EqualityComparer<T> Classe

  • Riferimento

Definizione

Spazio dei nomi:
System.Collections.Generic
Assembly:
System.Collections.dll
Assembly:
mscorlib.dll
Assembly:
netstandard.dll
Source:
EqualityComparer.CoreCLR.cs
Source:
EqualityComparer.CoreCLR.cs
Source:
EqualityComparer.CoreCLR.cs

Fornisce una classe base per le implementazioni dell'interfaccia generica IEqualityComparer<T>.

generic <typename T>
public ref class EqualityComparer abstract : System::Collections::Generic::IEqualityComparer<T>, System::Collections::IEqualityComparer
public abstract class EqualityComparer<T> : System.Collections.Generic.IEqualityComparer<T>, System.Collections.IEqualityComparer
[System.Serializable]
public abstract class EqualityComparer<T> : System.Collections.Generic.IEqualityComparer<T>, System.Collections.IEqualityComparer
type EqualityComparer<'T> = class
    interface IEqualityComparer<'T>
    interface IEqualityComparer
[<System.Serializable>]
type EqualityComparer<'T> = class
    interface IEqualityComparer
    interface IEqualityComparer<'T>
Public MustInherit Class EqualityComparer(Of T)
Implements IEqualityComparer, IEqualityComparer(Of T)

Parametri di tipo

T

Tipo di oggetti da confrontare.

Ereditarietà
Object
EqualityComparer<T>
Attributi
SerializableAttribute
Implementazioni
IEqualityComparer<T> IEqualityComparer

Esempio

Nell'esempio seguente viene creata una raccolta dizionario di oggetti di tipo Box con un operatore di confronto di uguaglianza. Due caselle sono considerate uguali se le loro dimensioni sono uguali. Aggiunge quindi le caselle all'insieme.

Il dizionario viene ricreato con un operatore di confronto di uguaglianza che definisce l'uguaglianza in modo diverso: due caselle vengono considerate uguali se i volumi sono uguali.

using System;
using System.Collections.Generic;

class Program
{
    static Dictionary<Box, String> boxes;

    static void Main()
    {
        BoxSameDimensions boxDim = new BoxSameDimensions();
        boxes = new Dictionary<Box, string>(boxDim);

        Console.WriteLine("Boxes equality by dimensions:");
        Box redBox = new Box(8, 4, 8);
        Box greenBox = new Box(8, 6, 8);
        Box blueBox = new Box(8, 4, 8);
        Box yellowBox = new Box(8, 8, 8);
        AddBox(redBox, "red");
        AddBox(greenBox, "green");
        AddBox(blueBox, "blue");
        AddBox(yellowBox, "yellow");

        Console.WriteLine();
        Console.WriteLine("Boxes equality by volume:");

        BoxSameVolume boxVolume = new BoxSameVolume();
        boxes = new Dictionary<Box, string>(boxVolume);
        Box pinkBox = new Box(8, 4, 8);
        Box orangeBox = new Box(8, 6, 8);
        Box purpleBox = new Box(4, 8, 8);
        Box brownBox = new Box(8, 8, 4);
        AddBox(pinkBox, "pink");
        AddBox(orangeBox, "orange");
        AddBox(purpleBox, "purple");
        AddBox(brownBox, "brown");
    }

    public static void AddBox(Box bx, string name)
    {
        try
        {
            boxes.Add(bx, name);
            Console.WriteLine("Added {0}, Count = {1}, HashCode = {2}",
                name, boxes.Count.ToString(), bx.GetHashCode());
        }
        catch (ArgumentException)
        {
            Console.WriteLine("A box equal to {0} is already in the collection.", name);
        }
    }
}

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; }
}

class BoxSameDimensions : EqualityComparer<Box>
{
    public override bool Equals(Box b1, Box b2)
    {
        if (b1 == null && b2 == null)
            return true;
        else if (b1 == null || b2 == null)
            return false;

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

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

class BoxSameVolume : EqualityComparer<Box>
{
    public override bool Equals(Box b1, Box b2)
    {
        if (b1 == null && b2 == null)
            return true;
        else if (b1 == null || b2 == null)
            return false;

        return (b1.Height * b1.Width * b1.Length ==
                b2.Height * b2.Width * b2.Length);
    }

    public override int GetHashCode(Box bx)
    {
        int hCode = bx.Height * bx.Length * bx.Width;
        return hCode.GetHashCode();
    }
}
/* This example produces an output similar to the following:
 *
      Boxes equality by dimensions:
      Added red, Count = 1, HashCode = 46104728
      Added green, Count = 2, HashCode = 12289376
      A box equal to blue is already in the collection.
      Added yellow, Count = 3, HashCode = 43495525

      Boxes equality by volume:
      Added pink, Count = 1, HashCode = 55915408
      Added orange, Count = 2, HashCode = 33476626
      A box equal to purple is already in the collection.
      A box equal to brown is already in the collection.
 *
*/

'Imports System.Collections
Imports System.Collections.Generic

Module Program
    Dim boxes As Dictionary(Of Box, [String])

    Public Sub Main(ByVal args As String())

        Dim boxDim As New BoxSameDimensions()
        boxes = New Dictionary(Of Box, String)(boxDim)

        Console.WriteLine("Boxes equality by dimensions:")
        Dim redBox As New Box(8, 4, 8)
        Dim greenBox As New Box(8, 6, 8)
        Dim blueBox As New Box(8, 4, 8)
        Dim yellowBox As New Box(8, 8, 8)
        AddBox(redBox, "red")
        AddBox(greenBox, "green")
        AddBox(blueBox, "blue")
        AddBox(yellowBox, "yellow")

        Console.WriteLine()
        Console.WriteLine("Boxes equality by volume:")

        Dim boxVolume As New BoxSameVolume()
        boxes = New Dictionary(Of Box, String)(boxVolume)
        Dim pinkBox As New Box(8, 4, 8)
        Dim orangeBox As New Box(8, 6, 8)
        Dim purpleBox As New Box(4, 8, 8)
        Dim brownBox As New Box(8, 8, 4)
        AddBox(pinkBox, "pink")
        AddBox(orangeBox, "orange")
        AddBox(purpleBox, "purple")
        AddBox(brownBox, "brown")
    End Sub

    Public Sub AddBox(ByVal bx As Box, ByVal name As String)
        Try
            boxes.Add(bx, name)
            Console.WriteLine("Added {0}, Count = {1}, HashCode = {2}", _
                              name, boxes.Count.ToString(), bx.GetHashCode())
        Catch generatedExceptionName As ArgumentException
            Console.WriteLine("A box equal to {0} is already in the collection.", name)
        End Try
    End Sub
End Module

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

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

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

Class BoxSameDimensions : Inherits EqualityComparer(Of Box)
    Public Overloads Overrides Function Equals(ByVal b1 As Box, _
                                      ByVal b2 As Box) As Boolean
        If b1 Is Nothing AndAlso b2 Is Nothing Then
           Return True
        Else If b1 Is Nothing OrElse b2 Is Nothing Then
           Return False
        End If

        Return (b1.Height = b2.Height AndAlso b1.Length = b2.Length _
                                      AndAlso b1.Width = b2.Width)
    End Function

    Public Overloads Overrides Function GetHashCode(ByVal bx As Box) As Integer
        Dim hCode As Integer = bx.Height Xor bx.Length Xor bx.Width
        Return hCode.GetHashCode()
    End Function
End Class

Class BoxSameVolume : Inherits EqualityComparer(Of Box)
    Public Overloads Overrides Function Equals(ByVal b1 As Box, _
                                          ByVal b2 As Box) As Boolean
        If b1 Is Nothing AndAlso b2 Is Nothing Then
           Return True
        Else If b1 Is Nothing OrElse b2 Is Nothing Then
           Return False
        End If

        Return (b1.Height * b1.Width * b1.Length = _
                b2.Height * b2.Width * b2.Length)
    End Function

    Public Overloads Overrides Function GetHashCode(ByVal bx As Box) As Integer
        Dim hCode As Integer = bx.Height * bx.Length * bx.Width
        Return hCode.GetHashCode()
    End Function
End Class
' This example produces an output similar to the following:
' * 
'    Boxes equality by dimensions:
'    Added red, Count = 1, HashCode = 46104728
'    Added green, Count = 2, HashCode = 12289376
'    A box equal to blue is already in the collection.
'    Added yellow, Count = 3, HashCode = 43495525
'
'    Boxes equality by volume:
'    Added pink, Count = 1, HashCode = 55915408
'    Added orange, Count = 2, HashCode = 33476626
'    A box equal to purple is already in the collection.
'    A box equal to brown is already in the collection.
' * 
'

Commenti

Derivare da questa classe per fornire un'implementazione personalizzata dell'interfaccia IEqualityComparer<T> generica da usare con classi di raccolta, ad esempio la Dictionary<TKey,TValue> classe generica o con metodi come List<T>.Sort.

La Default proprietà controlla se il tipo T implementa l'interfaccia System.IEquatable<T> generica e, in tal caso, restituisce un EqualityComparer<T> oggetto che richiama l'implementazione del IEquatable<T>.Equals metodo . In caso contrario, restituisce un oggetto EqualityComparer<T>, come fornito da T.

In .NET 8 e versioni successive è consigliabile usare il EqualityComparer<T>.Create(Func<T,T,Boolean>, Func<T,Int32>) metodo per creare istanze di questo tipo.

Costruttori

EqualityComparer<T>()

Inizializza una nuova istanza della classe EqualityComparer<T>.

Proprietà

Default

Restituisce un operatore di confronto uguaglianze predefinito per il tipo specificato dall'argomento generico.

Metodi

Create(Func<T,T,Boolean>, Func<T,Int32>)

Crea un EqualityComparer<T> oggetto usando i delegati specificati come implementazione dei metodi e GetHashCode(T) dell'operatore di Equals(T, T) confronto.
Equals(Object)

Determina se l'oggetto specificato è uguale all'oggetto corrente.

(Ereditato da Object)
Equals(T, T)

Quando sottoposto a override in una classe derivata, determina se due oggetti di tipo T sono uguali.
GetHashCode()

Funge da funzione hash predefinita.

(Ereditato da Object)
GetHashCode(T)

Quando ne viene eseguito l'override in una classe derivata, viene usato come funzione hash dell'oggetto specificato per gli algoritmi e le strutture di dati hash, come ad esempio una tabella hash.
GetType()

Ottiene l'oggetto Type dell'istanza corrente.

(Ereditato da Object)
MemberwiseClone()

Crea una copia superficiale dell'oggetto Object corrente.

(Ereditato da Object)
ToString()

Restituisce una stringa che rappresenta l'oggetto corrente.

(Ereditato da Object)

Implementazioni dell'interfaccia esplicita

IEqualityComparer.Equals(Object, Object)

Determina se gli oggetti specificati sono uguali.
IEqualityComparer.GetHashCode(Object)

Viene restituito un codice hash per l'oggetto specificato.

Si applica a

Vedi anche