LINQ 区别不工作

Question

我正在尝试 select 与我的 class 不同的实例，但它不起作用，即使在实施 IEqualityComparer（如此处所述：https://msdn.microsoft.com/en-us/library/bb338049.aspx）和 IEquatable[=13= 之后也是如此]

有人可以帮忙吗？

Public Class Teste
  Implements IEquatable(Of Teste), IEqualityComparer(Of Teste)
  Private _Codigo As Integer
  Public Property Codigo() As Integer
    Get
      Return _Codigo
    End Get
    Set(ByVal value As Integer)
      _Codigo = value
    End Set
  End Property
  Public Sub New(id As Integer)
    Me.Codigo = id
  End Sub

  Public Overrides Function Equals(obj As Object) As Boolean
    Return DirectCast(obj, Teste).Codigo = Me.Codigo
  End Function

  Public Function Equals1(other As Teste) As Boolean Implements IEquatable(Of Teste).Equals
    Return Me.Codigo = other.Codigo
  End Function

  Public Function Equals2(x As Teste, y As Teste) As Boolean Implements IEqualityComparer(Of Teste).Equals
    Return x.Codigo = y.Codigo
  End Function

  Public Function GetHashCode1(obj As Teste) As Integer Implements IEqualityComparer(Of Teste).GetHashCode
    Return DirectCast(obj, Teste).Codigo
  End Function
End Class

测试：

Dim p1 As New Teste(78)
Dim p2 As New Teste(78)
Dim l As New List(Of Teste) From {p1, p2}
MsgBox(l.Count())
MsgBox(l.Distinct().Count())

我有两个消息框都显示“2”。

Answer 1

您需要告诉 Distinct 方法使用什么相等比较器。我也会把它拆分成它自己的 class。例如：

Public Class TesteEqualityComparer 
    Implements IEqualityComparer(Of Teste)

    Public Function Equals2(x As Teste, y As Teste) As Boolean Implements IEqualityComparer(Of Teste).Equals
        Return x.Codigo = y.Codigo
    End Function

    Public Function GetHashCode1(obj As Teste) As Integer Implements IEqualityComparer(Of Teste).GetHashCode
        Return obj.Codigo.GetHashCode()
    End Function
End Class

现在您的查询是：

MsgBox(l.Distinct(New TesteEqualityComparer()).Count())

LINQ 区别不工作

LINQ Distinct Not Working

linq

vb.net

distinct

iequatable

iequalitycomparer