IEqualityComparer<T> 接口
定义
重要
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定义用于支持比较对象是否相等的方法。
generic <typename T>
public interface class IEqualityComparerpublic interface IEqualityComparer<in T>public interface IEqualityComparer<T>type IEqualityComparer<'T> = interfacePublic Interface IEqualityComparer(Of In T)Public Interface IEqualityComparer(Of T)类型参数
- 派生
示例
以下示例将自定义 Box 对象添加到字典集合。 Box如果对象的尺寸相同，则视为相等。
using System;
using System.Collections.Generic;
static class Example
{
static void Main()
{
BoxEqualityComparer comparer = new();
Dictionary<Box, string> boxes = new(comparer);
AddBox(new Box(4, 3, 4), "red");
AddBox(new Box(4, 3, 4), "blue");
AddBox(new Box(3, 4, 3), "green");
Console.WriteLine($"The dictionary contains {boxes.Count} Box objects.");
void AddBox(Box box, string name)
{
try
{
boxes.Add(box, name);
}
catch (ArgumentException e)
{
Console.WriteLine($"Unable to add {box}: {e.Message}");
}
}
}
}
class Box
{
public int Height { get; }
public int Length { get; }
public int Width { get; }
public Box(int height, int length, int width)
{
Height = height;
Length = length;
Width = width;
}
public override string ToString() => $"({Height}, {Length}, {Width})";
}
class BoxEqualityComparer : IEqualityComparer<Box>
{
public bool Equals(Box? b1, Box? b2)
{
if (ReferenceEquals(b1, b2))
return true;
if (b2 is null || b1 is null)
return false;
return b1.Height == b2.Height
&& b1.Length == b2.Length
&& b1.Width == b2.Width;
}
public int GetHashCode(Box box) => box.Height ^ box.Length ^ box.Width;
}
// 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.
注解
此接口允许实现集合的自定义相等性比较。 也就是说，可以为 类型 T创建自己的相等性定义，并指定此定义与接受泛型接口的 IEqualityComparer<T> 集合类型一起使用。 在.NET Framework，泛型集合类型的构造函数Dictionary<TKey,TValue>接受此接口。
此接口的默认实现由 Default 泛型类的 EqualityComparer<T> 属性提供。 类 StringComparer 实现 IEqualityComparer<T> 类型 String为 。
此接口仅支持相等比较。 用于排序和排序的比较自定义由 IComparer<T> 泛型接口提供。
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 方法测试相等性。 这与 Contains类和其他泛型集合的 Dictionary<TKey,TValue> 、IndexOf、 LastIndexOf和 Remove 方法一致。
方法
| Equals(T, T) |
确定指定的对象是否相等。 |
| GetHashCode(T) |
返回指定对象的哈希代码。 |
