IComparer Interface
Definition
Exposes a method that compares two objects.
[System.Runtime.InteropServices.ComVisible(true)]
public interface IComparer
- Derived
- Attributes
Examples
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.
using namespace System;
using namespace System::Collections;
void PrintIndexAndValues( IEnumerable^ myList );
ref class myReverserClass: public IComparer
{
private:
// Calls CaseInsensitiveComparer.Compare with the parameters reversed.
virtual int Compare( Object^ x, Object^ y ) sealed = IComparer::Compare
{
return ((gcnew CaseInsensitiveComparer)->Compare( y, x ));
}
};
int main()
{
// Creates and initializes a new ArrayList.
ArrayList^ myAL = gcnew 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.
IComparer^ myComparer = gcnew myReverserClass;
myAL->Sort( myComparer );
Console::WriteLine( "After sorting with the reverse case-insensitive comparer:" );
PrintIndexAndValues( myAL );
}
void PrintIndexAndValues( IEnumerable^ myList )
{
int i = 0;
IEnumerator^ myEnum = myList->GetEnumerator();
while ( myEnum->MoveNext() )
{
Object^ obj = safe_cast<Object^>(myEnum->Current);
Console::WriteLine( "\t[{0}]:\t{1}", i++, obj );
}
Console::WriteLine();
}
/*
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
*/
using System;
using System.Collections;
public class SamplesArrayList {
public class myReverserClass : IComparer {
// Calls CaseInsensitiveComparer.Compare with the parameters reversed.
int IComparer.Compare( Object x, Object y ) {
return( (new CaseInsensitiveComparer()).Compare( y, x ) );
}
}
public static void Main() {
// Creates and initializes a new ArrayList.
ArrayList myAL = 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.
IComparer myComparer = new myReverserClass();
myAL.Sort( myComparer );
Console.WriteLine( "After sorting with the reverse case-insensitive comparer:" );
PrintIndexAndValues( myAL );
}
public static void PrintIndexAndValues( IEnumerable myList ) {
int i = 0;
foreach ( Object obj in myList )
Console.WriteLine( "\t[{0}]:\t{1}", i++, obj );
Console.WriteLine();
}
}
/*
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
*/
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
Remarks
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. See the Compare method for notes on parameters and return value.
The default implementation of this interface is the Comparer class. For the generic version of this interface, see IComparer<T>.
Methods
| Compare(Object, Object) |
Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other. |