Dictionary<TKey, TValue>::IDictionary::Item Property

private:
virtual property Object^ Item[Object^ key] {
	Object^ get (Object^ key) sealed = IDictionary::Item::get;
	void set (Object^ key, Object^ value) sealed = IDictionary::Item::set;
}

Implements

This property provides the ability to access a specific value in the collection by using the following C# syntax: myCollection[key] (myCollection(key) in Visual Basic).

You can also use the Item property to add new elements by setting the value of a key that does not exist in the dictionary; for example, myCollection["myNonexistentKey"] = myValue. However, if the specified key already exists in the dictionary, setting the Item property overwrites the old value. In contrast, the Add method does not modify existing elements.

The C# language uses the this keyword to define the indexers instead of implementing the IDictionary::Item property. Visual Basic implements IDictionary::Item 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 shows how to use the IDictionary::Item property (the indexer in C#) of the System.Collections::IDictionary interface with a Dictionary<TKey, TValue>, and ways the property differs from the Dictionary<TKey, TValue>::Item property.

The example shows that, like the Dictionary<TKey, TValue>::Item property, the Dictionary<TKey, TValue>::IDictionary::Item property can change the value associated with an existing key and can be used to add a new key/value pair if the specified key is not in the dictionary. The example also shows that unlike the Dictionary<TKey, TValue>::Item property, the Dictionary<TKey, TValue>::IDictionary::Item property does not throw an exception if key is not in the dictionary, returning a null reference instead. Finally, the example demonstrates that getting the Dictionary<TKey, TValue>::IDictionary::Item property returns a null reference if key is not the correct data type, and that setting the property throws an exception if key is not the correct data type.

The code example is part of a larger example, including output, provided for the IDictionary::Add method.

.NET Framework

.NET Framework Client Profile

Portable Class Library

.NET for Windows Store apps

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.

Reference