Re: GtkAda's "On_Edited"

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2022-05-30 09:46, John Perry wrote:
>> On_* procedures are useless most of the time.
> 
> I guess you mean in GtkAda?

Yes.

> I've found them invaluable in other contexts. If so, that's disappointing. To be fair, in the hours of reading on this I did notice that Gtk+ itself makes this difficult; the On_* procedures seem to be a GtkAda enhancement.

Yes, GtkAda adds a typed layer on top of untyped GTK signals.

> In the end I made it work with an On_* design, but it was your suggestion that helped! I used the second form of On_Edited and passed a TreeView in the slot. To get the model:
> 
>        Tree_View: Gtk_Tree_View := Gtk_Tree_View(Self);
>        Model: Gtk_Tree_Model := Get_Model( Tree_View );
>        Iter     : Gtk_Tree_Iter := Get_Iter_From_String(Model, Path);
>        Store: Gtk_List_Store := Gtk_List_Store( To_Object(Model) );
> 
> Getting the rest wasn't too hard after I had that. What I hadn't understood at first was that the Model had to be converted from the Interface via the To_Object function.

If that is OK to you, but in production code you need a lot of stuff to 
do in a handler, most of it is unrelated to the tree view. This is why a 
custom widget is always advisable. Using a slot is a matter of taste/ I 
never use slots and avoid run-time type conversions.

BTW, derived widgets is also a GtkAda feature, in GTK a derived widget 
require a lot of work. In GtkAda they are trivial.

Typically in a renderer edit commit you would maintain undo/redo 
buffers, change the active cell for smooth navigation, [un]gray/hide a 
couple of buttons (like Save). Same goes with the buttons and basically 
with all signals.

The design pattern you need to keep in mind is that a signal sent to a 
visual element like renderer or button, logically, is rather sent to 
some container widget a couple layers above. If you do not follow this 
logic, you will have a very complicated fragile code.

> PS If anyone knows how to make the first form of On_Edited work, I'd be delighted to know.

The first form can be used with a static layout and global variables. (:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de