IEqualityComparer<T> Interface

Définition

generic <typename T>
public interface class IEqualityComparer

public interface IEqualityComparer<in T>

public interface IEqualityComparer<T>

type IEqualityComparer<'T> = interface

Public Interface IEqualityComparer(Of In T)

Public Interface IEqualityComparer(Of T)

Paramètres de type

Dérivé

Microsoft.Extensions.Primitives.StringSegmentComparer

System.Collections.Generic.EqualityComparer<T>

System.Collections.Generic.ReferenceEqualityComparer

System.Data.DataRowComparer<TRow>

System.Numerics.TotalOrderIeee754Comparer<T>

Plus…

Exemples

L’exemple suivant ajoute des objets personnalisés Box à une collection de dictionnaires. Les Box objets sont considérés comme égaux si leurs dimensions sont les mêmes.

using System;
using System.Collections.Generic;

static class Example
{
    static void Main()
    {
        BoxEqualityComparer comparer = new();

        Dictionary<Box, string> boxes = new(comparer);

        AddBox(new Box(4, 3, 4), "red");
        AddBox(new Box(4, 3, 4), "blue");
        AddBox(new Box(3, 4, 3), "green");

        Console.WriteLine($"The dictionary contains {boxes.Count} Box objects.");

        void AddBox(Box box, string name)
        {
            try
            {
                boxes.Add(box, name);
            }
            catch (ArgumentException e)
            {
                Console.WriteLine($"Unable to add {box}: {e.Message}");
            }
        }
    }
}

class Box
{
    public int Height { get; }
    public int Length { get; }
    public int Width { get; }

    public Box(int height, int length, int width)
    {
        Height = height;
        Length = length;
        Width = width;
    }

    public override string ToString() => $"({Height}, {Length}, {Width})";
}

class BoxEqualityComparer : IEqualityComparer<Box>
{
    public bool Equals(Box? b1, Box? b2)
    {
        if (ReferenceEquals(b1, b2))
            return true;

        if (b2 is null || b1 is null)
            return false;

        return b1.Height == b2.Height
            && b1.Length == b2.Length
            && b1.Width == b2.Width;
    }

    public int GetHashCode(Box box) => box.Height ^ box.Length ^ box.Width;
}

// The example displays the following output:
//    Unable to add (4, 3, 4): An item with the same key has already been added.
//    The dictionary contains 2 Box objects.

Imports System.Collections.Generic

Module Example
   Public Sub Main()

      Dim boxEqC As New BoxEqualityComparer()

      Dim boxes As New Dictionary(Of Box, String)(boxEqC)

      Dim redBox = New Box(4, 3, 4)
      AddBox(boxes, redBox, "red")

      Dim blueBox = new Box(4, 3, 4)
      AddBox(boxes, blueBox, "blue")

      Dim greenBox = new Box(3, 4, 3)
      AddBox(boxes, greenBox, "green")
      Console.WriteLine()

      Console.WriteLine("The dictionary contains {0} Box objects.",
                        boxes.Count)
   End Sub

   Private Sub AddBox(dict As Dictionary(Of Box, String), box As Box, name As String)
      Try
         dict.Add(box, name)
      Catch e As ArgumentException
         Console.WriteLine("Unable to add {0}: {1}", box, e.Message)
      End Try
   End Sub
End Module

Public Class Box
    Private _Height As Integer
    Private _Length As Integer
    Private _Width As Integer

    Public Sub New(ByVal h As Integer, ByVal l As Integer,
                                        ByVal w As Integer)
        Me.Height = h
        Me.Length = l
        Me.Width = w
    End Sub

    Public Property Height() As Integer
        Get
            Return _Height
        End Get
        Set(ByVal value As Integer)
            _Height = value
        End Set
    End Property

    Public Property Length() As Integer
        Get
            Return _Length
        End Get
        Set(ByVal value As Integer)
            _Length = value
        End Set
    End Property

    Public Property Width() As Integer
        Get
            Return _Width
        End Get
        Set(ByVal value As Integer)
            _Width = value
        End Set
    End Property

    Public Overrides Function ToString() As String
       Return String.Format("({0}, {1}, {2})", _Height, _Length, _Width)
    End Function
End Class

Class BoxEqualityComparer
    Implements IEqualityComparer(Of Box)

    Public Overloads Function Equals(ByVal b1 As Box, ByVal b2 As Box) _
                   As Boolean Implements IEqualityComparer(Of Box).Equals

        If b1 Is Nothing AndAlso b2 Is Nothing Then
            Return True
        ElseIf b1 Is Nothing Or b2 Is Nothing Then
            Return False
        ElseIf b1.Height = b2.Height AndAlso b1.Length =
                b2.Length AndAlso b1.Width = b2.Width Then
            Return True
        Else
            Return False
        End If
    End Function

    Public Overloads Function GetHashCode(ByVal bx As Box) _
                As Integer Implements IEqualityComparer(Of Box).GetHashCode
        Dim hCode As Integer = bx.Height Xor bx.Length Xor bx.Width
        Return hCode.GetHashCode()
    End Function

End Class
' The example displays the following output:
'    Unable to add (4, 3, 4): An item with the same key has already been added.
'
'    The dictionary contains 2 Box objects.

Remarques

Cette interface permet l’implémentation d’une comparaison d’égalité personnalisée pour les collections. Autrement dit, vous pouvez créer votre propre définition d’égalité pour le type Tet spécifier que cette définition doit être utilisée avec un type de collection qui accepte l’interface IEqualityComparer<T> générique. Dans le .NET Framework, les constructeurs du Dictionary<TKey,TValue> type de collection générique acceptent cette interface.

Une implémentation par défaut de cette interface est fournie par la Default propriété de la EqualityComparer<T> classe générique. La StringComparer classe implémente IEqualityComparer<T> de type String.

Cette interface prend uniquement en charge les comparaisons d’égalité. La personnalisation des comparaisons pour le tri et l’ordre est fournie par l’interface IComparer<T> générique.

Nous vous recommandons de dériver de la EqualityComparer<T> classe au lieu d’implémenter l’interface IEqualityComparer<T> , car la EqualityComparer<T> classe teste l’égalité à l’aide de la IEquatable<T>.Equals méthode au lieu de la Object.Equals méthode. Cela est cohérent avec les Containsméthodes , IndexOf, LastIndexOfet Remove de la Dictionary<TKey,TValue> classe et d’autres collections génériques.

Méthodes

S’applique à

Voir aussi

• EqualityComparer<T>
• Dictionary<TKey,TValue>
• Dictionary<TKey,TValue>
• IComparer<T>