Subclass/Superclass - If a subclass is cast as its superclass, is there a way to use the overloaded properties of the subclass? - vb.net

Question

Sorry if the title isn't very clear. This is a VB.NET (2010) question
I have a superclass called "Device" which has a number of subclasses that inherit it. Some of those subclasses also have subclasses. In particular, I have a class called "TwinCatIntegerDevice" which inherits "TwinCatDevice" which inherits "Device."
The relevant parts of Device look like this:
Public Class Device
Private _Setpoints As New List(Of Double)
Public Overridable Property Setpoints As List(Of Double)
Get
Return _Setpoints
End Get
Set(ByVal value As List(Of Double))
_Setpoints = value
_SetpointsTb.Clear()
For Each setpoint In value
Dim setpointTb As New TextBox
setpointTb.Text = setpoint.ToString
_SetpointsTb.Add(setpointTb)
Next
End Set
End Property
Private _SetpointsTb As New List(Of TextBox)
Public Overridable Property SetpointsTb As List(Of TextBox)
Get
Return _SetpointsTb
End Get
Set(ByVal value As List(Of TextBox))
_SetpointsTb = value
Me._Setpoints.Clear()
For Each setpoint In value
Me._Setpoints.Add(setpoint.Text)
Next
End Set
End Property
End Class
The TwinCatDevice class does not overload Setpoints or SetpointsTb.
The TwinCatIntegerDevice class does:
Public Class TwinCatIntegerDevice
Inherits TwinCatDevice
Private _Setpoints As New List(Of Integer)
Public Overloads Property Setpoints As List(Of Integer)
Get
Return _Setpoints
End Get
Set(ByVal value As List(Of Integer))
_Setpoints = value
_SetpointsTb.Clear()
For Each setpoint In value
Dim setpointTb As New TextBox
setpointTb.Text = setpoint.ToString
_SetpointsTb.Add(setpointTb)
Next
End Set
End Property
Private _SetpointsTb As New List(Of TextBox)
Public Overloads Property SetpointsTb As List(Of TextBox)
Get
Return _SetpointsTb
End Get
Set(ByVal value As List(Of TextBox))
_SetpointsTb = value
Me._Setpoints.Clear()
For Each setpoint In value
Me._Setpoints.Add(setpoint.Text)
Next
End Set
End Property
End Class
Now, the problem. I try to set the setpoints using a subroutine like so:
Private Sub FetchDeviceRecipe(ByRef device As Device, ByRef excelSheet As ExcelWorksheet, ByVal row As Integer)
Dim lastCol As Integer = NumberOfProcessSteps + 1
Try
For col = 2 To lastCol
Dim setpoint As New TextBox
setpoint.Text = excelSheet.Cells(row, col).Value
device.SetpointsTb.Add(setpoint)
Next
device.SetpointsTb = device.SetpointsTb
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
(I know that is terrible code :X, I'm a beginner)
Crucially, I'm passing the device as the Device superclass (so that I don't have to have a separate subroutine for each sub-type).
When I do this for a TwinCatIntegerDevice called "ThisDevice" after it has been passed to the subroutine:
MsgBox("As Device: " & CType(ThisDevice, Device).Setpoints.Count.ToString & vbNewLine & _
"As TwinCatDevice: " & CType(ThisDevice, TwinCatDevice).Setpoints.Count.ToString & vbNewLine & _
"As TwinCatIntegerDevice: " & CType(ThisDevice, TwinCatIntegerDevice).Setpoints.Count.ToString)
I get the following (9 is the correct number of setpoints in this case):
As Device: 9
As TwinCatDevice: 9
As TwinCatIntegerDevice: 0
Does anyone know why the TwinCatInteger device class apparently has a different variable for Setpoints when it is cast as its superclass Device?
I'm sorry if this seems a bit incoherent. Any help would be great! Even regarding form or anything else. I'm still trying to figure this whole VB.NET thing out.

Answer 1

I think what you want to do, is remove your "OverLoads" keyword on the "TwinCatIntegerDevice" class, and replace it with the keyword "Shadows".