Can I expose a C++ model as Q_Property?

maxwell31

Hi,

I have a QAbstractListModel which is member of a QObject class. Can I expose the model as a Q_Property to QML?

sierdzio

Yes, here is some help: https://doc.qt.io/qt-5/qtquick-modelviewsdata-cppmodels.html.

maxwell31

my problem here is the following:

I write my custom plotting component (a QQuickItem). I might have several instances of these plots in my application, and each object has its own model, e.g. for the x-ticks.

I guess using

ctxt->setContextProperty("myModel",_tickModel);

will not work as I will have several instances, and the name would then not be unique. Doing

    qmlRegisterType<TickModel>(uri, 1, 0,
            "TickModel");

would allow me to create the model in qml, but it should be created in C++. Would using qmlRegisterType allow me to do something like this?:

class Plot : public QQuickItem {
    Q_OBJECT
public:
 Q_INVOKABLE TickModel getTickModel()

KroMignon

@maxwell31 said in Can I expose a C++ model as Q_Property?:

Would using qmlRegisterType allow me to do something like this?:
class Plot : public QQuickItem {
Q_OBJECT
public:
Q_INVOKABLE TickModel getTickModel()

qmlRegisterType() will allow you to create a new instance of the given class. If you don't need to create an instance I would suggest you to do it like this:

class Plot : public QQuickItem {
    Q_OBJECT
public:
 Q_INVOKABLE QObject* getTickModel();

But be aware that if the TickModel object did not have a parent, QML engine will take ownership and delete it when QML did not need it anymore.

Gojir4

@maxwell31 Hi,
is dataList really an instance of QAbstractItemModel ?
If yes, why are you wrapping your model with QVariant::fromValue() ?

Better to do:

ctxt->setContextProperty("myModel", dataList);

Or share an object which share the model as property:

class MyClass: public QObject
{
    Q_OBJECT
    Q_PROPERTY(MyModel* model READ model)
...
}

By this way you will have access to the interface of QAbstractItemModel (MyModel) from QML side (auto-completion)

maxwell31

@Gojir4 said in Can I expose a C++ model as Q_Property?:

is dataList really an instance of QAbstractItemModel ?
If yes, why are you wrapping your model with QVariant::fromValue() ?

Sorry, I just copied from the documentation. I corrected my post

maxwell31

Exposing the model like this

class MyClass: public QObject
{
    Q_OBJECT
    Q_PROPERTY(MyModel* model READ model)
...
}

works fine.

maxwell31

@Gojir4 said in Can I expose a C++ model as Q_Property?:

Better to do:
ctxt->setContextProperty("myModel", dataList);

would this also work if I have several instances?

Pradeep P N

Hi @maxwell31

You can also try with qRegisterMetaType.

Q_PROPERTY(MyModel* model MEMBER m_Model NOTIFY modelChanged)

then

qRegisterMetaType<MyModel *>();

All the best.