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IDictionary.Item Property

Gets or sets the element with the specified key.

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

Property Item ( _
	key As Object _
) As Object


Type: System.Object

The key of the element to get or set.

Property Value

Type: System.Object
The element with the specified key, or Nothing if the key does not exist.


key is Nothing.


The property is set and the IDictionary object is read-only.


The property is set, key does not exist in the collection, and the IDictionary has a fixed size.

This property provides the ability to access a specific element in the collection by using the following syntax: myCollection[key].

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.

Implementations can vary in whether they allow the key to be Nothing.

The C# language uses the thisthis (C# Reference) keyword to define the indexers instead of implementing the Item property. Visual Basic implements Item as a default property, which provides the same indexing functionality.

The following code example demonstrates how to implement the Item property. This code example is part of a larger example provided for the IDictionary class.

Public Property Item(ByVal key As Object) As Object Implements IDictionary.Item

        ' If this key is in the dictionary, return its value. 
        Dim index As Integer 
        If TryGetIndexOfKey(key, index) Then 

            ' The key was found return its value. 
            Return items(index).Value

            ' The key was not found return null. 
            Return Nothing 
        End If 
    End Get 

    Set(ByVal value As Object)
        ' If this key is in the dictionary, change its value.  
        Dim index As Integer 
        If TryGetIndexOfKey(key, index) Then 

            ' The key was found change its value.
            items(index).Value = value

            ' This key is not in the dictionary add this key/value pair.
            Add(key, value)
        End If 
    End Set 
End Property

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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