Why are public variables lost after an error? - vba

Question

I have developed the following two subs which create and remove a collection of checkboxes next to a listobject. Each distinct ID in the listobject gets a checkbox. Like this I can approve the listobject entries.
The code is the follwing:
Public CBcollection As Collection
Public CTRLcollection As Collection
Sub create_chbx()
If Approval.CBcollection Is Nothing Then
Dim i As Integer
Dim tbl As ListObject
Dim CTRL As Excel.OLEObject
Dim CB As MSForms.CheckBox
Dim sht As Worksheet
Dim L As Double, T As Double, H As Double, W As Double
Dim rng As Range
Dim ID As Long, oldID As Long
Set CBcollection = New Collection
Set CTRLcollection = New Collection
Set sht = ActiveSheet
Set tbl = sht.ListObjects("ApprovalTBL")
Set rng = tbl.Range(2, 1).Offset(0, -1)
W = 10
H = 10
L = rng.Left + rng.Width / 2 - W / 2
T = rng.Top + rng.Height / 2 - H / 2
For i = 1 To tbl.ListRows.count
ID = tbl.Range(i + 1, 1).Value
If Not (ID = oldID) Then
Set CTRL = sht.OLEObjects.Add(ClassType:="Forms.CheckBox.1", Link:=False, DisplayAsIcon:=False, Left:=L, Top:=T, Width:=W, Height:=H)
Set CB = CTRL.Object
CBcollection.Add Item:=CB
CTRLcollection.Add Item:=CTRL
End If
Set rng = rng.Offset(1, 0)
T = rng.Top + rng.Height / 2 - H / 2
oldID = ID
Next i
End If
End Sub
Sub remove_chbx()
If Not Approval.CBcollection Is Nothing Then
With Approval.CBcollection ' Approval is the module name
While .count > 0
.Remove (.count)
Wend
End With
With Approval.CTRLcollection
While .count > 0
.Item(.count).Delete
.Remove (.count)
Wend
End With
Set Approval.CBcollection = Nothing
Set Approval.CTRLcollection = Nothing
End If
End Sub
This all works pretty well. No double checkboxes and no errors if there are no checkboxes. I am developing an approval scheme were I need to develop and test other modules. If I now run this sub:
Sub IdoStupidStuff()
Dim i As Integer
Dim Im As Image
i = 1
Set Im = i
End Sub
It will give me an error. If I then try to run one of my checkbox subs they will not work properly anymore. The collection is deleted by the error and I am no longer able to access the collections. Why does this happen and am I able to counter act this other then just not causing errors? Is there a better way to implement such a system were loss of collections is not an issue?

Answer 1

You could wrap the Collection object in a Property and let it handle the object creation:
Private mCollection As Collection
Public Property Get TheCollection() As Collection
If mCollection Is Nothing Then Set mCollection = New Collection
Set TheCollection = mCollection
End Property
To call it:
TheCollection.Count

Answer 2

Try On Error Resume Next before the line that causes the error. It will skip the problem and your vairables will still be available.
However this will not solve your error. Try to make a seperate hidden sheet in your workbook to store your global variables so they won't go missing.
f.ex.:
Private Sub CreateSheet()
Dim ws As Worksheet
With ThisWorkbook
Set ws = .Sheets.Add(After:=.Sheets(.Sheets.Count))
ws.Name = "Global"
.Worksheets("Global").Visible = False
End With
End Sub