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IComparer Interface

Exposes a method that compares two objects.

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

'Declaration
<ComVisibleAttribute(True)> _
Public Interface IComparer
'Usage
Dim instance As IComparer

This interface is used in conjunction with the Array.Sort and Array.BinarySearch methods. It provides a way to customize the sort order of a collection.

The default implementation of this interface is the Comparer class. For the generic version of this interface, see System.Collections.Generic.IComparer(Of T).

The following code example demonstrates the use of the IComparer interface to sort an ArrayList object. In this example, the IComparer interface is implemented using the CaseInsensitiveComparer class to reverse the order of the contents of the ArrayList.

Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Class SamplesArrayList

   Public Class myReverserClass
      Implements IComparer

      ' Calls CaseInsensitiveComparer.Compare with the parameters reversed. 
      Public Function Compare( ByVal x As Object, ByVal y As Object) As Integer _
         Implements IComparer.Compare
         Return New CaseInsensitiveComparer().Compare(y, x)
      End Function 'IComparer.Compare

   End Class 'myReverserClass

   Public Shared Sub Main()

      ' Creates and initializes a new ArrayList. 
      Dim myAL As New ArrayList()
      myAL.Add("The")
      myAL.Add("quick")
      myAL.Add("brown")
      myAL.Add("fox")
      myAL.Add("jumps")
      myAL.Add("over")
      myAL.Add("the")
      myAL.Add("lazy")
      myAL.Add("dog")

      ' Displays the values of the ArrayList.
      Console.WriteLine("The ArrayList initially contains the following values:")
      PrintIndexAndValues(myAL)

      ' Sorts the values of the ArrayList using the default comparer.
      myAL.Sort()
      Console.WriteLine("After sorting with the default comparer:")
      PrintIndexAndValues(myAL)

      ' Sorts the values of the ArrayList using the reverse case-insensitive comparer. 
      Dim myComparer = New myReverserClass()
      myAL.Sort(myComparer)
      Console.WriteLine("After sorting with the reverse case-insensitive comparer:")
      PrintIndexAndValues(myAL)

   End Sub 'Main

   Public Shared Sub PrintIndexAndValues(myList As IEnumerable)
      Dim i As Integer = 0
      Dim obj As [Object]
      For Each obj In  myList
         Console.WriteLine(vbTab + "[{0}]:" + vbTab + "{1}", i, obj)
         i = i + 1
      Next obj
      Console.WriteLine()
   End Sub 'PrintIndexAndValues

End Class 'SamplesArrayList


'This code produces the following output. 
'The ArrayList initially contains the following values: 
'        [0]:    The 
'        [1]:    quick 
'        [2]:    brown 
'        [3]:    fox 
'        [4]:    jumps 
'        [5]:    over 
'        [6]:    the 
'        [7]:    lazy 
'        [8]:    dog 

'After sorting with the default comparer: 
'        [0]:    brown 
'        [1]:    dog 
'        [2]:    fox 
'        [3]:    jumps 
'        [4]:    lazy 
'        [5]:    over 
'        [6]:    quick 
'        [7]:    the 
'        [8]:    The 

'After sorting with the reverse case-insensitive comparer: 
'        [0]:    the 
'        [1]:    The 
'        [2]:    quick 
'        [3]:    over 
'        [4]:    lazy 
'        [5]:    jumps 
'        [6]:    fox 
'        [7]:    dog 
'        [8]:    brown

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

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