Class (Static) Methods in VBA

Question

I wonder, whether it is possible to create class-methods in VBA. By class-method I mean methods that can be called without having an object of the class. The 'static'-keyword does that trick in C++ and Java.

In the example below, I try to create a static factory method.

Example:

'Classmodule Person' Option Explicit Private m_name As String Public Property Let name(name As String)     m_name = name End Property Public Function sayHello() As String     Debug.Print "Hi, I am " & m_name & "!" End Function  '---How to make the following method static?---' Public Function Create(name As String) As Person     Dim p As New Person     p.m_name = name     Set Create = p End Function  'Using Person' Dim p As New Person p.name = "Bob" p.sayHello 'Works as expected' Set p2 = Person.Create("Bob") 'Yields an error' 

Answer 1

1. Create a normal class containing the public method(s) you need to be 'static'

2. Include a public method [in this 'static' class] that initialises the [private] 'static fields' within the class (it can take parameters if you wish)

3. Create a module acts as a factory

Public Function CreateStaticClass(parameters for 'constructor') As StaticClass      Dim static As StaticClass     Set static = New StaticClass     Call StaticClass.Constructor(pass in parameters)     Set CreateStaticClass = static  End Function 

4. you can now use the 'static' class by calling CreateStaticClass('parameters').MethodName('parameters') there is no need to initialise the instance as that is done by the factory method

5. (Optional) If you want to enforce singleton instances you can create a module that acts as a singleton container - include a private instance variable and a public accessor property. optionally you can use a 'let' setter to allow the singleton to be 'replaced' with a new [static] class (using different constructor parameters - see #2,3). Use 'Let' for the setter, so you can assign the singleton without using 'set' ala OO languages

Private curStaticClass as StaticClass  Public Property Get CurrentStaticClass() As StaticClass       If curStaticClass Is Nothing Then Set curStaticClass = CreateStaticClass      Set CurrentStaticClass = curStaticClass    End Property  Public Property Let CurrentStaticClass(value As StaticClass)      If Not (curStaticClass Is Nothing) Then Set curStaticClass = Nothing      Set curStaticClass = value   End Property 

6. To assign the singleton:

CurrentStaticClass = CreateStaticClass(parameters) 

7. To use the singleton:

[value = ] CurrentStaticClass.MethodName(parameters)