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IComparer<T> Interface


Defines a method that a type implements to compare two objects.

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

Public Interface IComparer(Of In T)

Type Parameters

in T

The type of objects to compare.

Name Description
System_CAPS_pubmethod Compare(T, T)

Compares two objects and returns a value indicating whether one is less than, equal to, or greater than the other.

This interface is used with the List<T>.Sort and List<T>.BinarySearch methods. It provides a way to customize the sort order of a collection. Classes that implement this interface include the SortedDictionary<TKey, TValue> and SortedList<TKey, TValue> generic classes.

The default implementation of this interface is the Comparer<T> class. The StringComparer class implements this interface for type String.

This interface supports ordering comparisons. That is, when the Compare method returns 0, it means that two objects sort the same. Implementation of exact equality comparisons is provided by the IEqualityComparer<T> generic interface.

We recommend that you derive from the Comparer<T> class instead of implementing the IComparer<T> interface, because the Comparer<T> class provides an explicit interface implementation of the IComparer.Compare method and the Default property that gets the default comparer for the object.

The following example implements the IComparer<T> interface to compare objects of type Box according to their dimensions. This example is part of a larger example provided for the Comparer<T> class.

' This class is not demonstrated in the Main method
' and is provided only to show how to implement
' the interface. It is recommended to derive
' from Comparer<T> instead of implementing IComparer<T>.
Public Class BoxComp
	Implements IComparer(Of Box)
	' Compares by Height, Length, and Width.
    Public Function Compare(ByVal x As Box, ByVal y As Box) As Integer Implements _
                                                IComparer(Of Box).Compare
        If x.Height.CompareTo(y.Height) <> 0 Then
            Return x.Height.CompareTo(y.Height)
        ElseIf x.Length.CompareTo(y.Length) <> 0 Then
            Return x.Length.CompareTo(y.Length)
        ElseIf x.Width.CompareTo(y.Width) <> 0 Then
            Return x.Width.CompareTo(y.Width)
            Return 0
        End If
    End Function
End Class
Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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