Beyond 2.6

John Ralls jralls at
Sat Feb 16 11:06:21 EST 2013

On Feb 16, 2013, at 5:06 AM, Herbert Thoma <herbert.thoma at> wrote:

> forgot CC list ...
> Am 15.02.2013 21:06, schrieb John Ralls:
>>>> Why hard to say? MVC isn't exactly cutting-edge design. It's been
>>>> around since 1988 and 7 years later GoF thought it so well-understood
>>>> that it's the "how to use patterns" example in the introduction.
>>> Well, the point is that every time the user leaves a field you need to
>>> parse all the input fields and process them in the controller/model as
>>> part of the validation, even if the user hasn't asked to 'save' yet.
>>> I guess it all depends on your controller APIs.  (In the RoR world this
>>> is harder to do, because the view is in the browser, but the model and
>>> controllers are on the server -- and there is no "verify this model" API
>>> in the controller.  At least not directly.  The client-side-validations
>>> gem adds some support for this).
>> We already do that for the account type listbox: We connect to a signal
>> (don't know offhand which one) in the parent accounts GtkTreeView that tells
>> us that the user has selected a parent account, retrieve that account, run
>> xaccAccountGetCompatibleTypes() on it, and populate the account type listbox
>> with the result.  
>> That's a pretty standard way for UI View objects to communicate with their
>> controller objects, though there are others. Wx has a specific "Validator"
>> class that lets you register a callback to test control input as it happens.
>> It also has a signals mechanism (which they rather confusingly call Events)
>> to support other interactivity needs. Qt is well-known for its "signals and slots"
>> feature, which I imagine is used for this purpose much like Gtk's signals are, but
>> I've never written anything for Qt so I don't actually know.
> Yes, you can use signals and slots this way. I personally like Qt very much. For me
> it is the best GUI toolkit I have ever worked with (I worked with Motif, MFC,
> GTK and Qt, but always only small projects or patches to GnuCash).
> However, I would still be hesitant to use signals and slots in the engine. Earlier
> in this thread it was stated that the engine depends heavily on Glib and that this
> is bad for portability. Do we want to replace the Glib dependency with a Qt
> dependency?

See Geert's and my responses about where the "slots" go.

Does Qt have another mechanism for validating user input as he types? How does it handle spell checking? ("Magic" is a reasonable answer here: I know in detail how Gtk handles spell checking because it's an add-on that I've contributed to, but Apple handles it inside the toolkit so that application devs needn't do anything about it.)

John Ralls

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