Access QList from qml

Question

I want to access a QList from qml. Here is a sample code

class A;
class B : public QObject {
   ...
   Q_INVOKABLE QQmlListProperty<A> read();
   ...
private:
   QList<A*> lst;
}

I'm using context property to access object of class B in qml. How can I access the list in qml. Any sample code will be helpful.

Possible duplicate: http://stackoverflow.com/questions/14287252/accessing-c-qlists-from-qml — GPPK, Mar 16 '15 at 18:48

dtech · Accepted Answer · 2015-03-16T19:35:27.360

3

You will need to Q_DECLARE_METATYPE(A *) to be able to wrap it in a QVariant for use in QML.

But that's just for referring to and passing it around QML.

If you want to use A in QML as in C++, it will have to inherit QObject and implement properties, slots and such.

You can see how to implement the QQmlListProperty here: http://doc.qt.io/qt-5/qtqml-referenceexamples-properties-example.html

Also, if QObject is too heavy for you and impractical to have a lot of them, you can always use a single QObject derived to work as a controller for a non-QObject but still registered as metatype type.

class A {
public:
  int a;
};

Q_DECLARE_METATYPE(A *)

class AProxy : public QObject {
  Q_OBJECT
public slots:
  int a(QVariant aVar) {
    return aVar.value<A *>()->a;
  }
  void setA(QVariant aVar, int v) {
    aVar.value<A *>()->a = v;
  }
};

This way you don't have the size overhead and limitations of QObject for every object in the list, and can instead use a single controller to access the data, albeit at lower performance. In your case you could use B to act as both container and controller proxy for A.

edited Mar 16 '15 at 19:35

answered Mar 16 '15 at 19:11

dtech

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I got you point, but still confused. How to implement `QQmlListPorperty` ? Do I use `property var lst: b.read()` in qml. From Qt documentation it looks like they are appending list from qml, but I want to read list from qml. – Vedanshu Mar 17 '15 at 06:37
@Ansh - did you manage to do it? I see you accepted the answer. The documentation is actually pretty thorough on how to implement it - if you want to use it from QML just declare the AppendFunction, CountFunction, AtFunction and ClearFunction as slots or `Q_INVOKABLE`: http://doc.qt.io/qt-5/qqmllistproperty.html – dtech Mar 18 '15 at 02:22
Actually I was able to implement the controller function as you suggested, that's why I accepted the answer. But the documentation is confusing be with `QQmlListProperty`. Let me explain where I'm getting confused. I'm using `read()` function to convert `QList` to `QQmlListProperty`, so in the qml I should be using it in a function like this `var lst = b.read();`(where `b` is an object of class B set as context property). But I don't think var can handle `QQmlListProperty `. – Vedanshu Mar 18 '15 at 05:29

Access QList from qml

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