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Dictionary(Of TKey, TValue) Constructor (Int32, IEqualityComparer(Of TKey))

Initializes a new instance of the Dictionary(Of TKey, TValue) class that is empty, has the specified initial capacity, and uses the specified IEqualityComparer(Of T).

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

'Declaration
Public Sub New ( _
	capacity As Integer, _
	comparer As IEqualityComparer(Of TKey) _
)

Parameters

capacity
Type: System.Int32

The initial number of elements that the Dictionary(Of TKey, TValue) can contain.

comparer
Type: System.Collections.Generic.IEqualityComparer(Of TKey)

The IEqualityComparer(Of T) implementation to use when comparing keys, or Nothing to use the default EqualityComparer(Of T) for the type of the key.

ExceptionCondition
ArgumentOutOfRangeException

capacity is less than 0.

Use this constructor with the case-insensitive string comparers provided by the StringComparer class to create dictionaries with case-insensitive string keys.

Every key in a Dictionary(Of TKey, TValue) must be unique according to the specified comparer.

The capacity of a Dictionary(Of TKey, TValue) is the number of elements that can be added to the Dictionary(Of TKey, TValue) before resizing is necessary. As elements are added to a Dictionary(Of TKey, TValue), the capacity is automatically increased as required by reallocating the internal array.

If the size of the collection can be estimated, specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Dictionary(Of TKey, TValue).

Dictionary(Of TKey, TValue) requires an equality implementation to determine whether keys are equal. If comparer is Nothing, this constructor uses the default generic equality comparer, EqualityComparer(Of T).Default. If type TKey implements the System.IEquatable(Of T) generic interface, the default equality comparer uses that implementation.

This constructor is an O(1) operation.

The following code example creates a Dictionary(Of TKey, TValue) with an initial capacity of 5 and a case-insensitive equality comparer for the current culture. The example adds four elements, some with lower-case keys and some with upper-case keys. The example then attempts to add an element with a key that differs from an existing key only by case, catches the resulting exception, and displays an error message. Finally, the example displays the elements in the dictionary.

Imports System
Imports System.Collections.Generic

Public Class Example

    Public Shared Sub Main() 

        ' Create a new Dictionary of strings, with string keys, an 
        ' initial capacity of 5, and a case-insensitive equality 
        ' comparer. 
        Dim openWith As New Dictionary(Of String, String)(5, _
            StringComparer.CurrentCultureIgnoreCase)

        ' Add 4 elements to the dictionary. 
        openWith.Add("txt", "notepad.exe")
        openWith.Add("bmp", "paint.exe")
        openWith.Add("DIB", "paint.exe")
        openWith.Add("rtf", "wordpad.exe")

        ' Try to add a fifth element with a key that is the same  
        ' except for case; this would be allowed with the default 
        ' comparer. 
        Try
            openWith.Add("BMP", "paint.exe")
        Catch ex As ArgumentException
            Console.WriteLine(vbLf & "BMP is already in the dictionary.")
        End Try 

        ' List the contents of the dictionary.
        Console.WriteLine()
        For Each kvp As KeyValuePair(Of String, String) In openWith
            Console.WriteLine("Key = {0}, Value = {1}", _
                kvp.Key, kvp.Value)
        Next kvp

    End Sub 

End Class 

' This code example produces the following output: 

'BMP is already in the dictionary. 

'Key = txt, Value = notepad.exe 
'Key = bmp, Value = paint.exe 
'Key = DIB, Value = paint.exe 
'Key = rtf, Value = wordpad.exe

.NET Framework

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

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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