I thank you for your answers and solutions. Before I wrote, I tried to use QMetaType::create function to instantiate an instance but since QObject have deleted copy constructor and copy assignment operator, I have ended up using QObject pointer with QMetaType.. And when I see that QMetaType::create() function, it just create a pointer to QObject but not the QObject instance.. So I thought QMetaType is not for the QObject-derived classes..
But I have not realised that QMetaType::metaObjectForType function returns QMetaObject instance for the class not for the pointer to class. For now there is a design choice which I feel weak myself, to do factory or to use QMetaType for creating instances. Thank you, Sina 2016-03-01 18:51 GMT+02:00 André Somers <an...@familiesomers.nl>: > > > Op 01/03/2016 om 17:21 schreef Thiago Macieira: > >> On terça-feira, 1 de março de 2016 17:06:49 PST André Somers wrote: >> >>> The meta *object* system has no registration. >>>> >>>> The meta *type* system requires that the registered type be default- >>>> constructible and copyable, but QObject is not copyable. Therefore, >>>> QObject- derived classes cannot be registered with the meta type system. >>>> >>> Am I completely misinterpretting the documentation then? >>> http://doc.qt.io/qt-5/qmetatype.html#metaObject >>> >>> If I read that correctly, you can register a >>> pointer-to-a-QObject-derived-class-instance and use that. So, indeed, >>> you do not register the type, but the type*. And that has no problems >>> with being default constructed or copied. >>> >> Correct. You can't register a QObject class with the meta type system, >> but you >> can register a pointer to a QObject class. The problem is that >> QMetaType::create() will then create a pointer, not the object. >> > Of course. But... Again, if I read it correctly, you *can* then get the > QMetaObject from QMetaType, and using that, you can create an actual > instance. > > Just tested this trivial example: > > //main.cpp > int main(int argc, char *argv[]) > { > qRegisterMetaType<TestClass*>(); //this could be elsewhere of course > > QCoreApplication a(argc, argv); > > auto tId = QMetaType::type("TestClass*"); //just using the class name > with an * > auto metaObject = QMetaType::metaObjectForType(tId); > QObject* instance = metaObject->newInstance(); > > return a.exec(); > delete instance; > } > > //testclass.h > class TestClass: public QObject > { > Q_OBJECT > > public: > Q_INVOKABLE TestClass(); > }; > > Q_DECLARE_METATYPE(TestClass*) > > //testclass.cpp > TestClass::TestClass() > { > qDebug() << "TestClass instance created"; > } > > Which prints out "TestClass instance created" on the console. My > conclusion is that it works, and that you _can_ create a QObject derived > instance with just the class name. > > Again: I am not claiming that abusing this to skip defining a factory is a > good idea. Just that it is possible. > > > André > > > _______________________________________________ > Interest mailing list > Interest@qt-project.org > http://lists.qt-project.org/mailman/listinfo/interest >
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