[AccessD] Global default class instance

[Ryan W]

Mike Wolfe has a ton of great class articles on hidden properties and
fantastic uses over on https://www.nolongerset.com

He even shares code on how to export a class, insert the text you mentioned
and re-import it all programmatically:
https://nolongerset.com/setpredeclaredid/



On Fri, Oct 28, 2022 at 3:43 AM John Colby <jwcolby at gmail.com> wrote:

> I learned something today.  Microsoft Access (VBA) has the ability to have
> a default class instance.  What this means is that you do not have to
> instantiate the class to use it
>
> Under normal circumstances, in order to use a class you have to dimension a
> variable to hold a class and then instantiate the class in order to use
> it.  A 'default class instance' means that Access creates an instance of
> the class for you without going through all this.
>
>
> As you may know, a class has hidden attributes.
>
>
>    -
>
>    In the menu bar, click create, then in the toolbar click Class Module
>    -
>
>    A class module will be created named Class1. Save that.
>    -
>
>    Open the Class1 in the editor
>    -
>
>    Click File / Export file
>    -
>
>    Navigate to the location where your database container is stored.
>    -
>
>    Click Save. A file with the name of the module and a .cls extension will
>    be created, in this case ‘Class1.cls’
>    -
>
>    Open that file in notepad.
>
>
> At the top of the file you will see a header that looks similar to this:
>
>
> VERSION 1.0 CLASS
>
> BEGIN
>
> MultiUse = -1 'True
>
> END
>
> Attribute VB_Name = “Class1”
>
> Attribute VB_GlobalNameSpace = False
>
> Attribute VB_Creatable = False
>
> Attribute VB_PredeclaredId = False
>
> Attribute VB_Exposed = False
>
> Option Compare Database
>
> Option Explicit
>
> These attributes can be edited.  Edit the VB_PredeclaredID = True.
> Save the file.
> In the VBA editor, click File, Import File.  Select the file you just
> edited and click Open
>
> Add the following code to the class.
>
> Public Function GiveMeATwo() As Integer
>     GiveMeATwo = 2
> End Function
>
> Save the class.
>
> In the immediate window type
>
> Debug.Print Class1.GiveMeATwo
>
> And hit enter.
>
> The method of the class should execute and you should see a 2 on the next
> line.  Notice we never instantiated Class1.
>
> In my testing however, the Class_Initialize() sub never fires, so if you
> use that to initialize things (my framework 'initializes' using that event
> sink) then you need to either go ahead and use the dimension method or call
> an Init() method of your own to perform this initialization.
>
> At any rate, another tool in my toolbox.  My framework sometimes uses
> classes where there is only a single instance of the class, for example the
> framework class itself.  Using this new tool I can simply use the default
> instance instead of dim / instantiate / reference.
>
> I'm jazzed!
> --
> John W. Colby
> Colby Consulting
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>