Creating C++ objects from QML - c++

Question

In C++ model, I have QAbstractListModelderived class called Cart which contains QList<void*>container.
In QML, I show a list of objects. When user clicks on any of them, it should create that object in C++ and add it to the cart. It will also set some properties of that object.
My question is how do I really do that in the best way?
Here is the code how this will look like in C++ alone:
Cart * cart = new Cart; // we have this object already created
// which we have exposed to QML as 'qmlcart'.
// When user clicks apple
Apple * apple = new Apple(1.99) ; // 1.99 is price
apple->setType("Red Delicious");
cart.add( apple );
// When user clicks orange
Orange * orange = new Orange(0.99) // price
orange->setType("Valencia")
cart.add( orange );
The above is straight forward in C++ world but it gets somewhat complex if the click is in QML. What is the best way create and pass information about the object? Assume we have more attributes about the object other than price and type.
Does there has to be a corresponding slot function for every type of object we create? If the object has more complex properties, say 5 various attributes, do we pass all 5 of them to slot function or there is a better way? Should we use some of factory design pattern to create object?
One particular ability I am missing with QML in use is the freedom to work with C++ created object. For example if it was all C++, I could have created the C++ object and than set all its attributes no matter how many are there and than simply add the object to the container.
But with QML, even though I have all information about the object but I can't really create and configure the class and than pass to C++ because it has to be created in C++ which can't return it and so all configuration parameters will have to be passed to the slot function as well! Is there any better way?

Answer 1

Unless the C++ object happens to be a QObject derived type, registered as a type to QML, you can't do that directly. Even in QML, you either need a component or a QML source wrapper to create a C++ object, for example:
\\Object.qml
import Object 1.0
Object {}
So now you have a QML source wrapper to create the C++ Object dynamically. Or using a component:
Component {
id: component
Object {}
}
You can however, have a C++ slot or Q_INVOKABLE you can call from QML, and do the object creation there.
You can set object properties in QML as well, for example:
Object {
someProperty: someValue
}
or
component.createObject(parentObj, {"someProperty" : somevalue})
it will work similarly to a constructor - all properties will be set before the object is considered to be "competed" by the runtime.
From your question it looks like you are getting ahead of yourself - do a little more learning before you rush into using QML... and there is really no need for those void * - this is not C. Don't make your life any harder.