[Solved]QApplication static linkage and plugins

[jpalbertini]

Hi everyone,

I build a Main App/plugin application using qt 5.1 for multi platform purpose.

In windows, the Main app is statically linked whereas the plugins are dynamically linked (the first one is a requirement, the second more of a choice :) )

Up until now, everything worked fine.

Now I want the plugin to be able to show some stuff (mostly configuration...) and everything is not working fine on windows. When I intend to show something i got a "QWidget: Must construct a QApplication before a QPaintDevice". after a little bit of research, i understand that everything relying on a UI must have a instance of QApplication running, so qApp should not be NULL, but it is with my plugins but not my main app.

Anyone knows how to set/assign a QApplication ?

thanks in advance :)

[raven-worx]

basically you have nothing to do other than creating an QApplication instance.

But to get you right:
Your main app is linked statically against all Qt libs. Only your plugin is loaded dynamically? And this plugin also uses Qt stuff?

[jpalbertini]

thanks for your reply,

if it is possible I prefer to not create a QApplication, but rather use the one from my main application if possible...

But yes only my plugins are loaded dynamically and yes they use non-ui Qt stuff

[raven-worx]

[quote author="jpalbertini" date="1383577128"]
But yes only my plugins are loaded dynamically and yes they use non-ui Qt stuff[/quote]
So how do you link your plugin binary against Qt?
And what does your plugin do exactly? Doesn't sound like it's non-ui stuff when a QPaintDevice is required...

[jpalbertini]

my plugins are dynamically linked against qt

basically i got two plugin, one which sends arrays of data, the other one sends QImages

[raven-worx]

so this means your application runs with 2 different Qt binaries...

You should have created a QApplication in your main app, right?

I still don't know where you are missing the QPaintDevice...

But nvertheless you shouldn't mix statically and dynamic linked binaries. Either way link all dynamically or statically. I would suggest you also link your "plugins statically":http://qt-project.org/doc/qt-4.8/plugins-howto.html#static-plugins.

[jpalbertini]

one thing I also forgot to mention is that I have another app, which is dynamically linked against Qt that work fine and plugins can send QImages directly without a problem.

So my thoughts are that the QCoreApplication::self value is not pass correctly to the plugin with a statically linked app (the qApp macro is NULL)

[raven-worx]

sure it is, when you link your plugin against the dynamically linked version of Qt wherein the QApplication object never gets initialized.

[jpalbertini]

Is there a way that I assign it myself ? the self and init() are marked as private so my range of action is kinda limited, without having to rebuilding Qt with some sort of a setInstance method...

[raven-worx]

no ... and don't do it!
You do want to assign a object from a statically linked address space into a dynamically linked one...
Doing this you will probably run into another problem sooner or later.

And also that your application needs 2 Qt distributions doesn't make sense don't you think?

Link your plugins also statically and you should be fine.

[jpalbertini]

ok thanks i'll do that