How to create a QML type?

Question

Qt

It is necessary to create models of a group of physical bodies with the ability to edit their parameters without recompilation. I decided to use QML for this business - a convenient syntax, you can declare functions for a specific calculation of parameters. Everything is cool, but I would like to move away from Quick as much as possible.
Created 2 classes:

class Model : public QObject
{
    Q_OBJECT

public:
    explicit Model(QObject *parent = Q_NULLPTR);
}

class Anode : public QObject
{
    Q_OBJECT

public:
    explicit Anode(QObject *parent = Q_NULLPTR);
}

Registered types in main.cpp :

int main(int argc, char *argv[])
{
    qmlRegisterType<Model>("Model", 1, 0, "Model");
    qmlRegisterType<Anode>("Model", 1, 0, "Anode");
    // ...
}

I create a QML file:

import Model 1.0

Model {
    Anode {
    }
}

Download qml file:

QQmlEngine engine;
QQmlComponent component(&engine);
component.loadUrl(QUrl("types/type1.qml"));
QObject *myObject = component.create();

I get an error: QQmlComponent: Component is not ready
I load it differently:

QQmlApplicationEngine engine;
engine.load(QUrl("types/type1.qml"));

I get an error: types/type1.qml:4 Cannot assign to non-existent default property
Well, what is a default property whose name is not displayed in the debug?
It is worth removing the Anode object from the Model, how everything works.
Okay, I add Q_PROPERTY(Anode* anode READ anode WRITE setAnode NOTIFY anodeChanged) to the Model and edit the qml file:

import Model 1.0

Model {
    anode: Anode {
    }
}

I get an error: types/type1.qml:4 Unexpected object assignment
If both of these objects are inherited not from QObject , but from QQuickItem , then everything will work, but I don't need Item with all its x, y, width, height, etc. ., especially given that these parameters will be overridden by some model entities. How to defeat this Qml?

Answer 1

Ok, I figured this out:

Model {
    anode: Anode {
    }
}

It was necessary to additionally declare types through the QML_DECLARE_TYPE macro:

QML_DECLARE_TYPE(Model)
QML_DECLARE_TYPE(Anode)

But with this the error still persists...

Model {
    Anode {
    }
}

Looks like some magic macro is needed :)
Very tricky Qt! Climbed into QQuickItem and peeped what he has there ... And he has the Q_CLASSINFO macro involved.
In general, the problem was solved by adding a macro like this:

class Model : public QObject
{
    Q_OBJECT

    Q_PROPERTY(Anode* anode READ anode WRITE setAnode NOTIFY anodeChanged)

    Q_PROPERTY(QObject* item WRITE addItem)
    Q_CLASSINFO("DefaultProperty", "item")

public:
    explicit Model(QObject *parent = Q_NULLPTR);

public slots:
    void addItem(QObject* item);
}

When an Anode object is created, the Model::addItem method is called . And there you can already set the Anode object as the parent of the Model object.

Answer 2

It seems to me that you are trying to use QML in a non-standard way, so you have to immediately climb into the jungle. To begin with, I advise you to read this series of articles: https://habrahabr.ru/post/181712/