VBA - Trying to understand how to call Class Modules - excel

Question

I'm learning VBA through Google, YouTube, etc.. and I came across Class Modules.
I have a Tracker Template.
Every few days I get a report sent to me ("Ice cream FG Inv.xlsm")
While trying to understand Class Modules, I found a template that created a Class Module (within the Tracker Template) WBIceCreamFGINVxlsm creating a CodeName for all of the worksheets within the Ice Cream FG Inv.xlsm Workbook.
Example:
Public Property Get wsinventory() As Worksheet
Set wsinventory = Workbook.Worksheets("Inventory")
End Property
In my module, I want to reference wsinventory, but not understanding exactly how to 'call' the Class Module..
Both Workbooks are Open.
I tried to start with:
Dim Data As Variant
Data = wsinventory.Range("A1").CurrentRegion.Value (**Variable not Defined**)
Then I tried:
Dim wsinventory As Worksheets
With wsinventory
Dim Data As Variant
Data = .Range("A1").CurrentRegion.Value (**Object variable or With variable not set**)
End With
Do I still need to use:
Dim DataSource As Workbook
Set DataSource = Workbooks("Ice Cream FG Inv.xlsm")
With DataSource.Worksheets("Inventory")
End With
If so, what would be the reasoning for using Class Modules?

Answer 1

You need to create a class object before you can access the properties of that class.
Assuming you have this Class and naming it TestClass:
Private pwsinventory As Worksheet
Public Sub init()
Set pwsinventory = Worksheets("Inventory")
End Sub
Public Property Set wsinventory(lwsinventory As Worksheet)
Set pwsinventory = lwsinventory
End Property
Public Property Get wsinventory() As Worksheet
Set wsinventory = pwsinventory
End Property
You can set / get the properties like so:
Sub test()
Dim datacls As TestClass
Dim data As Worksheet
Set datacls = New TestClass
Set datacls.wsinventory = Worksheets("inventory")
Set data = datacls.wsinventory
Debug.Print data.Name
End Sub
This, however, is kind of weird and when you have a property you don't want to set (you need to pass an argument) you should use an initiate function. Unfortunately there is no way I know of to do this without manually calling that sub after the class object is created.
Sub Test2()
Dim datacls As TestClass
Set datacls = New TestClass
datacls.init
Debug.Print datacls.wsinventory.Name
End Sub
The most common case I use classes for is better containers. Generally storing many of the same class type inside an array / dictionary so it is clear what I'm calling, especially if I need to modify the data in the same manner for each instance.

Answer 2

I am going to give another example. Create a class definition and name it ArrayData, and define multiple initialization subroutines
ArrayData.cls
Private m_data() As Variant
Private Sub Class_Initialize()
End Sub
Public Sub IntializeEmpty(ByVal rows As Long, ByVal columns As Long)
ReDim m_data(1 To count, 1 To columns)
End Sub
Public Sub InitializeFromRange(ByRef target As Range)
If target.rows.count > 1 Or target.columns.count > 1 Then
m_data = target.Value2
Else
ReDim m_data(1 To 1, 1 To 1)
m_data(1, 1) = target.Value
End If
End Sub
Public Sub InitializeFromArray(ByRef data() As Variant)
m_data = data
End Sub
Public Property Get RowCount() As Long
RowCount = UBound(m_data, 1) - LBound(m_data, 1) + 1
End Property
Public Property Get ColCount() As Long
ColCount = UBound(m_data, 2) - LBound(m_data, 2) + 1
End Property
Public Property Get Item(ByVal row As Long, ByVal col As Long) As Variant
Item = m_data(row, col)
End Property
Public Property Let Item(ByVal row As Long, ByVal col As Long, ByVal x As Variant)
m_data(row, col) = x
End Property
Module
To test the code in a code module initialize the class with the New keyword and then call one of the custom initialization subroutines.
Public Sub TestArray()
Dim arr As New ArrayData
arr.InitializeFromRange Sheet1.Range("A2").Resize(10, 1)
Dim i As Long
For i = 1 To arr.RowCount
Debug.Print arr.Item(i, 1)
Next i
End Sub
PS. Also read this article on how to designate one property as the default. In the example above if Item was the default property then you could write code such as
Debug.Print arr(5,2)
instead of
Debug.Pring arr.Item(5,2)