IEquatable<T>.Equals(T) IEquatable<T>.Equals(T) IEquatable<T>.Equals(T) IEquatable<T>.Equals(T) Method

Definizione

Indica se l'oggetto corrente è uguale a un altro oggetto dello stesso tipo.Indicates whether the current object is equal to another object of the same type.

public:
 bool Equals(T other);
public bool Equals (T other);
abstract member Equals : 'T -> bool
Public Function Equals (other As T) As Boolean

Parametri

other

Oggetto da confrontare con l'oggetto corrente.An object to compare with this object.

Restituisce

true se l'oggetto corrente è uguale al parametro other; in caso contrario, false.true if the current object is equal to the other parameter; otherwise, false.

Esempi

Nell'esempio seguente viene illustrata l'implementazione parziale Person di una classe IEquatable<T> che implementa e dispone di LastName due SSNproprietà, e.The following example shows the partial implementation of a Person class that implements IEquatable<T> and has two properties, LastName and SSN. Il Equals metodo restituisce True se la SSN proprietà di due Person oggetti è identica; in caso contrario, Falserestituisce.The Equals method returns True if the SSN property of two Person objects is identical; otherwise, it returns False.

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

public class Person : IEquatable<Person>
{
   private string uniqueSsn;
   private string lName;

   public Person(string lastName, string ssn)
   {
      if (Regex.IsMatch(ssn, @"\d{9}"))
        uniqueSsn = $"{ssn.Substring(0, 3)}-{ssn.Substring(3, 2)}-{ssn.Substring(5, 4)}";
      else if (Regex.IsMatch(ssn, @"\d{3}-\d{2}-\d{4}"))
         uniqueSsn = ssn;
      else
         throw new FormatException("The social security number has an invalid format.");

      this.LastName = lastName;
   }

   public string SSN
   {
      get { return this.uniqueSsn; }
   }

   public string LastName
   {
      get { return this.lName; }
      set {
         if (String.IsNullOrEmpty(value))
            throw new ArgumentException("The last name cannot be null or empty.");
         else
            this.lName = value;
      }
   }

   public bool Equals(Person other)
   {
      if (other == null)
         return false;

      if (this.uniqueSsn == other.uniqueSsn)
         return true;
      else
         return false;
   }

   public override bool Equals(Object obj)
   {
      if (obj == null)
         return false;

      Person personObj = obj as Person;
      if (personObj == null)
         return false;
      else
         return Equals(personObj);
   }

   public override int GetHashCode()
   {
      return this.SSN.GetHashCode();
   }

   public static bool operator == (Person person1, Person person2)
   {
      if (((object)person1) == null || ((object)person2) == null)
         return Object.Equals(person1, person2);

      return person1.Equals(person2);
   }

   public static bool operator != (Person person1, Person person2)
   {
      if (((object)person1) == null || ((object)person2) == null)
         return ! Object.Equals(person1, person2);

      return ! (person1.Equals(person2));
   }
}
Imports System.Collections.Generic
Imports System.Text.RegularExpressions

Public Class Person : Implements IEquatable(Of Person)
   Private uniqueSsn As String
   Private lName As String
   
   Public Sub New(lastName As String, ssn As String)
      If Regex.IsMatch(ssn, "\d{9}") Then
         uniqueSsn = $"{ssn.Substring(0, 3)}-{ssn.Substring(3, 2)}-{ssn.Substring(5, 4)}"
      ElseIf Regex.IsMatch(ssn, "\d{3}-\d{2}-\d{4}") Then
         uniqueSsn = ssn
      Else 
         Throw New FormatException("The social security number has an invalid format.")
      End If
      Me.LastName = lastName
   End Sub
   
   Public ReadOnly Property SSN As String
      Get
         Return Me.uniqueSsn
      End Get      
   End Property
   
   Public Property LastName As String
      Get
         Return Me.lName
      End Get
      Set
         If String.IsNullOrEmpty(value) Then
            Throw New ArgumentException("The last name cannot be null or empty.")
         Else
            lname = value
         End If   
      End Set
   End Property
   
   Public Overloads Function Equals(other As Person) As Boolean _
                   Implements IEquatable(Of Person).Equals
      If other Is Nothing Then Return False
      
      If Me.uniqueSsn = other.uniqueSsn Then
         Return True
      Else
         Return False
      End If
   End Function

   Public Overrides Function Equals(obj As Object) As Boolean
      If obj Is Nothing Then Return False
      
      Dim personObj As Person = TryCast(obj, Person)
      If personObj Is Nothing Then
         Return False
      Else   
         Return Equals(personObj)   
      End If
   End Function   
   
   Public Overrides Function GetHashCode() As Integer
      Return Me.SSN.GetHashCode()
   End Function
   
   Public Shared Operator = (person1 As Person, person2 As Person) As Boolean
      If person1 Is Nothing OrElse person2 Is Nothing Then
         Return Object.Equals(person1, person2)
      End If
         
      Return person1.Equals(person2)
   End Operator
   
   Public Shared Operator <> (person1 As Person, person2 As Person) As Boolean
      If person1 Is Nothing OrElse person2 Is Nothing Then
         Return Not Object.Equals(person1, person2) 
      End If
      
      Return Not person1.Equals(person2)
   End Operator
End Class

Persongli oggetti possono quindi essere archiviati in List<T> un oggetto e possono essere identificati Contains dal metodo, come illustrato nell'esempio riportato di seguito.Person objects can then be stored in a List<T> object and can be identified by the Contains method, as the following example shows.

public class TestIEquatable
{
   public static void Main()
   {
      // Create a Person object for each job applicant.
      Person applicant1 = new Person("Jones", "099-29-4999");
      Person applicant2 = new Person("Jones", "199-29-3999");
      Person applicant3 = new Person("Jones", "299-49-6999");

      // Add applicants to a List object.
      List<Person> applicants = new List<Person>();
      applicants.Add(applicant1);
      applicants.Add(applicant2);
      applicants.Add(applicant3);

       // Create a Person object for the final candidate.
       Person candidate = new Person("Jones", "199-29-3999");
       if (applicants.Contains(candidate))
          Console.WriteLine("Found {0} (SSN {1}).", 
                             candidate.LastName, candidate.SSN);
      else
         Console.WriteLine("Applicant {0} not found.", candidate.SSN);

      // Call the shared inherited Equals(Object, Object) method.
      // It will in turn call the IEquatable(Of T).Equals implementation.
      Console.WriteLine("{0}({1}) already on file: {2}.",  
                        applicant2.LastName, 
                        applicant2.SSN, 
                        Person.Equals(applicant2, candidate)); 
   }
}
// The example displays the following output:
//       Found Jones (SSN 199-29-3999).
//       Jones(199-29-3999) already on file: True.
Module TestIEquatable
   Public Sub Main()
      ' Create a Person object for each job applicant.
      Dim applicant1 As New Person("Jones", "099-29-4999")
      Dim applicant2 As New Person("Jones", "199-29-3999")
      Dim applicant3 As New Person("Jones", "299-49-6999")

      ' Add applicants to a List object.
      Dim applicants As New List(Of Person)
      applicants.Add(applicant1)
      applicants.Add(applicant2)
      applicants.Add(applicant3)
      
      ' Create a Person object for the final candidate.
      Dim candidate As New Person("Jones", "199-29-3999")
      
      If applicants.Contains(candidate) Then
         Console.WriteLine("Found {0} (SSN {1}).", _
                            candidate.LastName, candidate.SSN)
      Else
         Console.WriteLine("Applicant {0} not found.", candidate.SSN)
      End If         

      ' Call the shared inherited Equals(Object, Object) method.
      ' It will in turn call the IEquatable(Of T).Equals implementation.
      Console.WriteLine("{0}({1}) already on file: {2}.", _ 
                        applicant2.LastName, _
                        applicant2.SSN, _
                        Person.Equals(applicant2, candidate)) 
   End Sub
End Module
' The example displays the following output:
'       Found Jones (SSN 199-29-3999).
'       Jones(199-29-3999) already on file: True.

Commenti

L'implementazione del Equals metodo è progettata per eseguire un test di uguaglianza con un altro oggetto di tipo T, dello stesso tipo dell'oggetto corrente.The implementation of the Equals method is intended to perform a test for equality with another object of type T, the same type as the current object. Il Equals(T) metodo viene chiamato nelle circostanze seguenti:The Equals(T) method is called in the following circumstances:

In altre parole, per gestire la possibilità che gli oggetti di una classe vengano archiviati in una matrice o in un oggetto raccolta generico, è consigliabile implementare IEquatable<T> in modo che l'oggetto possa essere facilmente identificato e modificato.In other words, to handle the possibility that objects of a class will be stored in an array or a generic collection object, it is a good idea to implement IEquatable<T> so that the object can be easily identified and manipulated.

Quando si implementa Equals il metodo, definire l'uguaglianza in modo appropriato per il tipo specificato dall'argomento di tipo generico.When implementing the Equals method, define equality appropriately for the type specified by the generic type argument. Se, ad esempio, l'argomento di Int32tipo è, definire l'uguaglianza in modo appropriato per il confronto di interi con segno a 2 32 bit.For example, if the type argument is Int32, define equality appropriately for the comparison of two 32-bit signed integers.

Note per gli implementatori

Se si implementa Equals(T), è necessario anche eseguire l'override delle implementazioni della Equals(Object) classe GetHashCode() di base di e in modo che il Equals(T) loro comportamento sia coerente con quello del metodo.If you implement Equals(T), you should also override the base class implementations of Equals(Object) and GetHashCode() so that their behavior is consistent with that of the Equals(T) method. Se si esegue l' Equals(Object)override di, l'implementazione sottoposta a override viene chiamata anche Equals(System.Object, System.Object) nelle chiamate al metodo statico sulla classe.If you do override Equals(Object), your overridden implementation is also called in calls to the static Equals(System.Object, System.Object) method on your class. Inoltre, è necessario eseguire l'overload op_Equality degli op_Inequality operatori e.In addition, you should overload the op_Equality and op_Inequality operators. Ciò garantisce che tutti i test per l'uguaglianza restituiscano risultati coerenti, illustrati nell'esempio.This ensures that all tests for equality return consistent results, which the example illustrates.

Si applica a