Get a c++ object in QML and use it in javascript

Question

I'm making an application in which I'd like to call a function from QML in C++ source, and that c++ function to return me and object which I can use it with the same properties in the javascript part of QML. I've made the connection and everything. I've tried to send a QVariantMap and tried to use that object in javascript, but I don't get the properties of that object

So at this stage your QML recognizes the c++ objects, correct? Did you create read and write functions for the elements you want to access? — kmdent
– kmdent, Commented Jul 21, 2011 at 17:17
I have something like this, this c++ method to return a qvariant map QVariantMap Mediator::initialize() { vector<Node*> table; Mediator m; Node TestNode("1", table); QVariant test = QVariant::fromValue(TestNode); QVariantMap map; map.insert("1",proba); return map; } and later in the javascript source I have: function foo(anObject) { console.log(anObject.getId()); } So I want to call a methods from that object. So far if I try to access the map it only prints "QVariant(Node)" Sorry for the unformatted text — nikolakoco
– nikolakoco, Commented Jul 22, 2011 at 9:24
Are you sure the object is returned correctly? I personally haven't seen any samples with functions returning object instances (I could be wrong). Also I believe any objects exposed to qml need to inherit from QDeclarativeItem and registered with qml... Finally, if it all works ok and you get the correct instance back I would expect to get the object's id via the id property : anObject.id (not the underlying getter function) — George
– George, Commented Aug 10, 2011 at 7:35

bstpierre · Accepted Answer · 2011-12-19 15:05:03Z

3

There are two ways for exporting QObject based types from C++ to QML:

Return standalone QObject directly from property READer or Q_INVOKABLE function. Note, object returned as a property has C++ ownership, Q_INVOKABLE-object has JS ownership. You can change this default behaviour via http://doc.qt.nokia.com/4.7/qdeclarativeengine.html#setObjectOwnership.
Return array of QObjects. In that case you should use QObjectList, QDeclarativePropertyMap (not QVariantMap) or QAbstractListModel.

edited Dec 19, 2011 at 15:05

bstpierre

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answered Dec 19, 2011 at 14:35

Pavel Osipov

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blakharaz · Accepted Answer · 2011-12-15 23:42:09Z

1

Your classes to be exposed have to inherit from QObject (or QDeclarativeItem if they are UI components) and you will have to register their types in your main() or in a Qt plugin before loading the QML code.

Have a look at http://developer.qt.nokia.com/doc/qt-4.7/declarative-tutorials-extending-chapter1-basics.html

answered Dec 15, 2011 at 23:42

blakharaz

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JaakkoK · Accepted Answer · 2011-12-14 14:49:21Z

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To pass an object from C++ to QML as a function return value, the return value type needs to be QVariant, not QVariantMap, even though that is the type in the C++ code. So just change your initialize function signature to

QVariant initialize();

without changing anything else, and then you can access the properties.

Regarding your later comment on wanting to call methods on that returned object, that is not possible; the returned object is just a set of name-value pairs. If you want the object to have, say, an id property, you need to insert a value with that key to the QVariantMap in C++ before returning it.

answered Dec 14, 2011 at 14:49

JaakkoK

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