Add Method (TKey, TValue)
Collapse the table of content
Expand the table of content

IDictionary(Of TKey, TValue).Add Method (TKey, TValue)

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Adds an element with the provided key and value to the IDictionary(Of TKey, TValue).

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

'Declaration
Sub Add ( _
	key As TKey, _
	value As TValue _
)

Parameters

key
Type: TKey
The object to use as the key of the element to add.
value
Type: TValue
The object to use as the value of the element to add.

ExceptionCondition
ArgumentNullException

key is Nothing.

ArgumentException

An element with the same key already exists in the IDictionary(Of TKey, TValue).

NotSupportedException

The IDictionary(Of TKey, TValue) is read-only.

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 in C# (myCollection("myNonexistentKey") = myValue in Visual Basic). 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 how they determine equality of objects; for example, the List(Of T) class uses Comparer(Of T).Default, whereas the Dictionary(Of TKey, TValue) class allows the user to specify the IComparer(Of T) implementation to use for comparing keys.

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

The following code example creates an empty Dictionary(Of TKey, TValue) of strings, with integer keys, and accesses it through the IDictionary(Of TKey, TValue) interface. The code example 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 is part of a larger example that can be compiled and executed. See System.Collections.Generic.IDictionary(Of TKey, TValue).


' Create a new dictionary of strings, with string keys, 
' and access it through the IDictionary generic interface.
Dim openWith As IDictionary(Of String, String) = _
    New Dictionary(Of 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
   outputBlock.Text &= "An element with Key = ""txt"" already exists." & vbCrLf
End Try


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

Show:
© 2017 Microsoft