IEqualityComparer<T> Interface

Definition

{1&gt;Define métodos para dar suporte à comparação de objetos para igualdade.&lt;1}Defines methods to support the comparison of objects for equality.

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)

Type Parameters

T

O tipo de objetos a serem comparados.The type of objects to compare.

This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
Derived

Examples

O exemplo a seguir adiciona objetos de Box personalizados a uma coleção de dicionários.The following example adds custom Box objects to a dictionary collection. Os objetos Box são considerados iguais se suas dimensões são as mesmas.The Box objects are considered equal if their dimensions are the same.

using System;
using System.Collections.Generic;

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

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

      var redBox = new Box(4, 3, 4);
      AddBox(boxes, redBox, "red");

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

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

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

   private static void AddBox(Dictionary<Box, String> dict, Box box, String name)
   {
      try {
         dict.Add(box, name);
      }
      catch (ArgumentException e) {
         Console.WriteLine("Unable to add {0}: {1}", box, e.Message);
      }
   }
}

public class Box
{
    public Box(int h,  int l, int w)
    {
        this.Height = h;
        this.Length = l;
        this.Width = w;
    }

    public int Height { get; set; }
    public int Length { get; set; }
    public int Width { get; set; }

    public override String ToString()
    {
       return String.Format("({0}, {1}, {2})", Height, Length, Width);
    }
}

class BoxEqualityComparer : IEqualityComparer<Box>
{
    public bool Equals(Box b1, Box b2)
    {
        if (b2 == null && b1 == null)
           return true;
        else if (b1 == null || b2 == null)
           return false;
        else if(b1.Height == b2.Height && b1.Length == b2.Length
                            && b1.Width == b2.Width)
            return true;
        else
            return false;
    }

    public int GetHashCode(Box bx)
    {
        int hCode = bx.Height ^ bx.Length ^ bx.Width;
        return hCode.GetHashCode();
    }
}
// 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.

Remarks

Essa interface permite a implementação de comparação de igualdade Personalizada para coleções.This interface allows the implementation of customized equality comparison for collections. Ou seja, você pode criar sua própria definição de igualdade para o tipo Te especificar que essa definição seja usada com um tipo de coleção que aceita a interface genérica IEqualityComparer<T>.That is, you can create your own definition of equality for type T, and specify that this definition be used with a collection type that accepts the IEqualityComparer<T> generic interface. No .NET Framework, os construtores do tipo de coleção genérica Dictionary<TKey,TValue> aceitam essa interface.In the .NET Framework, constructors of the Dictionary<TKey,TValue> generic collection type accept this interface.

Uma implementação padrão dessa interface é fornecida pela propriedade Default da classe genérica EqualityComparer<T>.A default implementation of this interface is provided by the Default property of the EqualityComparer<T> generic class. A classe StringComparer implementa IEqualityComparer<T> do tipo String.The StringComparer class implements IEqualityComparer<T> of type String.

Esta interface dá suporte apenas a comparações de igualdade.This interface supports only equality comparisons. A personalização de comparações para classificação e ordenação é fornecida pelo IComparer<T> interface genérica.Customization of comparisons for sorting and ordering is provided by the IComparer<T> generic interface.

É recomendável que você derive da classe EqualityComparer<T> em vez de implementar a interface IEqualityComparer<T>, porque a classe EqualityComparer<T> testa a igualdade usando o método IEquatable<T>.Equals em vez do método Object.Equals.We recommend that you derive from the EqualityComparer<T> class instead of implementing the IEqualityComparer<T> interface, because the EqualityComparer<T> class tests for equality using the IEquatable<T>.Equals method instead of the Object.Equals method. Isso é consistente com os métodos Contains, IndexOf, LastIndexOfe Remove da classe Dictionary<TKey,TValue> e outras coleções genéricas.This is consistent with the Contains, IndexOf, LastIndexOf, and Remove methods of the Dictionary<TKey,TValue> class and other generic collections.

Methods

Equals(T, T)

Determina se os objetos especificados são iguais.Determines whether the specified objects are equal.

GetHashCode(T)

Retorna um código hash para o objeto especificado.Returns a hash code for the specified object.

Applies to

See also