=== Updated question ===
You can call slots or Q_INVOKABLE methods just fine in QML to change "C++ properties" from QML. You will need to expose the C++ object as a context property though. You would need to write something like this below:
myclass.h
class MyClass : public QObject
{
Q_OBJECT
public:
MyClass(QObject *parent) : QObject(parent) { ... }
Q_INVOKABLE void myInvokable();
public slots:
void mySlot();
...
}
main.cpp
...
MyClass myClassObject;
QQuickView view;
view.rootContext()->setContextProperty("myClassContextProperty", &myClassObject;
view->setSource(QUrl::fromLocalFile("main.qml"));
view->show();
...
main.qml
Button {
...
// You can replace onClicked with your own custom signal
onClicked: myClassContextProperty.myslot()
// or
onClicked: myClassContextProperty.myInvokable()
...
}
=== Further questions in the comment ===
You would have a Q_PROPERTY in C++, and you bind that property to your property in QML, or catch the onFooChanged signal handler for the property called "foo".
myclass.h
class MyClass : public QObject
{
Q_OBJECT
Q_PROPERTY(foo READ foo NOTIFY fooChanged)
public:
MyClass(QObject *parent) : QObject(parent) { ... }
int foo() const;
public signals:
void fooChanged();
public slots:
void mySlot() { foo = 5; emit fooChanged(); };
private:
int foo;
...
}
main.cpp
...
MyClass myClassObject;
QQuickView view;
view.rootContext()->setContextProperty("myClassContextProperty", &myClassObject;
view->setSource(QUrl::fromLocalFile("main.qml"));
view->show();
...
main.qml
...
// Bind foo to bar
property int bar: myClassContextProperty.foo
=== Original question ===
It seems that you are trying to ask if you can declare the same both in C++ and QML simultaneously, i.e. some parts of it in QML and then the rest in QML.
I think you would need to register (qmlRegisterMetaType, etc) your C++ type with the Qt meta type system, and then you could use that class as an item in QML (maybe with a parent?) to achieve what you wish.
This is the relevant documentation for further reading:
Registering an Instantiable Object Type
For your convenience, here goes some code inline:
message.h
class Message : public QObject
{
Q_OBJECT
Q_PROPERTY(QString author READ author WRITE setAuthor NOTIFY authorChanged)
Q_PROPERTY(QDateTime creationDate READ creationDate WRITE setCreationDate NOTIFY creationDateChanged)
public:
// ...
};
qmlRegisterType<Message>("com.mycompany.messaging", 1, 0, "Message");
...
main.qml
import com.mycompany.messaging 1.0
Message {
author: "Amelie"
creationDate: new Date()
}