Error when making "QObject::connect"

Creatorczyk

Hi,

I want to create a simple class inheriting from QList but while creating the line, from connect returns an error:

Error:

C:\Qt\Qt5.12.5\5.12.5\mingw73_64\include\QtCore\qobject.h:250: error: no matching function for call to 'QObject::connectImpl(const Object*&, void**, const Object*&, void**, QtPrivate::QSlotObject<void (AssetsList::*)(), QtPrivate::List<>, void>*, Qt::ConnectionType&, const int*&, const QMetaObject*)'
         return connectImpl(sender, reinterpret_cast<void **>(&signal),
                ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                            receiver, reinterpret_cast<void **>(&slot),
                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                            new QtPrivate::QSlotObject<Func2, typename QtPrivate::List_Left<typename SignalType::Arguments, SlotType::ArgumentCount>::Value,
                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                            typename SignalType::ReturnType>(slot),
                                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                             type, types, &SignalType::Object::staticMetaObject);
                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

C:\Qt\Qt5.12.5\5.12.5\mingw73_64\include\QtCore\qobjectdefs_impl.h:414: error: invalid static_cast from type 'QObject*' to type 'QtPrivate::FunctionPointer<void (AssetsList::*)()>::Object* {aka AssetsList*}'
                 FuncType::template call<Args, R>(static_cast<QSlotObject*>(this_)->function, static_cast<typename FuncType::Object *>(r), a);
                                                                                              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

My code:

class AssetsList: public QList<Asset>{
    Q_OBJECT
public:
    AssetsList(): actionsValue(0), bondsValue(0), rawMaterialsValue(0){
        QObject::connect(this, &AssetsList::test_signal, this, &AssetsList::test_slot);
    }
    virtual ~AssetsList(){}

signals:
    void test_signal();

public slots:
    void test_slot(){
        /* do something*/
    }

private:
    float actionsValue;
    float bondsValue;
    float rawMaterialsValue;
};

How could i fix that?

jsulm

@Creatorczyk https://doc.qt.io/qt-5/qobject.html#Q_OBJECT
"Note: This macro requires the class to be a subclass of QObject. 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."
Try to change Q_OBJECT to Q_GADGET because QList is not derived from QObject.

Creatorczyk

@jsulm I changed like below:

class AssetsList: public QList<Asset>{
    Q_GADGET
public:
    AssetsList(): actionsValue(0), bondsValue(0), rawMaterialsValue(0){
        QObject::connect(this, &AssetsList::test_signal, this, &AssetsList::test_slot);
    }
    virtual ~AssetsList(){}

signals:
    void test_signal();

public slots:
    void test_slot(){

    }

private:
    float actionsValue;
    float bondsValue;
    float rawMaterialsValue;
};

But there are still errors:

error: 'qt_metacall' is not a member of 'AssetsList'
         enum { Value =  sizeof(test(&Object::qt_metacall)) == sizeof(int) };
                                     ^~~~~~~

error: static assertion failed: No Q_OBJECT in the class with the signal
 #  define Q_STATIC_ASSERT_X(Condition, Message) static_assert(bool(Condition), Message)

error: static assertion failed: No Q_OBJECT in the class with the signal
 #  define Q_STATIC_ASSERT_X(Condition, Message) static_assert(bool(Condition), Message)
                                                 ^

jsulm

@Creatorczyk My bad: "Q_GADGETs can have Q_ENUM, Q_PROPERTY and Q_INVOKABLE, but they cannot have signals or slots."
https://doc.qt.io/qt-5/qobject.html#Q_GADGET
So, my suggestion is not going to work as you want to have signals/slots.
Is there a reason why you want to subclass QList?

Creatorczyk

@jsulm I would like to inherit from QList to add my methods and to be able to pass a list to a model in a ListView in qml

VRonin

@Creatorczyk Isn't it easier if you derive from QAbstractListModel?