Dictionary<TKey, TValue> Constructor ()
Initializes a new instance of the Dictionary<TKey, TValue> class that is empty, has the default initial capacity, and uses the default equality comparer for the key type.
Assembly: mscorlib (in mscorlib.dll)
Every key in a Dictionary<TKey, TValue> must be unique according to the default equality comparer.
Dictionary<TKey, TValue> requires an equality implementation to determine whether keys are equal. This constructor uses the default generic equality comparer, EqualityComparer<T>.Default. If type TKey implements the System.IEquatable<T> generic interface, the default equality comparer uses that implementation. Alternatively, you can specify an implementation of the IEqualityComparer<T> generic interface by using a constructor that accepts a comparer parameter.
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If you can estimate the size of the collection, using a constructor that specifies the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Dictionary<TKey, TValue>. |
This constructor is an O(1) operation.
The following code example creates an empty Dictionary<TKey, TValue> of strings with string keys and uses the Add method to add some elements. The example demonstrates that the Add method throws an ArgumentException when attempting to add a duplicate key.
This code example is part of a larger example provided for the Dictionary<TKey, TValue> class.
// Create a new dictionary of strings, with string keys. // Dictionary<string, string> openWith = new Dictionary<string, string>(); // Add some elements to the dictionary. There are no // duplicate keys, but some of the values are duplicates. openWith.Add("txt", "notepad.exe"); openWith.Add("bmp", "paint.exe"); openWith.Add("dib", "paint.exe"); openWith.Add("rtf", "wordpad.exe"); // The Add method throws an exception if the new key is // already in the dictionary. try { openWith.Add("txt", "winword.exe"); } catch (ArgumentException) { Console.WriteLine("An element with Key = \"txt\" already exists."); }
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
