Unknown type name QML_ELEMENT

Question

In the new Qt 5.15.0 there is a new declarative way to register C++ types for usage in QML. I followed the steps given in Qt Help (https://doc.qt.io/qt-5/qtqml-cppintegration-definetypes.html#registering-an-instantiable-object-type) but it givens to me the following error:

/.../randomnumbergenerator.h:10: error: ‘QML_ELEMENT’ does not name a type
     QML_ELEMENT
     ^~~~~~~~~~~

The class's definition is, for the moment:

#ifndef RANDOMNUMBERGENERATOR_H
#define RANDOMNUMBERGENERATOR_H

#include <QObject>
#include <QRandomGenerator>

class RandomNumberGenerator : public QObject
{
    Q_OBJECT
    QML_ELEMENT
    QML_SINGLETON

public:
    explicit RandomNumberGenerator(QObject *parent = nullptr);

signals:

};

#endif // RANDOMNUMBERGENERATOR_H

EDIT: I already added to the .pro file the following:

CONFIG += c++11 qmltypes
QML_IMPORT_NAME = SimpleRng
QML_IMPORT_MAJOR_VERSION = 1

Answer 1

As they point out in the Qt forum you have to include <qml.h> (or <QtQml>)

Answer 2

The preconditions section of the documentation you quoted states that

All the macros mentioned below are available from the qqml.h header. You need to add the following code to the files using them in order to make the macros available:

#include <QtQml/qqml.h>

That seems to be the canonical answer and may avoid the issues that @lateus mentioned in comments.