C++ QML Wrappers wise or not

lukeparry

Hi everyone and happy new year,

Using Qt5.2/3. I would like to use some QObject derived classes in QML.The obvious and certainly easiest thing is to register the types with qmlRegisterType and add additional Q_INVOKABLE and Q_PROPERTYs : something like

@
class Network : public QObject
{
public:
Q_OBJECT

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

virtual void callMessage() { qDebug() << "Network::callMessage();"; this->metaObject()->invokeMethod(this, "message"); }
Q_INVOKABLE void message() { qDebug() << "Network::message();"; }
Q_INVOKABLE QObject * create(const QString &type);

};
@

My overall aim to allow override of methods (using invokeMethod) in QML and invoke these from c++ which would provide powerful funcitonality.

Ideally, I would prefer to avoid adding QML directly to the original classes. I would like to keep the class clean from QML because I may want to provide other language bindings later. I looked at c++ interface paper from

"https://www.qtdeveloperdays.com/2013/sites/default/files/presentation_pdf/QtDevDaysSFO-2013_WrappingCppForQml_final.pdf":https://www.qtdeveloperdays.com/2013/sites/default/files/presentation_pdf/QtDevDaysSFO-2013_WrappingCppForQml_final.pdf

e.g.
@
class QMLNetwork : public QObject
{
public:
Q_OBJECT

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

Q_INVOKABLE void callMessage() { this->_network->callMessage()}
Q_INVOKABLE void message() { qDebug() << "Network::message();"; }

private:
Network *_network;
};
@

I know this should work in practice, I think this would prevent me from using QML to override methods.

I thought of creating a wrapper inheriting from the original type to provide a new interface similar to Boost Python. However, I don't think this would work going from a c++ instance to a qml instance.

Does anyone have any thoughts?

Please let me know if anything needs clarifying.

Cheers,
Luke

dheerendra

May be some more details are required. I did not understand what do you mean by "using QML to override methods". What do you mean here ? You are writing a class in C++ and exposing to QML. You can create instance of these classes in QML. After this what would you like to do in QML with these instances ? This may help or some good sample on what you are trying at QML will help.

lukeparry

Hi,

So in QML, we use the Network object as a prototypes orinherit from this to modify the behaviour such as changing the message method.. e.g.

@
import myapi

Network {
id: myNetwork
function message() { console.log("calling qml Network.mymesssage()") }
}
@

If the callMessage is called from c++ for this QML Object instance, the qml message method is called.

This is trivial if it's a one-one mapping using qmlRegisterType, but using an additional wrapper I don't think I can achieve this. Maybe I'm asking too much...

jcbritobr

If you write a signal in your Network c++ class and emit it doesn't solve your problem?
@
class Network : public QObject
{
public:
Q_OBJECT

public:
Network(QObject *parent = 0);
~Network();
signals:
void message(message);
};@

so, in qml:

@import myapi

Network {
id: myNetwork
onMessage: {console.log(message)}
}@