Qt-interest Archive, July 2007
Re: [Qt4.3] Compile Error on Q_OBJECT in grandchild?
Message 1 in thread
Hi,
> This was hard to track down, because the qobject_cast<> in another file triggered the compile error in the "MyC" header.
What was the complete error message? Didn't it refer to the other file at all?
--
[ signature omitted ]
Message 2 in thread
Using sender() in this way is absolutely ok. (and no, you don't need to
do it the ugly reinterpret_cast-way)
again, using Qt 4.3.0 and MSVC 2003 this code compiles fine:
---------------------------
#include <QtGui>
class MyA : public QWidget {
Q_OBJECT
// ...other stuff
};
class MyB : public MyA {
Q_OBJECT // doesn't matter if here or not
// ...other stuff
};
class MyC : public MyB {
Q_OBJECT // <--- COMPILE ERROR
// ...other stuff
};
class SomeClass : public QWidget {
Q_OBJECT
public slots:
void myslot_doSomething(const QAbstractButton& /*button*/);
};
void SomeClass::myslot_doSomething(const QAbstractButton& /*button*/)
{
// ...TRIGGERS COMPILE ERROR IN "MyC.hpp" IN 4.3,
// COMPILES AND RUNS FINE IN 4.2...
MyC* myc_sender = qobject_cast<MyC*>(sender());
}
---------------------------
i suggest you create a minimal, compilable example that shows the error.
Cheers,
Peter
Charley wrote:
> Ok, strange -- I've found the trigger for the compile error (see
previous
> message below for context):
>
> void SomeClass::myslot_doSomething(const QAbstractButton& /*button*/)
> {
> // ...TRIGGERS COMPILE ERROR IN "MyC.hpp" IN 4.3,
> // COMPILES AND RUNS FINE IN 4.2...
> MyC* myc_sender = qobject_cast<MyC*>(sender());
> // ...do stuff
> }
>
> Now the previous thread makes sense: Qt4.3 is apparently a bit more
> strict regarding qobject_cast<>. However, I expected it to work
because
> it's single inheritance from QObject (through QWidget), and I have a
> Q_OBJECT in each header all-the-way down the hierarchy.
>
> This was hard to track down, because the qobject_cast<> in another
file
> triggered the compile error in the "MyC" header.
>
> (I understand using "sender()" isn't very graceful, but it seemed to
be
> useful in this case, and I found the code snippet in a Qt example --
is
> this use deprecated in Qt4.3?)
>
> Looking into QObject.h, it appears the trolls in Qt4.3 use a syntax
closer
> to the following:
>
> reinterpret_cast<T>(0)-
> >qt_check_for_QOBJECT_macro(*reinterpret_cast<T>(object));
>
> What's the appropriate way in Qt4.3 to get the user-type'd "sender()"
> within a slot?
>
> Thanks!
>
> --charley
--
[ signature omitted ]
