IEqualityComparer<T> Interface

Definition

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

Derived

Microsoft.Extensions.Primitives.StringSegmentComparer

System.StringComparer

System.UriTemplateEquivalenceComparer

System.Collections.Generic.EqualityComparer<T>

System.Collections.Generic.ReferenceEqualityComparer

System.Data.DataRowComparer<TRow>

System.Reflection.Metadata.HandleComparer

System.Xml.Linq.XNodeEqualityComparer

Examples

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();

      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

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 Contains、IndexOf、LastIndexOf和 Remove 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.

Methods

Applies to

See also

• EqualityComparer<T>
• Dictionary<TKey,TValue>
• Dictionary<TKey,TValue>
• IComparer<T>