Re: UnDo/ ReDo Buffer ?

[Claus Dietrich <claus.dietrich@xxxxxxxxxx>]

Hi Benoít

Thanks for this giant input. I will need some time to digest it. 
Gianluigi provided me directly with a smaller sample-project which seems 
to apply this concept. This all should be a good basis to start with.

I will continue to use AI (preferably perplexity). In many cases it 
provides reasonable, compact, factual and useful answers within seconds 
which I wouldn't get in forums within hours/days. Sometimes I even 
didn't know where to ask and got immediate and brillant answers. And 
pretty often it helps me to avoid headache and plenty of time, i.e. when 
I need a complex regular expression. Its capabilities are amazing and 
rather scary than shitty.

Best regards

Claus


Am 22.08.25 um 15:17 schrieb Benoît Minisini:
> Le 20/08/2025 à 14:17, Claus Dietrich a écrit :
> > Hi
> >
> > I developed an app for scanning documents. It depicts the scans in a 
> > ListView with a thumbnail preview. The order of the scans in the 
> > ListView can be changed and scans can also be deleted. What was 
> > missing so far is an UnDo function. So I asked an AI about a suitable 
> > concept and got a reasonable proposal based on a class for scanned 
> > document and a collection of these classes and a history stack. I 
> > tested it in a pilot project and it turned out to be feasible and 
> > efficient.
> >
> > In parallel I found this in the Gambas-wiki: https://gambaswiki.org/ 
> > edit/snippets/undoredobuffer
> >
> > I don't understand this chapter. It seems to tell the reader, that 
> > there is a generic solution for any thinkable undo/redo action in an 
> > app. As this is beyond my imagination I kindly ask for some guidance 
> > resp. concepts for UnDo/ReDo functions und sample projects if available.
> >
> > Best regards
> >
> > Claus
>
> I will try to explain that concept the best I can.
>
> But please stop doing using this AI shit. Or only for questions you 
> already know the answer. 🙂
>
> To implement undo/redo, you have to list all the actions in your 
> program that are undoable. These actions must be reversible to be able 
> to be redoable.
>
> Then you create a stack of "actions", each action being an object or a 
> structure that includes all the needed information for undoing or 
> redoing the action.
>
> Then you have the following methods:
>
> - Add a new action to the stack.
> - Undo the last action.
> - Redo the action.
> - Begin a group of action that will be undone or redone globally.
> - End a group of action that will be undone or redone globally.
>
> You have an example of that with the 'CUndo' class in the IDE source 
> code. It is used for implementing undo/redo in the form editor.
>
> Now the question is: how an action can be executed (inverted or not) 
> in a generic way?
>
> This way: in the 'CUndo' class, I put the name of the public method in 
> the action data, and I use 'Object.Call()' to dynamically call the 
> method in the object passed to the Undo() or the Redo() method.
>
> So everything is entirely generic! The 'CUndo' class can be used for 
> almost anything.
>
> When a "undoable" method is called, it calls the Add() method of the 
> 'CUndo' object, passing as argument the name of the method that will 
> do the reverse action (with the arguments if needed).
>
> To see an example, look at the 'FForm.RaiseControl()' and 
> 'FForm.LowerControl()' method. They indirectly call methods in the 
> 'CControl' class that implement what I described above.
>
> The only real hard thing is being careful when describing the action, 
> the reverse action, and implementing their respective methods. They 
> must be the exact contrary!
>
> I hope it was clear enough. If you have any question, tell me.
>
> Regards,
>
> --
> Benoît Minisini.