On 1/11/2016 12:53 AM, Bo Thorsen wrote:
Den 10-01-2016 kl. 03:21 skrev mark diener:
Hello List:
I have a couple of core QMLEngine questions:
Basic Code Snippet:
QQmlEngine geng ;
QQmlComponent gcomp(&geng)
gcomp.setData( ByteArrayofQML , QUrl() ) ;
gcomp.create() -> Show the QML in the QML Engine
if (gcomp.isError() == false) -> we have visible QML!
1) How does one cause all properties in the root context for QML
engine be triggered to re-evaluate their bindings again. For example
Text { text: gvariable }, it want text object to re-fetch its own
values instead of pushing values with Qobject->setProperty(). Generic
pull instead of specific push.
Can I cause a disturbance in the QmlContext and that would trigger and
"expensive" refetching of text values for example.
On one hand, this question doesn't make sense. QML vars are considered
changed immediately, and that's a basic design choice.
OTOH, it's very simple to do this yourself. Just create a function
that pulls in the new variable values. You might need a proxy object
between the real value place and the QML land, but other than that you
need no tricks for it.
2) How does one clear out everything loaded in the root QmlEngine
context?
What is the best way to clear the root context of qmlengine of
everything prior to calling
gcomp->setData() and gcomp->create( ) to load brand new QML into the
QmlEngine?
geng->clearComponentCache() ? Does this really flush everything out
regardless of anything that is currently visible on-screen?
I do not want to build up a pile of QObjects in the engine, I want
them cleanly flushed out.
Again, there are ways you could do this. Store the set of accepted
vars and values and reset to exactly those when you want, for example.
But this idea smells badly of a fundamentally bad design. If you need
to get rid of variables, reset them, etc. then they probably shouldn't
be stored as context on the root engine. This sounds like one of the
"how do I do B" because you are doing "A" already questions, and the
problem is that "A" is wrong. We get those on this list all the time.
One idea I have used often is to have a backend object that is almost
the only object exposed to QML. Inside this one you can set variables
on the fly as you want. With the very limited amount of info you have
given here this seems like a much more appropriate direction for you.
Bo Thorsen,
Director, Viking Software.
Bo:
Sorry if my information was limited.
What I was trying to say was that for the QMLEngine when it loads and
displays QML ( component setData()/create() ), I want to trigger in a
generic way an update to that information.
For example, when I change language from English to Spanish, I want the
QMLEngine to re-fetch all of its bound values in a generic way, not
specific hard coded setProperty( objectName,"text") calls to trigger.
That is a maintenance and code pattern nightmare. We need some generic
way from C++ to trigger QML value re-fetch as if the
With respect to QmlEngine->clearComponentCache(), your appreciated
answer is tied to variables and that is not what I was asking. When I
change screens, I want to dump the loaded QML and replace with new QML.
The documentation does not give me a firm grasp of the relationship to
C++ QQmlContext, QQmlEngine, and QQmlComponent.setData()/Create().
Now the 2 questions are related in that I could either "Update" the
currently displayed QML when I change languages. Or I can Dump the QML
and reload it with the new language values.
Yes, I know Qt Translation exists, but that is not the point of the
inquiry here, since I used a different design for my international support.
Cheers,
md
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