How to add an object to a collection?

[sueb]

I have a collection manager (managing instances of forms) that was working fine, but I broke it and, since it was developed by someone else, I don't understand it well, so I don't know how to fix it.

The problem is that when I try to open another instance of a form, I get the runtime error 457, saying "This key is already associated with an element of this collection" on line 27 of the following code:

Function OpenAClient(frmForm As Form, _
                     frmCaption As String, _
                     frmCollection As Collection, _
                     Optional strFilter As String = "")
    ' Purpose: Open a new instance of the specified form, manage its properties, and append it
    ' to the specified collection
 
    ' Open a new instance and set a caption
    frmForm.Caption = frmCaption & " " & frmCollection.Count & ", opened " & Now()
 
    ' Set the form's editing mode according to the current user's privileges
    If ReadWrite Then
        frmForm.RecordsetType = conDynaset
    Else
        frmForm.RecordsetType = conSnapshot
    End If
 
    ' Use a pointer, if one was supplied
    If strFilter & "" <> "" Then
        frmForm.Filter = strFilter
        frmForm.FilterOn = True
    Else
        frmForm.FilterOn = False
    End If
 
    ' Append it to the specified collection and display it
    frmCollection.Add Item:=frmForm, Key:=CStr(frmForm.Hwnd)
    frmForm.Visible = True
 
End Function
 

I originally had just one collection of forms, but later needed this same functionality for other forms, so I made it a common routine that accepts the collection to handle (instead of hard-coding the collection within it). That's what broke it, I think. I suspect that the property .Hwnd (what does that stand for, anyway?) is not getting incremented; in fact, I suspect that the collection is not getting returned out of this function. I don't know how to specify an "in out" parameter, but I'm thinking that's what needs to happen?

Here's an example of how I call it:

Function OpenAnOverviewClient(Optional strFilter As String = "")
    OpenAClient Form_Patient_IUR_Overview, "PAT", clnOverviewClient, strFilter
End Function
 

[NeoPa]

Another question of quite enormous scope again I'm afraid Sue.

What I can tell you is that to pass a parameter to a procedure which can be used by the procedure as well as updated (such that the calling code has the updated state of the parameter when it's finished) you use the ByRef keyword. Here's an illustration :

Private Sub TestByRef(ByRef intX As Integer)
    intX = intX + 10
End Sub

The following code illustrates this working :

Dim intA As Integer
 
intA = 25
Call TestByRef(intA)
Debug.Print intA

The value printed in the Immediate Pane would be 35. Not 25 as you would expect without ByRef being specified.

[sueb]

I added "ByRef" to the parameter frmCollection, but still got the same error. What is happening with that .Hwnd property anyway? What is it?

[ADezii]

The problem is that your Function never actually creates a New Instance of the Form passed to it as an Argument. This is only accomplished by using the New Keyword, as in:

Dim frm As Form_frmCustomers
Set frm = New Form_frmCustomers
 
'Assuming your Collection has already been Defined
frmForm.Caption = "Instance Number " & (frmCollection.Count + 1) & ", opened " & Now()
 
' Append it to the specified collection and display it
frmCollection.Add Item:=frm, Key:=CStr(frm.hWnd)
frmForm.Visible = True

P.S. - The hWnd Property of a Form is a Unique Long Integer Value, assigned by Microsoft Windows to the Current Window (in this case each Form Instance). Since the 'Key' Component of a Collection must be a Unique Value for each Element, hWnd is a Logical choice.

[sueb]

But how do I pass in to the function the different forms that I want it to manage? I have four different form collections that I want to manage in the same way, without having to duplicate code. In the example, the Dim statement is serving a single form type.

[ADezii]

@sueb, I'm really pressed for time, but I threw together something for you to look at, that should be workable.

[sueb]

@ADezii, thanks a bunch--I'll look at it as soon as I get a chance!

[sueb]

@ADezii, this looks like it may have done the trick! So, basically, the change is to add, to each calling routine, a Dim and a Set statement to create the object that I'm sending in to the collection manager.

Thanks--I hadn't really understood the scope of the object correctly, but this makes it clearer.

[sueb]

@NeoPa, thanks for the explanation of the meaning and use of the .Hwnd property--that helps my basic understanding of the objects being managed.

[NeoPa]

I'm glad things seem to be sorted out now.

I think my point was about the ByRef actually, but that's just being precise ;-)

I think you've already got what you need from ADezii, but collections can be managed within a procedure if one of the arguments to the procedure is a collection object. In such cases the ByRef effect is automatic anyway of course.