Can I subclass QEvent?

Question

I tried to make a class which is a subclass of QEvent, but I got error after building.

My steps,
1. Create a project using Qt console template
2. create the following code

#ifndef MYEVENT_H
#define MYEVENT_H

#include <QEvent>
#include <QObject>

class MyEvent : public QEvent
{
    Q_OBJECT
public:
    explicit MyEvent();

signals:

public slots:
};

#endif

---

//CPP File
MyEvent::MyEvent() :
    QEvent(QEvent::User)
{
}

---

moc_MyEvent.cpp:70:21: error: invalid use of non-static data member 'd_ptr'
    return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
           ~~~~~~~~~^~~~~
moc_MyEvent.cpp:70:21: error: 'd_ptr' is a protected member of 'QObject'
../../../../../../Qt5.1.0/5.1.0/clang_64/include/QtCore/qobject.h:411:33: note: declared protected here
    QScopedPointer<QObjectData> d_ptr;
                            ^

---

Qt5
Mac OSX 10.8.4

---

How do I solve it and why? Thanks.

Answer 1

Dcow gives corrent answer.

Your mistake is that QEvent does not inherit from QObject, and you try to do it. You should not use Q_OBJECT macros or you should interhit your class from QObject too. But it's dark side.

Answer 2

First of all WHY? You should write why you need this, I'm sure that your problem solution which you are trying to fix is just wrong!

Secondly problem is Q_OBJECT macro. QEvent is not a QObject so this macro is not applicable and this is why you have this error.

Answer 3

As already pointed out: No Q_OBJECT. But let me add something and point your attention to a rarely used and widely unknown macro: Q_GADGET

Almost a Q_OBJECT for non-QObjects.

From the Qt Docs:

Use Q_GADGET instead of Q_OBJECT to enable the meta object system's support for enums in a class that is not a QObject subclass. Q_GADGET makes a class member, staticMetaObject, available. staticMetaObject is of type QMetaObject and provides access to the enums declared with Q_ENUMS. Q_GADGET is provided only for C++.

Comes handy from time to time.