Dictionary(TKey, TValue).Item Property
Gets or sets the value associated with the specified key.
Assemblies: mscorlib (in mscorlib.dll)
System.Collections (in System.Collections.dll)
abstract Item : key:'TKey -> 'TValue with get, set override Item : key:'TKey -> 'TValue with get, set
- Type: TKey
The key of the value to get or set.
Property ValueType: TValue
The value associated with the specified key. If the specified key is not found, a get operation throws a KeyNotFoundException, and a set operation creates a new element with the specified key.
This property provides the ability to access a specific element in the collection by using the following C# syntax: myCollection[key] (myCollection(key) in Visual Basic).
You can also use the property to add new elements by setting the value of a key that does not exist in the Dictionary(TKey, TValue). When you set the property value, if the key is in the Dictionary(TKey, TValue), the value associated with that key is replaced by the assigned value. If the key is not in the Dictionary(TKey, TValue), the key and value are added to the dictionary. In contrast, the Add method does not modify existing elements.
A key cannot be a null reference (Nothing in Visual Basic), but a value can be, if the value type TValue is a reference type.
The C# language uses the this keyword to define the indexers instead of implementing the property. Visual Basic implements as a default property, which provides the same indexing functionality.
Getting or setting the value of this property approaches an O(1) operation.
The following code example uses the property (the indexer in C#) to retrieve values, demonstrating that a KeyNotFoundException is thrown when a requested key is not present, and showing that the value associated with a key can be replaced.
The example also shows how to use the TryGetValue method as a more efficient way to retrieve values if a program often must try key values that are not in the dictionary.
This code example is part of a larger example provided for the Dictionary(TKey, TValue) class. openWith is the name of the Dictionary used in this example.
.NET FrameworkSupported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0
.NET Framework Client ProfileSupported in: 4, 3.5 SP1
Portable Class LibrarySupported in: Portable Class Library
.NET for Windows Store appsSupported in: Windows 8
Supported in: Windows Phone 8.1
Supported in: Windows Phone Silverlight 8.1
Supported in: Windows Phone Silverlight 8
Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.