three-valued-property-changed.vb

Imports System.ComponentModel

Class BindableRange
    Implements INotifyPropertyChanged

    Private _EndDate As Date?

    Property EndDate As Date?
        Get
            Return _EndDate
        End Get
        Set(value As Date?)
            ' This line here:
            If value = _EndDate Then Return

            _EndDate = value

            RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(NameOf(EndDate)))
        End Set
    End Property

    Public Event PropertyChanged As PropertyChangedEventHandler _
        Implements INotifyPropertyChanged.PropertyChanged

End Class

Module Program

    WithEvents Range As New BindableRange

    Sub Main()

        Range.EndDate = Today
        Range.EndDate = Today
        Range.EndDate = Nothing
        Range.EndDate = Nothing

    End Sub

    Private Sub BindableRange_PropertyChanged(sender As Object, e As PropertyChangedEventArgs) _
        Handles Range.PropertyChanged

        Console.WriteLine(e.PropertyName & " changed.")
    End Sub

End Module