QVariant custom type returning QVariant::QPaintBufferCacheEntry

Erakis

Hi,

I'm having problem getting custom type name from a QVariant using a QtQuick project on Qt 5.4.1

class MyClass : public QObject
{
    Q_OBJECT
}
Q_DECLARE_METATYPE(MyClass)

class MyClass2 : public QObject
{
    Q_OBJECT
}
Q_DECLARE_METATYPE(MyClass2)

Now in the main.cpp :

class MyClass1 : public QObject
{
    Q_OBJECT
}
Q_DECLARE_METATYPE(MyClass1)
 
class MyClass2 : public QObject
{
    Q_OBJECT
}
Q_DECLARE_METATYPE(MyClass2)
 
// Now in the main.cpp :
MyClass1 v1;
QVariant t1 = QVariant::fromValue(v1);
MyClass2 v2;
QVariant t2 = QVariant::fromValue(v2);
 
qDebug() << t1.type();  // Return QVariant::QPaintBufferCacheEntry
qDebug() << t2.type();  // Return QVariant::QPaintBufferCacheEntry
 
qDebug() << t1.userType();  // Return 1060
qDebug() << t2.userType();  // Return 1060
 
qDebug() << qMetaTypeId<MyClass1>();  // Return 1060
qDebug() << qMetaTypeId<MyClass2>();  // Return 1061

Now, how can I compare if t1 is the same type as t2 if both are returning the same type ID ?

It is a bug ? If yes, then is there a workaround to get the correct type ? I want to put element of "MyClass" and "MyClass" inside a QVariantList and while browsing the list do specific work according the type of the object.

The only workaround I found for now is having a base class "MyClassBase". Next derivate "MyClass" and "MyClass2" from the "MyClassBase". The "MyClassBase" could have a virtual method GetCustomType(). But I'm a bit disappointed that QT metatype does not seem to work here.

Best regards,

SGaist

Hi,

// qRegisterMetaType<MyClass >("MyClass1");
// qRegisterMetaType<MyClass >("MyClass2");

Looks like you are calling qRegisterMetaType twice for the same class

Erakis

Yes but I forget to remove this code before pasting. Sorry. Moreover it is not part of the question. I remove it from the original question

Erakis

Hi,

I create a class derivated from QAbstractListModel and I need to put it into a QVariantList. Forcing me to use the Q_DECLARE_METATYPE macro as if I well understand everything we put inside a QVariant need to be declared with Q_DECLARE_METATYPE.

But I read on QT documentation that "All Qt classes are noncopyable by deriving from QObject.". Obviously QAbstractListModel derived from QObject !

So I'm in the obligation to provide 3 things :
1 - Public default constructor
2 - Public copy constructor
3 - Public destructor

Here is my implementation :

class CVariable : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString text READ text WRITE setText NOTIFY textChanged)

public:
    explicit CVariable(QObject *parent = 0);
    explicit CVariable(const QString& text, QObject *parent = 0);
    CVariable(const CVariable& copy);
    ~CVariable();

public:
    QString text() const;

signals:
     void textChanged(const QString& newText);

public slots:
    void setText(const QString& text);

private:
    QString  m_text;
};
Q_DECLARE_METATYPE(CVariable)


class CVariableList : public QAbstractListModel
{
    Q_OBJECT
    Q_PROPERTY(int count READ rowCount NOTIFY countChanged)

public:
    enum InterfaceVariableListModelDataRole
    {
        TextRole = Qt::UserRole + 1
    };

public:
    CVariableList(QObject *parent = 0);
    // Basing on QT documentation I would need to declare a copy constructor here to get thing work with Q_DECLARE_METATYPE.

    int rowCount(const QModelIndex &parent = QModelIndex()) const;

    QVariant data(const QModelIndex &index, int role = TextRole) const;

    void addVariable(CVariable* pVariableInfo);

    CVariable* getVariable(int iRow);

    void issueRowCountChangeEmit(int iRow);

protected:
    QHash<int, QByteArray> roleNames() const;

signals:
    void countChanged(int iNewCount);

private:
    QList<CVariable*>      m_VariableList;
};

Q_DECLARE_METATYPE(CVariableList)

I have to keep a list that can contain either a CVariable* or CVariableList*. The only way I found is to use a QVariantList. However while browsing this list I have to distinguish the element (CVariable* or CVariableList*). I was counting on the help of :

for ( QVariantList::const_iterator it = list.begin(); it!=list.end(); ++it )
{
       if ( qMetaTypeId<CVariable *> == i>userType() )
      {
              ....
      }
}

But unfortunately

QVariant::fromValue(&myVariable).userType()

is returning the same meta ID as

QVariant::fromValue(&myVariableList).userType()

It is a bug or there something I do not understand ?

Best regards,

SGaist

Both are pointers to QObject that's why you get the same ID.

Note that what you are currently doing is wrong. QObject is not copyable