IDictionary.Add Method (Object, Object)


Adds an element with the provided key and value to the IDictionary object.

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

Sub Add (
	key As Object,
	value As Object


Type: System.Object

The Object to use as the key of the element to add.

Type: System.Object

The Object to use as the value of the element to add.

Exception Condition

key is null.


An element with the same key already exists in the IDictionary object.


The IDictionary is read-only.


The IDictionary has a fixed size.

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 null.

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

Public Sub Add(ByVal key As Object, ByVal value As Object) Implements IDictionary.Add

    ' Add the new key/value pair even if this key already exists in the dictionary.
    If ItemsInUse = items.Length Then
        Throw New InvalidOperationException("The dictionary cannot hold any more items.")
    End If
    items(ItemsInUse) = New DictionaryEntry(key, value)
    ItemsInUse = ItemsInUse + 1
End Sub

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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