Dictionary<TKey, TValue>.IDictionary.Keys Property

Gets an ICollection containing the keys of the IDictionary.

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

ICollection IDictionary.Keys { get; }

Property Value

Type: System.Collections.ICollection
An ICollection containing the keys of the IDictionary.



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.

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.

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";




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

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

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