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IComparer Interface

Exposes a method that compares two objects.

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

[ComVisibleAttribute(true)] 
public interface class IComparer
/** @attribute ComVisibleAttribute(true) */ 
public interface IComparer
ComVisibleAttribute(true) 
public interface IComparer
Not applicable.

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.

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 ) = 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 
*/

import System.*;
import System.Collections.*;

public class SamplesArrayList
{
    public static class MyReverserClass implements IComparer
    {
        // Calls CaseInsensitiveComparer.Compare with the parameters reversed.
        public int Compare(Object x, Object y)
        {
            return(new CaseInsensitiveComparer()).Compare(y, x) ;
        } //IComparer.Compare
    } //MyReverserClass
    
    public static void main(String[] args) 
    {
        // 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);
    } //main
       
    public static void PrintIndexAndValues(IEnumerable myList) 
    {
        int i = 0;
        IEnumerator objEnum = myList.GetEnumerator();
        while (objEnum.MoveNext()) {
            Object obj = objEnum.get_Current();
            Console.WriteLine("\t[{0}]:\t{1}",(Int32)i++, obj);
        }
        Console.WriteLine();
    } //PrintIndexAndValues
} //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 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0
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