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IComparable Interface

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

The IComparable type exposes the following members.

  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCompareToCompares 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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This interface is implemented by types whose values can be ordered or sorted. It requires that implementing types define a single method, CompareTo(Object), 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 and ArrayList.Sort.

The implementation of the CompareTo(Object) method must return an Int32 that has one of three values, as shown in the following table.

Value

Meaning

Less than zero

The current instance precedes the object specified by the CompareTo method in the sort order.

Zero

This current instance occurs in the same position in the sort order as the object specified by the CompareTo method.

Greater than zero

This current instance follows the object specified by the CompareTo method in the sort order.

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 enable object instances to be ordered or sorted.

The following example 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 CompareTemperatures
   Public Sub Main()
      Dim temperatures As New ArrayList
      ' 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.Add(temp)   
      Next 

      ' Sort ArrayList.
      temperatures.Sort()

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

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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