ArrayList.Sort Method (IComparer)


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Sorts the elements in the entire ArrayList using the specified comparer.

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

Public Overridable Sub Sort (
	comparer As IComparer


Type: System.Collections.IComparer

The IComparer implementation to use when comparing elements.


A null reference (Nothing in Visual Basic) to use the IComparable implementation of each element.

Exception Condition

The ArrayList is read-only.


An error occurred while comparing two elements.


null is passed for comparer, and the elements in the list do not implement IComparable.

Use the Sort method to sort a list of objects with a custom comparer that implements the IComparer interface. If you pass null for comparer, this method uses the IComparable implementation of each element. In this case, you must make sure that the objects contained in the list implement the IComparer interface or an exception will occur.

In addition, using the IComparable implementation means the list performs a comparison sort (also called an unstable sort); that is, if two elements are equal, their order might not be preserved. In contrast, a stable sort preserves the order of elements that are equal. To perform a stable sort, you must implement a custom IComparer interface.

On average, this method is an O(n log n) operation, where n is Count; in the worst case it is an O(n^2) operation.

The following code example shows how to sort the values in an ArrayList using the default comparer and a custom comparer that reverses the sort order.

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()

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

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

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

   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
   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

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
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