the System.Collections.IDictionary interface with a Dictionary<TKey, TValue>, to list the keys in the dictionary. The example also shows how to enumerate the key/value pairs in the dictionary; 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.
Imports System.Collections
Imports System.Collections.Generic
Public Class Example
Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
' 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")
...
' To get the keys alone, use the Keys property.
icoll = openWith.Keys
' The elements of the collection are strongly typed
' with the type that was specified for dictionary keys,
' even though the ICollection interface is not strongly
' typed.
outputBlock.Text &= vbCrLf
For Each s As String In icoll
outputBlock.Text &= String.Format("Key = {0}", s) & vbCrLf
Next s
...
' When you use foreach to enumerate dictionary elements
' with the IDictionary interface, the elements are retrieved
' as DictionaryEntry objects instead of KeyValuePair objects.
outputBlock.Text &= vbCrLf
For Each de As DictionaryEntry In openWith
outputBlock.Text &= String.Format("Key = {0}, Value = {1}", _
de.Key, de.Value) & vbCrLf
Next
...
End Sub
End Class
using System;
using System.Collections;
using System.Collections.Generic;
public class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
// 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");
...
// To get the keys alone, use the Keys property.
icoll = openWith.Keys;
// The elements of the collection are strongly typed
// with the type that was specified for dictionary keys,
// even though the ICollection interface is not strongly
// typed.
outputBlock.Text += "\n";
foreach (string s in icoll)
{
outputBlock.Text += String.Format("Key = {0}", s) + "\n";
}
...
// When you use foreach to enumerate dictionary elements
// with the IDictionary interface, the elements are retrieved
// as DictionaryEntry objects instead of KeyValuePair objects.
outputBlock.Text += "\n";
foreach (DictionaryEntry de in openWith)
{
outputBlock.Text += String.Format("Key = {0}, Value = {1}",
de.Key, de.Value) + "\n";
}
...
}
}
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.