Design thought for callbacks

[Chris Angelico]

On Sun, Feb 22, 2015 at 11:07 PM, Cem Karan <cfkaran2 at gmail.com> wrote:
>> Correct. The GUI engine ultimately owns everything. Of course, this is
>> a very simple case (imagine a little notification popup; you don't
>> care about it, you don't need to know when it's been closed, the only
>> event on it is "hit Close to destroy the window"), and most usage
>> would have other complications, but it's not uncommon for me to build
>> a GUI program that leaves everything owned by the GUI engine.
>> Everything is done through callbacks. Destroy a window, clean up its
>> callbacks. The main window will have an "on-deletion" callback that
>> terminates the program, perhaps. It's pretty straight-forward.
>
> How do you handle returning information?  E.g., the user types in a number and expects that to update the internal state of your code somewhere.

Not sure what you mean by "returning". If the user types in a number
in a GUI widget, that would trigger some kind of on-change event, and
either the new text would be a parameter to the callback function, or
the callback could query the widget. In the latter case, I'd probably
have the callback as a closure, and thus able to reference the object.

ChrisA