Split Form creates a separate collections for each of its parts - vba

Question

I have a split Form in MS Access where users can select records in the datasheet and add it to a listbox in the Form thereby creating custom selection of records.
The procedure is based on a collection. A selected record gets transformed into a custom Object which gets added to the collection which in turn is used to populate the listbox. I have buttons to Add a Record, Remove a Record or Clear All which work fine.
However I thought, that pressing all these buttons is a bit tedious if you create a Selection of more then a dozen records, so i reckoned it should be simple to bind the actions of the Add and Remove buttons to the doubleclick event of a datasheet field and the listbox respectively.
Unfortunately i was mistaken as this broke the form. While a doubleclick on a field in the datasheet part of the form added the record to the listbox it was now unable to remove an item from the underlying collection giving me Run-time error 5: "Invalid procedure call or argument". Furthermore the clear all Button doesn't properly reset the collection anymore. When trying to Clear and adding a record of the previous selection the code returns my custom error that the record is already part of the selection and the listbox gets populated with the whole previous selection, which should be deleted. This leaves me to believe, that for some Reason the collection gets duplicated or something along these lines. Any hints into the underlying problem is apprecciated. Code as Follows:
Option Compare Database
Dim PersColl As New Collection
Private Sub AddPerson_Click()
AddPersToColl Me!ID
FillListbox
End Sub
Private Sub btnClear_Click()
Set PersColl = Nothing
lBoxSelection.RowSource = vbaNullString
End Sub
Private Sub btnRemovePers_Click()
PersColl.Remove CStr(lBoxSelection.Value)
FillListbox
End Sub
Private Sub FillListbox()
Dim Pers As Person
lBoxSelection.RowSource = vbaNullString
For Each Pers In PersColl
lBoxSelection.AddItem Pers.ID & ";" & Pers.FullName
Next Pers
lBoxSelection.Requery
End Sub
Private Function HasKey(coll As Collection, strKey As String) As Boolean
Dim var As Variant
On Error Resume Next
var = IsObject(coll(strKey))
HasKey = Not IsEmpty(var)
Err.Clear
End Function
Private Sub AddPersToColl(PersonId As Long)
Dim Pers As Person
Set Pers = New Person
Pers.ID = PersonId
If HasKey(PersColl, CStr(PersonId)) = False Then
PersColl.Add Item:=Pers, Key:=CStr(PersonId)
Else: MsgBox "Person Bereits ausgewählt"
End If
End Sub
This works alone, but Simply Adding this breaks it as described above.
Private Sub Nachname_DblClick(Cancel As Integer)
AddPersToColl Me!ID
FillListbox
End Sub
Further testing showed that its not working if i simply remove the Private Sub AddPerson_Click()
Edit1:
Clarification: I suspected that having 2 different events calling the same subs would somehow duplicate the collection in memory, therefore removing one event should work. This is however not the case. Having the subs called by a button_Click event works fine but having the same subs called by a double_click event prompts the behaviour described above. The issue seems therefore not in having the subs bound to more than one event, but rather by having them bound to the Double_Click event.
Edit2: I located the issue but I Haven't found a solution yet. Looks like Split-Forms are not really connected when it comes to the underlying vba code. DoubleClicking on the record in the datasheet view creates a Collection while using the buttons on the form part creates another one. When trying to remove a collection item by clicking a button on the form, it prompts an error because this collection is empty. However clicking the clear all button on the form part doesn't clear the collection associated with the datasheet part.
Putting the collection outside into a separate module might be a workaround but i would appreciate any suggestions which would let me keep the Code in the form module.

Answer 1

The behavior is caused by the split form which creates two separate collections for each one of its parts. Depending from where the event which manipulates the collection gets fired one or the other is affected. I suspect that the split form is in essence not a single form, but rather 2 instances of the same form-class.
A Solution is to Declare a collection in a separate module "Coll":
Option Compare Database
Dim mColl as new Collection
Public Function GetColl() as Collection
Set GetColl= mColl
End Function
And then remove the Declaration of the Collection in the SplitFormclass and Declare the Collection in every Function or Sub by referencing the collection in the separate Module like in the following example:
Option Compare Database
Private Sub AddPersToColl(PersonId As Long)
Dim Pers As Person
Dim PersColl as Collection
Set PersColl = Coll.GetColl
Set Pers = New Person
Pers.ID = PersonId
If HasKey(PersColl, CStr(PersonId)) = False Then
PersColl.Add Item:=Pers, Key:=CStr(PersonId)
Else: MsgBox "Person Bereits ausgewählt"
End If
End Sub
This forces the form to use the same Collection regardless if the event is fired from the form or datasheet part of the split-form. Any Further information is appreciated but the matter is solved for now.
Thanks everyone for their time