VBA linking Class(es) and Userforms

[saboh12617]

Hello,

I am a long time user of VBA but i never had the need to deal with userforms until recently i started digging into it.
I have been following OOP lessons at university and as a rubberduck user (in the sense that i read a lot of the VBA advices given on the blog) i found more coherent the idea to have the "running code" in procedures outside of the userform object, which end up being a "caller/receiver".

However i am struggling on the implementation as there is very few documentation on the latter.

I am aware that in a real project i would do a Class-based model, and then call its procedures via the userform events.

But i was trying to wrap the userform in another class, as one of its property, and then for example implement a display function which would allow me to display different instances of the same userform "frame".
I tried a simple example as given below but it wont work as i can not create two instances of the same userform at the same time. Is it normal?

' Class1.cls
Option Explicit

Private Type tUF
  instanceUF As UserForm1
End Type

Private this As tUF

Private Sub Class_Initialize()
  Set this.instanceUF = UserForm1
End Sub

Public Sub display()
  this.instanceUF.Show
End Sub

Sub testuf()
  Dim uf1 As Class1
  Dim uf2 As Class1
 
  Set uf1 = New Class1
  Set uf2 = New Class1
 
  uf1.display
  uf2.display   ' error, userform object does no longer exist
End Sub

The UserForm1 is an empty UserForm with no Sub.

If i assign the value after closing the first instance, then it works.

Sub testuf()
  Dim uf1 As Class1
  Dim uf2 As Class1
 
  Set uf1 = New Class1
  
 
  uf1.display
  Set uf2 = New Class1
  uf2.display   ' no error
End Sub

However if i assign it before, then i suppose both my classes "instanceUF" are pointers to the same object.
Is there a turnaround possible? Should i implement a function "on close [X]" to handle it correctly? how to do so?

Thank you for your answers

 

[saboh12617]

I forgot, here is the error raised

 

[Jaafar Tribak]

However if i assign it before, then i suppose both my classes "instanceUF" are pointers to the same object.

Yes. That's what you are doing in the Class_Initialize event.

To have a diff UserFrom instance for each class instance, create a new userform as follows:

Private Sub Class_Initialize()
  Set this.instanceUF = New UserForm1
End Sub

 

[saboh12617]

Oh...
Indeed it makes sense, what doesn't make sense is that i did not need to put "New" in the first place. But i guess it has to do with the "Auto instantiation" of the Userforms. They are a bit confusing at the beginning due to those, i guess, "user friendly" features that automatically do things and by doing so do not raise errors or alerts...

Thanks for your time, it works.

 

[Jaafar Tribak]

But i guess it has to do with the "Auto instantiation" of the Userforms.

Yes. This can be confusing. As you said, this is due to the UserForms Instancing VB_PredeclaredId attribute value being set to True by default. However, subsequent instances can't be created without the New keyword unless the previous default instance is destroyed.