[Solved] 'QVariant::QVariant': cannot access private member declared in class 'QVariant'

nwoki

// Base class
class CommandQueue : public QThread
{
    Q_OBJECT

public:
    virtual ~CommandQueue();

protected:
    void CommandQueue();
};



// Derived classes
class ReadCommandQueue : public CommandQueue
{
    Q_OBJECT

    Q_PROPERTY(bool isReadingData   READ isReadingData  NOTIFY isReadingDataChanged)


public:
    ReadCommandQueue(QObject *parent = 0);
    ~ReadCommandQueue();

    bool isReadingData() const;

protected:
    void run() override final;

private:
    bool m_isReadingData;
};


class WriteCommandQueue : public CommandQueue
{
    Q_OBJECT

    Q_PROPERTY(bool isWritingData   READ isWritingData  NOTIFY isWritingDataChanged)

public:
    WriteCommandQueue(QObject *parent = 0);
    ~WriteCommandQueue();

    bool isWritingData() const;

Q_SIGNALS:
    /**
     * signal used just to notify the CommandQueueCenter
     * to pull the new info written
     */
    void finishedWritingCommands();
    void isWritingDataChanged();

protected:
    void run() override final;

private:
    bool m_isWritingData;
};



// CommandQueueCenter has these functions
ReadCommandQueue* CommandQueueCenter::readCommandQueue() const
{
    return d->readCommandQueue;
}

WriteCommandQueue* CommandQueueCenter::writeCommandQueue() const
{
    return d->writeCommandQueue;
}

I need these objects in my QML application so i expose them like i've always done as follows:

    m_centralWidget->engine()->rootContext()->setContextProperty("ApplicationData", m_core.applicationData());
    m_centralWidget->engine()->rootContext()->setContextProperty("CmdQueueCenter", m_core.commandQueueCenter());
    m_centralWidget->engine()->rootContext()->setContextProperty("MainWindow", this);
    m_centralWidget->engine()->rootContext()->setContextProperty("ReadCommandQueue", m_core.commandQueueCenter()->readCommandQueue());

// This last line creates my error
    m_centralWidget->engine()->rootContext()->setContextProperty("WriteCommandQueue", m_core.commandQueueCenter()->writeCommandQueue());

All was fine with the "ReadCommandQueue" but when I added the "WriteCommandQueue" i got the following error:

'QVariant::QVariant': cannot access private member declared in class 'QVariant'

Any idea why this is happening? The classes are basically identical.

VRonin

Can you show the constructor of CommandQueue and WriteCommandQueue

P.S.
Unrelated to the problem at hand but still strange:
void CommandQueue(); and WriteCommandQueue(QObject *parent = 0); looks like something fishy is going on with your parent-child management but I can't be sure as you did not include the implementation

nwoki

@VRonin said in 'QVariant::QVariant': cannot access private member declared in class 'QVariant':

Can you show the constructor of CommandQueue and WriteCommandQueue

CommandQueue::CommandQueue(QObject *parent)
    : QThread(parent)
    , m_connectionStatus(ConnectorStatus::Disconnected)
{
}


WriteCommandQueue::WriteCommandQueue(QObject *parent)
    : CommandQueue(parent)
    , m_isWritingData(false)
{
}


ReadCommandQueue::ReadCommandQueue(QObject *parent)
    : CommandQueue(parent)
    , m_isReadingData(false)
{
}

I added the ReadCommandQueue as well as it didn't cost me anything to do a copy/paste

P.S.
Unrelated to the problem at hand but still strange:
void CommandQueue(); and WriteCommandQueue(QObject *parent = 0); looks like something fishy is going on with your parent-child management but I can't be sure as you did not include the implementation

Yeah, whilst removing implementation deatials i erroneously deleted the QObject *parent = nullptr . Sorry about that

VRonin

Try cleaning the project and re-running qmake, looks like the Q_OBJECT wasn't spotted by moc.

nwoki

Already did that. Same problem. That's why I can't figure out this error. All the right pieces are in place. (Well, apparently not..)

VRonin

The problem is that setContextProperty is calling the QVariant overload instead of the QObject one and QVariant(void*) is private. QVariant::fromValue(m_core.commandQueueCenter()->writeCommandQueue()) should solve the copilation but unsure if it's ok

nwoki

Yeah, it should be calling the QObject* overload. For now the issue has been fixed with a cast

m_centralWidget->engine()->rootContext()->setContextProperty("WriteCommandQueue", (QObject*)m_core.commandQueueCenter()->writeCommandQueue());

but does anyone know why the wrong overload is being called?

VRonin

Does main() (or wherever you call setContextProperty from) know WriteCommandQueue is a QObject? i.e. did you include writesommandqueue.h or is it just forward declared like class WriteCommandQueue;?

nwoki

@VRonin said in 'QVariant::QVariant': cannot access private member declared in class 'QVariant':

Does main() (or wherever you call setContextProperty from) know WriteCommandQueue is a QObject? i.e. did you include writesommandqueue.h or is it just forward declared like class WriteCommandQueue;?

alt text

I forgot the inclusion.. Was convinced I had already done it. Thanks