Undo and CanUndo in TMemo
lazarus / 31-LCL

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lucamar · 2018-09-01 18:00

The environment
Lazarus 1.8.4 (GTK2) / FPC 3.0.4Kubuntu 14.04 / Ubuntu 10.10The
program
It's a very simple program: just a form with a TMainMenu, a TMemo,
some actions and little else. In the main menu there is---among others
---a top-level item "Edit" with a submenu of items "Undo, "Cut",
"Copy", "Paste", etc.

The handlers for items "Edit" and "Undo" are these:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TMain.itEditClick(Sender: TObject);begin  itEditUndo.Enabled :=
Memo.CanUndo;  {itEditRedo.Enabled := False;}{ No redo for the
wicked!? }  itEditCut.Enabled := (Memo.SelLength > 0) and (not
Memo.ReadOnly);  itEditCopy.Enabled := (Memo.SelLength > 0); 
itEditPaste.Enabled := (not Memo.ReadOnly) and                       
 Clipboard.HasFormat(CF_Text);  {... etc. sniped for the forum
...}end; procedure TMain.itEditUndoClick(Sender: TObject);begin 
Memo.Undo;end;
The problem
Whatever I do: type, paste, delete, etc. Memo.CanUndo is always false.
Even if I comment out the line:

    itEditUndo.Enabled := Memo.CanUndo;

and keep the item itEditUndo always enabled, Memo.Undo, of course,
does nothing.

The question(s)
Is this some bug (in GTK, perhaps)? As designed? Fixed somewhere?
Can't (or will never) be fixed? Am I going mad?

The notes
I seem to remember that this worked on Windows, but I can't test ATM
because my Windows boxes are undergoing surgery.

Any help, anyone?

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Handoko · 2018-09-01 18:32

I remember there were some discussions about it. I didn't follow the
discussions, maybe you can find something useful from them:

https://forum.lazarus.freepascal.org/index.php/topic,37484.msg251927.h
tml#msg251927

https://forum.lazarus.freepascal.org/index.php/topic,38661.msg263312.h
tml#msg263312

https://forum.lazarus.freepascal.org/index.php?topic=41279.0

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lucamar · 2018-09-01 19:46

Thanks, Handoko; I forgot the first rule of posting: search before
doing anything else 

So the answer is: it's a well known bug about which, apparently,
nobody cares enough to fix properly.

Well, I'll see what I can do to implement something like it.

Thanks again!

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taazz · 2018-09-01 22:46

Quote from: lucamar on September 01, 2018, 09:46:04 pmThanks, Handoko;
I forgot the first rule of posting: search before doing anything else 

So the answer is: it's a well known bug about which, apparently,
nobody cares enough to fix properly.
I'm under the impression that gtk is in the process of phasing out in
favor of gtk 3. In which case I would try to test with gtk3 and see if
you can convince the authors to add it on gtk3 now that its still
under development.
Quote from: lucamar on September 01, 2018, 09:46:04 pmWell, I'll see
what I can do to implement something like it.

Thanks again!
https://forum.lazarus.freepascal.org/index.php/topic,40205.0.html here
this should get you there faster.

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lucamar · 2018-09-01 23:59

Alas! I need it on Gtk2 too, so it's me for the grinding-wheel ...
although your link may make it less "grinding".
Thanks, Taaz