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excel – Modify an existing VBA class

Posted by: admin April 23, 2020 Leave a comment

Questions:

I would like to know if there is some way to add your own methods/properties to an existing VBA class (such Range, Charts, etc).

An example:
I would like the currently VBA class Worksheet have a specific method done by myself, something like:

'Worksheet methods
Public Sub LookFor (ByVal Value as String)
    'My code
End Sub

Then I can call from any declared Worksheet class this function.

In class MyClass:

'MyClass members
Private pWS1 as Worksheet
Private pWS2 as Worksheet
Private pWS3 as Worksheet


'MyClass methods
Private Sub Class_Initialization()
    Set pWS1 = Worksheets("WS1")
    Set pWS2 = Worksheets("WS2")
    Set pWS3 = Worksheets("WS3")
End Sub

Public Sub Example()
    pWS1.LookFor("abc")
    pWS2.LookFor("123")
    pWS3.LookFor("def")
End Sub    

Thanks!

How to&Answers:

There is no direct way to do this in VBA.

Best you can do is create a “wrapper” class which has a private Worksheet member, and expose that via a Sheet property. Add your “extension” methods to the class and have them operate on m_sheet.

Initialize your class by creating an instance of it and assigning a worksheet object to its Sheet property.

You can call your “extension” methods directly on the object, and any existing methods you’d access via the Sheet property.

Class MySheet:

Private m_sht As Worksheet


Public Property Set Sheet(ws As Worksheet)
    Set m_sht = ws
End Property

Public Property Get Sheet() As Worksheet
    Set Sheet = m_sht
End Property

Public Property Get CountHellos() As Long
    CountHellos = Application.CountIf(m_sht.Cells, "Hello")
End Property

Test sub:

Sub Tester()

    Dim sht As MySheet

    Set sht = New MySheet

    Set sht.Sheet = ActiveSheet

    MsgBox sht.CountHellos '<< "extension" method

    MsgBox sht.Sheet.Rows.Count '<< built-in object property

End Sub

Edit: you might be able to make the Sheet property the default for your class by following the steps outlined by Chip here: http://www.cpearson.com/excel/DefaultMember.aspx

May work to allow you to skip the Sheet property when working with instances of your class (but I’ve not tested this)

Answer:

What you are looking for is called “Extension” methods in tradition Object Oriented Programming Languages.

See MSDN: Extension Methods (Visual Basic)

AFAIK, what you are looking for is not supported / available in traditional Visual Basic for Applications (VBA).

Here’s an example of doing extension methods in Visual Basic .Net (VB.Net) from the MSDN source.

Step 1. Declare Extension method like so…

enter image description here

Step 2. Call extension method like so…

enter image description here