Dictionary<TKey, TValue>.Keys Property

Gets a collection containing the keys in the Dictionary<TKey, TValue>.

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

public Dictionary<T>.KeyCollection Keys { get; }

The order of the keys in the Dictionary<TKey, TValue>.KeyCollection is unspecified, but it is the same order as the associated values in the Dictionary<TKey, TValue>.ValueCollection returned by the Values property.

The returned Dictionary<TKey, TValue>.KeyCollection is not a static copy; instead, the Dictionary<TKey, TValue>.KeyCollection refers back to the keys in the original Dictionary<TKey, TValue>. Therefore, changes to the Dictionary<TKey, TValue> continue to be reflected in the Dictionary<TKey, TValue>.KeyCollection.

Getting the value of this property is an O(1) operation.

The following code example shows how to enumerate the keys in the dictionary using the Keys property, and how to enumerate the keys and values in the dictionary.

This code is part of a larger example that can be compiled and executed (openWith is the name of the Dictionary used in this example). See Dictionary<TKey, TValue>.

// To get the keys alone, use the Keys property.
Dictionary<string, string>.KeyCollection keyColl =
    openWith.Keys;

// The elements of the KeyCollection are strongly typed 
// with the type that was specified for dictionary keys.
Console.WriteLine();
foreach( string s in keyColl )
{
    Console.WriteLine("Key = {0}", s);
}


...


// When you use foreach to enumerate dictionary elements, 
// the elements are retrieved as KeyValuePair objects.
Console.WriteLine();
foreach( KeyValuePair<string, string> kvp in openWith )
{
    Console.WriteLine("Key = {0}, Value = {1}", 
        kvp.Key, kvp.Value);
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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