IEqualityComparer<T> 介面


定義支援物件之相等比較的方法。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)



要比較之物件的類型。The type of objects to compare.

這是反變數的型別參數。 也就是說,您可以使用您指定的類型,或衍生程度較低的任何類型。 如需共變數與反變數的詳細資訊,請參閱泛型中的共變數與反變數


下列範例會將自訂 Box 物件新增至字典集合。The following example adds custom Box objects to a dictionary collection. Box如果物件的維度相同,則會將它們視為相等。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.


這個介面可讓您針對集合進行自訂的相等比較。This interface allows the implementation of customized equality comparison for collections. 也就是說,您可以針對型別建立自己的相等定義 T ,並指定這個定義要搭配接受泛型介面的集合型別使用 IEqualityComparer<T>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,泛型集合類型的函式會 Dictionary<TKey,TValue> 接受這個介面。In the .NET Framework, constructors of the Dictionary<TKey,TValue> generic collection type accept this interface.

這個介面的預設執行是由 Default 泛型類別的屬性所提供 EqualityComparer<T>A default implementation of this interface is provided by the Default property of the EqualityComparer<T> generic class. 類別會實作為 StringComparer IEqualityComparer<T> 型別 StringThe StringComparer class implements IEqualityComparer<T> of type String.

這個介面僅支援相等比較。This interface supports only equality comparisons. 自訂排序和排序的比較是由 IComparer<T> 泛型介面提供。Customization of comparisons for sorting and ordering is provided by the IComparer<T> generic interface.

我們建議您從 EqualityComparer<T> 類別衍生而不是實作為 IEqualityComparer<T> 介面,因為類別會 EqualityComparer<T> 使用 IEquatable<T>.Equals 方法(而非方法)來測試是否相等 Object.EqualsWe 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. 這與 Contains IndexOf LastIndexOf Remove Dictionary<TKey,TValue> 類別和其他泛型集合的、、和方法一致。This is consistent with the Contains, IndexOf, LastIndexOf, and Remove methods of the Dictionary<TKey,TValue> class and other generic collections.


Equals(T, T)

判斷指定的物件是否相等。Determines whether the specified objects are equal.


傳回指定物件的雜湊碼。Returns a hash code for the specified object.