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11/17/2011

IComparable Interface

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Defines a generalized type-specific comparison method that a value type or class implements to order or sort its instances.

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

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public Interface IComparable

[ComVisibleAttribute(true)]
public interface IComparable

The IComparable type exposes the following members.

Methods

	Name	Description
	CompareTo	Compares the current instance with another object of the same type and returns an integer that indicates whether the current instance precedes, follows, or occurs in the same position in the sort order as the other object.

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Remarks

This interface is implemented by types whose values can be ordered or sorted. It requires that implementing types define a single method, CompareTo, that indicates whether the position of the current instance in the sort order is before, after, or the same as a second object of the same type. The instance's IComparable implementation is called automatically by methods such as Array.Sort.

All numeric types (such as Int32 and Double) implement IComparable, as do String, Char, and DateTime. Custom types should also provide their own implementation of IComparable to allow object instances to be ordered or sorted.

Examples

The following code sample illustrates the implementation of IComparable and the requisite CompareTo method.

Imports System.Collections

Public Class Temperature
   Implements IComparable
   ' The temperature value
   Protected temperatureF As Double

   Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
       Implements IComparable.CompareTo

      If obj Is Nothing Then Return 1

      Dim otherTemperature As Temperature = TryCast(obj, Temperature)
      If otherTemperature IsNot Nothing Then
         Return Me.temperatureF.CompareTo(otherTemperature.temperatureF)
      Else
         Throw New ArgumentException("Object is not a Temperature")
      End If
   End Function

   Public Property Fahrenheit() As Double
      Get
         Return temperatureF
      End Get
      Set(ByVal Value As Double)
         Me.temperatureF = Value
      End Set
   End Property

   Public Property Celsius() As Double
      Get
         Return (temperatureF - 32) * (5 / 9)
      End Get
      Set(ByVal Value As Double)
         Me.temperatureF = (Value * 9 / 5) + 32
      End Set
   End Property
End Class

Public Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim temperatures(9) As Temperature
      ' Initialize random number generator.
      Dim rnd As New Random()

      ' Generate 10 temperatures between 0 and 100 randomly.
      For ctr As Integer = 1 To 10
         Dim degrees As Integer = rnd.Next(0, 100)
         Dim temp As New Temperature
         temp.Fahrenheit = degrees
         temperatures(ctr - 1) = temp
      Next

      ' Sort Array.
      Array.Sort(temperatures)

      For Each temp As Temperature In temperatures
         outputBlock.Text &= temp.Fahrenheit & vbCrLf
      Next
   End Sub
End Module
' The example displays the following output (individual
' values may vary because they are randomly generated):
'       2
'       7
'       16
'       17
'       31
'       37
'       58
'       66
'       72
'       95

using System;
using System.Collections;

public class Temperature : IComparable
{
   // The temperature value
   protected double temperatureF;

   public int CompareTo(object obj)
   {
      if (obj == null) return 1;

      Temperature otherTemperature = obj as Temperature;
      if (otherTemperature != null)
         return this.temperatureF.CompareTo(otherTemperature.temperatureF);
      else
         throw new ArgumentException("Object is not a Temperature");
   }

   public double Fahrenheit
   {
      get
      {
         return this.temperatureF;
      }
      set
      {
         this.temperatureF = value;
      }
   }

   public double Celsius
   {
      get
      {
         return (this.temperatureF - 32) * (5.0 / 9);
      }
      set
      {
         this.temperatureF = (value * 9.0 / 5) + 32;
      }
   }
}

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      Temperature[] temperatures = new Temperature[10];
      // Initialize random number generator.
      Random rnd = new Random();

      // Generate 10 temperatures between 0 and 100 randomly.
      for (int ctr = 1; ctr <= 10; ctr++)
      {
         int degrees = rnd.Next(0, 100);
         Temperature temp = new Temperature();
         temp.Fahrenheit = degrees;
         temperatures[ctr - 1] = temp;
      }

      // Sort ArrayList.
      Array.Sort(temperatures);

      foreach (Temperature temp in temperatures)
         outputBlock.Text += temp.Fahrenheit + "\n";

   }
}
// The example displays the following output (individual
// values may vary because they are randomly generated):
//       2
//       7
//       16
//       17
//       31
//       37
//       58
//       66
//       72
//       95

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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