IEqualityComparer<T> Interface


定义用于支持比较对象是否相等的方法。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


要比较的对象的类型。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.


下面的示例将自定义 Box 对象添加到字典集合。The following example adds custom Box objects to a dictionary collection. 如果 Box 对象的维度相同,则将它们视为相等。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("The dictionary contains {0} Box objects.",

   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;
            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("The dictionary contains {0} Box objects.",
   End Sub

   Private Sub AddBox(dict As Dictionary(Of Box, String), box As Box, name As String)
         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
            Return _Height
        End Get
        Set(ByVal value As Integer)
            _Height = value
        End Set
    End Property

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

    Public Property Width() As Integer
            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
            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.


此接口允许实现集合的自定义相等性比较。This interface allows the implementation of customized equality comparison for collections. 也就是说,你可以为类型 T创建你自己的相等性定义,并指定此定义与接受 IEqualityComparer<T> 泛型接口的集合类型一起使用。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. 在 .NET Framework 中,Dictionary<TKey,TValue> 泛型集合类型的构造函数接受此接口。In the .NET Framework, constructors of the Dictionary<TKey,TValue> generic collection type accept this interface.

此接口的默认实现由 EqualityComparer<T> 泛型类的 Default 属性提供。A default implementation of this interface is provided by the Default property of the EqualityComparer<T> generic class. StringComparer 类实现 String类型的 IEqualityComparer<T>The StringComparer class implements IEqualityComparer<T> of type String.

此接口仅支持相等比较。This interface supports only equality comparisons. 排序和排序比较的自定义是由 IComparer<T> 泛型接口提供的。Customization of comparisons for sorting and ordering is provided by the IComparer<T> generic interface.

建议从 EqualityComparer<T> 类派生,而不是实现 IEqualityComparer<T> 接口,因为 EqualityComparer<T> 类使用 IEquatable<T>.Equals 方法而不是 Object.Equals 方法来测试是否相等。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. 这与 Dictionary<TKey,TValue> 类和其他泛型集合的 ContainsIndexOfLastIndexOfRemove 方法一致。This is consistent with the Contains, IndexOf, LastIndexOf, and Remove methods of the Dictionary<TKey,TValue> class and other generic collections.


Equals(T, T)

确定指定的对象是否相等。Determines whether the specified objects are equal.


返回指定对象的哈希代码。Returns a hash code for the specified object.

Applies to

See also