[Development] QProperty and library coding guide
andre at familiesomers.nl
Wed Jul 22 13:52:58 CEST 2020
On 16-07-2020 17:40, Volker Hilsheimer wrote:
> We need “text” to be a public member of QAction, otherwise we can’t do
> That ‘text” member is a struct with a bunch of operators overloaded, so that we can do either
> qDebug() << action->text();
> qDebug() << action->text;
> action->setText(“foo”); // no binding
> action->text = document->title; // still no binding
> action->text = Qt::makePropertyBinding(document->title); // yay binding!
Thank you for this example of how these new properties are going to look
from a user code perspective. I have some questions left if you don't mind?
First, say I have another QProperty that has a binding to this
action->text property. I assume that doing `action->setText("foo")` or
`action->text = document->title()` will both result in this binding
being triggered, and thus, triggering side-effects? I would expect such
in the first case, but not so much in the second as this _looks_ like an
assignment to a member variable.
Second, say that I initialized action->text like you do in your last
example, creating a binding. And then I assign to it using, say,
`action->text = document->title();` Does that work? Do we overwrite the
binding? Is it possible to prevent that override? This was a problem in
QML as well where one could accidentally overwrite bindings. I assume
there is a way to mimic adding `readonly` like you can in QML?
Third, you show that `qDebug() << action.text()` and `qDebug() <<
action.text` is the same. Is that really all that desirable? Somebody
already pointed out this issues with doing an `auto actionText =
action.text();` elsewhere in this thread, and I am wondering if you'd
not want to output some debug info on the property itself, in stead of
just the value?
Don't get me wrong: I think the syntax where you're basically able to
use the property as if it was a member variable, basically coming back
full circle. But I also think it may be confusing for everyone expecting
an assignment to something that looks like a member to, well, behave
like that. Is there a reason why this setup was chosen over a more
conventional but admittedly less cool:
qDebug() << action->text.get();
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