Create and loop through collection subset of controls - vb.net

Question

Im making a small vb.net windows form application in which I have 4 ComboBoxes. I would like to add the ComboBoxes to a collection and be able to loop through that collection to refer to each one.
There are other ComboBoxes on the form so I cannot just use the collection for the entire form (the form layout cannot be changed, e.g. to add a container, etc).
I was thinking something like the following:
Public Class Form1
Dim IoTypeCombos As New ControlCollection(Me) From {Me.IO1_ComboBox, Me.IO2_ComboBox, Me.IO3_ComboBox, Me.IO4_ComboBox}
Dim IoTypes As New Collection() From {"Out 0", "Out 1", "Input", "Analog"}
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
For Each cb As combobox In Me.IoTypeCombos
FillComboBox(cb, Types)
Next
End Sub
Function FillComboBox(cb As Control, cc As Collection) As Boolean
Dim cbc As ComboBox = CType(cb, ComboBox)
If cc.Count = 0 Then
Return False
End If
For Each cn In cc
cbc.Items.Add(cn)
Next
Return True
End Function
This doesn't raise any exception, BUT it doesn't populate the ComboBoxes either :(
The FillComboBox() works perfectly if I pass a single control to it.
What am I doing wrong? Thanks

Answer 1

This line is illegal:
Public Class Form1
Dim IoTypeCombos As New ControlCollection(Me) From {Me.IO1_ComboBox,
Me.IO2_ComboBox, Me.IO3_ComboBox, Me.IO4_ComboBox }
That code will run before the constructor, before Me or ION_ComboBox exist. In this case, the resulting collection contains nothing since there is nothing to put in it yet.
In other cases, referencing controls before they exist can result in a NullReference being thrown, but due to an odd bug it may not be reported. When that happens, the rest of the code is skipped and the form simply shown.
In either case, the solution is to declare your collection at the form level, but populate it in the form load event once the controls do exist. I would also use a Collection(Of T) instead (an array or List(Of T) will also work, the OP uses/asks about a collection though):
Imports System.Collections.ObjectModel
Public Class Form1
Dim IoTypeCombos As Collection(Of ComboBox) ' form and controls Do No Exist yet
Public Sub New
'...
InitializeComponent()
' NOW they exist
End Sub
Sub Form_Load
IoTypeCombos = New Collection(Of ComboBox)
IoTypeCombos.Add(IO1_ComboBox)
IoTypeCombos.Add(IO2_ComboBox)
...
If you use a List(Of ComboBox), you can populate it different ways:
' in the ctor:
IoTypeCombos = New List(Of ComboBox)({IO1_ComboBox, IO2_ComboBox...})
' using AddRange:
IoTypeCombos.AddRange({IO1_ComboBox, IO2_ComboBox...})

Answer 2

Not sure if you need the where clause, but if you have other comboboxes that do not have names like this and do not want them in the collection then you do need it.
Dim IoTypeComboboxes =
Me.Controls.OfType(Of Combobox)().Where(Function(cb) cb.Name.StartsWith("IO")).ToList()

Answer 3

'on yourFormName
'added :
'45 PictureBox:("PicBarNum1_NotLastOdig" to "PicBarNum45_NotLastOdig")
'added:
'45 PictureBox:("PicBarNum1_UkOdig" to "PicBarNum45_UkOdig")
Public Class yourFormName
Private picbarlistNum1to45_UkOdig As New List(Of PictureBox)
Private picbarlistNum1to45_UkLastNotOdig As New List(Of PictureBox)
Private sub yourFormName_Load
Call AddPicBoxesInList_OdigNoOdig()
End sub
Private Sub AddPicBoxesInList_OdigNoOdig()
picbarlistNum1to45_UkOdig.Clear()
picbarlistNum1to45_UkLastNotOdig.Clear()
picbarlistNum1to45_UkOdig = Me.Controls(0).Controls.OfType(Of PictureBox)()
.Where(Function(pb) pb.Name.StartsWith("PicBarNum") And
pb.Name.EndsWith("_UkOdig")).ToList()
picbarlistNum1to45_UkLastNotOdig = Me.Controls(0).Controls.OfType(Of
PictureBox)().Where(Function(pb) pb.Name.StartsWith("PicBarNum") And
pb.Name.EndsWith("_NotLastOdig")).ToList()
End Sub
End Class