qobject_cast<T> in shared libraries...

[seim]

You must not have the header of T added in two .pro files' HEADERS-sections. Otherwise the Q_OBJECT macro will be moced and compiled multiple times. This would lead to multiple instances of the metaobject and the problem you noted.

Thank you, this is the key! Interface header file was included in both plugin projects and that led to 2x different static objects for "one class". Shame on me

[seim]

One more thing as a solution given by B.Poulain:

"The problem come from the declaration of the
class IObject without the macro Q_DECLARE_INTERFACE. This macro should
be used for all objects exported outside the plugin.
If you add it, everything works fine.

If you look at the declaration of Q_DECLARE_INTERFACE, it use a slightly
different approach to make qobject_cast working across library but
without being dependant of the linker."

The IObject header file has to be added in both .pro files.

Thank you all, for your posts.