Op 07/07/2016 om 23:52 schreef Rob Allan:
I'm part of a team that is looking at migrating an existing Windows
C++ app to Qt. The first decision is whether to use Widgets or Qt
Quick. Since Qt Quick is newer, shinier, faster, etc, that seems like
the obvious choice. However, for reasons that I won't go into here,
the vast majority of forms in our app are built dynamically in code.
This kind of approach seems easy enough with Widgets, but looks like
it could be difficult, or even infeasible, with Qt Quick. That's
because the preferred way of creating Qt Quick layouts is using QML,
and while there is an object model backing that, my impression is that
this object model is not designed to support heavy-duty creation and
manipulation of layout elements. For example, while QQuickItem is
documented, none of its derived classes are, and I believe their
interfaces may be private - so the only way to manipulate items is
using a generic "setProperty" syntax. And while there are a few
articles around that talk about accessing the Qt Quick model from C++,
such as this one
[http://stackoverflow.com/questions/31890372/add-objects-to-qml-layout-from-c],
they tend to use snippets of QML to get the job done in a rather hacky
way, and make various comments about the perils and pitfalls of trying
to manipulate the model from code.
I can't help comparing this with two other popular layout frameworks:
WPF/XAML, and Android/AXML. In both of these worlds, the markup
language and the "code-behind" class hierarchy of UI elements are
absolutely equivalent 1st class citizens. Anything you can do in XAML,
you can also do in the C# code-behind, whether it be creating
controls, changing their properties, altering layouts, etc. Likewise
in Android/AXML, I can (if I choose) create FrameLayouts,
RelativeLayouts, TextViews, etc in code, and arrange them and
manipulate them any way I like, as an alternative to creating an AXML
designer layout.
It seems very unfortunate that Qt Quick doesn't take this approach,
and that the "code-behind" experience is so limited.
Am I missing something here? Assuming I'm not, are there any plans to
make the Qt Quick class model more "open", with full documentation and
public interfaces for all relevant properties and methods?
No, you are not missing anything here. You are right that there is
currently no exposed C++ interface for QML that allows you to define
your UIs like you can from QML. I understand the reasoning for not (yet)
providing it, but it is indeed an often-requested thing and I would
apreciate one appearing. AFAIK, the main reason for not having an
exposed C++ backend is the stability that would enforce. Having only a
QML backend frees the developers from having a stable C++ backend with
binary compatibility guarantees. That is quite a burden to have for a
young technology like QML en Qt Quick.
But of course there are still several supported options available.
Xavier already mentioned one, but did you consider just generating the
actual QML on the fly and loading that? That would allow totally dynamic
forms.
Still, you may want to consider sticking with Qt Widgets. There is
nothing wrong with that approach. I don't know the needs of your
application, but most applications consisting of lots of dialogs with
buttons, line edits, drop-downs, lists, etc. Qt Widgets is just a very
good fit. It is very mature, stable and has the C++ interface you're
looking for. Where it does *not* shine is if you want performant
animations of your UI like you have mobile devices. If that's not what
you're after, then Qt Widgets may just be a better fit for you.
HTH,
André
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