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

定义

指示当前对象是否等于同一类型的另一个对象。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

参数

other

一个与此对象进行比较的对象。An object to compare with this object.

返回

如果当前对象等于 other 参数,则为 true;否则为 falsetrue if the current object is equal to the other parameter; otherwise, false.

示例

下面Person的示例演示实现IEquatable<T>并具有两个属性 (和SSN) LastName的类的分部实现。The following example shows the partial implementation of a Person class that implements IEquatable<T> and has two properties, LastName and SSN. 如果Equals两个True对象的 SSN属性相同,False则该方法返回; 否则返回。 PersonThe 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

Person然后, 可以将对象存储在List<T>对象中, 并可Contains通过方法进行标识, 如下面的示例所示。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.

注解

Equals方法的实现旨在执行与类型T的另一个对象相等的测试, 与当前对象的类型相同。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. Equals(T)方法在以下情况下调用:The Equals(T) method is called in the following circumstances:

换句话说, 若要处理某个类的对象将存储在数组或泛型集合对象中的可能性, 最好实现IEquatable<T>此方法, 以便能够轻松地标识和操作该对象。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.

实现Equals方法时, 请为泛型类型参数指定的类型适当地定义相等性。When implementing the Equals method, define equality appropriately for the type specified by the generic type argument. 例如, 如果类型参数为Int32, 则为 2 32 位有符号整数的比较适当地定义相等性。For example, if the type argument is Int32, define equality appropriately for the comparison of two 32-bit signed integers.

实施者说明

如果实现Equals(T), 则还应重写Equals(Object)GetHashCode()的基类实现, 以使Equals(T)它们的行为与方法的行为一致。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. 如果确实要重Equals(Object)写, 则也会在对类的静态Equals(System.Object, System.Object)方法的调用中调用重写的实现。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. 此外, 还应重载op_Equalityop_Inequality运算符。In addition, you should overload the op_Equality and op_Inequality operators. 这可确保所有相等测试都返回一致的结果, 如示例所示。This ensures that all tests for equality return consistent results, which the example illustrates.

适用于