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IComparer.Compare Method

Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other.

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

'Declaration
Function Compare ( _
	x As Object, _
	y As Object _
) As Integer

Parameters

x
Type: System.Object

The first object to compare.

y
Type: System.Object

The second object to compare.

Return Value

Type: System.Int32
A signed integer that indicates the relative values of x and y, as shown in the following table.

Value

Meaning

Less than zero

x is less than y.

Zero

x equals y.

Greater than zero

x is greater than y.

ExceptionCondition
ArgumentException

Neither x nor y implements the IComparable interface.

-or-

x and y are of different types and neither one can handle comparisons with the other.

The preferred implementation is to use the CompareTo method of one of the parameters.

Comparing Nothing with any type is allowed and does not generate an exception when using IComparable. When sorting, Nothing is considered to be less than any other object.

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

.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

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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