Events propagation

[thegios]

I have a CWorkflow class, containing a Cenclosures class, which is a collection class of CEnclosure items.

CEnclosure fires a GotDirty event when an enclosure's property is changed.
Cenclosures catches the CEnclosure.GotDirty event and fires another GotDirty event; it fires a GotDirty event

even when a new enclosure is added or an existing one is deleted.
Cworkflow catches the CEnclosures.GotDirty event and fires another GotDirty event; it fires a GotDirty event

even when a workflow's property is cahnged.
My main form catches the CWorkflow.GotDirty event and displays a message box.

This menas that in the form, if I create a workflow object, I change one of its property, then I add an

enclosure and I change one of the enclosure's property, 4 message boxes should appear: one when changing the

workflow's property; two when adding an enclosure (because I create a new enclosure and set its property and

ebcause the collection class is changed) and one when changing a property of the just added enclosure.

The problem is hat I get only 3 message boxes, because the last one is missing, that is no event if fired/caught

when changing a property of the just added enclosure.

Code follows...

------------------------------------------------------
'CEnclosure
------------------------------------------------------

Option Explicit

Public Event GotDirty()

Private mReference As String
Public Property Let Reference(Value As String)
    mReference = Value
    RaiseEvent GotDirty
End Property
Public Property Get Reference() As String
    Reference = mReference
End Property

Private Sub Class_Initialize()
    mReference = ""
End Sub

------------------------------------------------------
'CEnclosures
------------------------------------------------------

Option Explicit

Implements IUnknown

Public Event GotDirty()

Private mCol As Collection

Private WithEvents newENC As CEnclosure

Public Property Get NewEnum() As IUnknown
    Set NewEnum = mCol.[_NewEnum]
End Property

Public Property Get Item(IndexKey As Variant) As CEnclosure
    Set Item = mCol(IndexKey)
End Property

Public Property Get Count() As Long
    Count = mCol.Count
End Property

Public Sub Remove(IndexKey As Variant)
    mCol.Remove IndexKey
    
    RaiseEvent GotDirty
End Sub

Public Function Add(Index As Integer, Reference As String) As CEnclosure
    Set newENC = New CEnclosure
    
    newENC.Reference = Reference
    
    If mCol.Count = 0 Then
        mCol.Add newENC
    ElseIf Index > mCol.Count Then
        mCol.Add newENC, , , mCol.Count
    Else
        mCol.Add newENC, , Index
    End If
    
    RaiseEvent GotDirty
        
    Set Add = newENC
    Set newENC = Nothing
End Function

Private Sub Class_Initialize()
    Set mCol = New Collection
End Sub

Private Sub Class_Terminate()
    Set mCol = Nothing
End Sub

Private Sub newENC_GotDirty()
    RaiseEvent GotDirty
End Sub

------------------------------------------------------
'CWorkflow
------------------------------------------------------

Option Explicit

Public Event GotDirty()

Private WithEvents mENC As CEnclosures

Private mInfo As String

Public Property Let Info(Value As String)
    mInfo = Value
    RaiseEvent GotDirty
End Property
Public Property Get Info() As String
    Info = mInfo
End Property

Public Property Get Enclosures() As CEnclosures
    Set Enclosures = mENC
End Property

Private Sub Class_Initialize()
    mInfo = ""
    
    Set mENC = New CEnclosures
End Sub

Private Sub Class_Terminate()
    Set mENC = Nothing
End Sub

Private Sub mENC_GotDirty()
    RaiseEvent GotDirty
End Sub

------------------------------------------------------
'FORM
------------------------------------------------------

Option Explicit

Dim WithEvents w As CWorkflow

Private Sub Command1_Click()
    Dim el As CEnclosures
    Dim e As CEnclosure
    
    Set w = New CWorkflow
    w.Info = "Info" 'Here 1 message box is displayed since one event is fired from CWorkflow
    
    Set el = w.Enclosures
    Set e = el.Add(3, "Enclosur") 'Here 2 message boxes are displayed
                                  'since 2 events are fired: one from CEnclosure and
                                  'one from CEnclosures
    
    e.Reference = "Enclosure" 'Here 1 message box should be displayed but it is not
                              'because no event is fired
End Sub

Private Sub w_GotDirty()
    MsgBox "GotDirty"
End Sub

[mstraf]

I believe this is what is happening.

In CEnclosures, you declare a CEnclosure with events, and you add it to the collection. But then you set it to nothing, so at this points the object still exists because it is still referenced by the Collection, but has lost the Sync interface that allows the event to be fired.

In situations like this (it is the same in an array of objects, not only a Collection) one solution is to add an extra class that raises the event, and pass it around:

CEventSync code:

Public event MyEvent()
public sub RaiseMyEvent()
raiseevent MyEvent
end sub

Create one instance withevents of this class in CEnclosures:

private withevents m_c as CEventSync
private sub m_c_MyEvent()
raiseevent GotDirty
end sub

and pass this class to each of the created CEnclosure objects. In CEnclosure, keep a reference of this class in a private variable then, instead of raising the event, call the RaiseMyEvent method of this new class.

This is just one method, and it is the one I prefer because it does not create any circular reference and does not need any global object.

Hope this is clear, please let me know
Marco