How to create a qml object from a qt c++ class [duplicate] - qt

Question

This question already has answers here:
Qt5. Embed QWidget object in QML
(5 answers)
Closed 5 years ago.
For a while I thought that I was not able to use Qt c++ classes with qml applications, but I found this: http://doc.qt.io/qt-5/qtqml-cppintegration-definetypes.html.
Now I'm trying to create an instantiable object type. I first ran into "Qwidget: Cannot create a Qwidget without QApplication" reading online it the answer seem to be just to change QGuiApplication to QApplication, but then I get: "ASSERT: "
!d->isWidget"
This is the Qt class that I'm trying to use as a qml type: http://doc.qt.io/qt-5/qlcdnumber.html.
Here is my main.cpp:
#include <QApplication>
#include <QQmlApplicationEngine>
#include <QLCDNumber>
#include <QQuickStyle>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QQmlApplicationEngine engine;
qmlRegisterType<QLCDNumber>("LCDNumber",1,0,"LCDNumber");
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
}
Here is what I'm trying to create in main.qml:
...
import LCDNumber 1.0
Window {
...
LCDNumber{
digitCount: 3
intValue: 1
mode: LCDNumber.Dec
segmentStyle: LCDNumber.Flat
smallDecimalPoint: false
value: 0
}
}
Is it really possible to create a qt c++ class in qml? I'm missing something?

Answer 1

Yes, it's possible!
In your class use the Tags Q_PROPERTY and Q_INVOKABLE to provide into QML access to properties and methods class, like this:
class NameYourClass : public QDeclarativeItem {
Q_OBJECT
Q_PROPERTY(int intProperty1 READ getIntProperty1 WRITE setIntProperty1)
Q_PROPERTY(QString strProperty2 READ getStrProperty2 WRITE setStrProperty2)
private:
int intProperty1;
QString strProperty2;
public:
explicit NameYourClass(QDeclarativeItem *parent = 0);
~NameYourClass();
Q_INVOKABLE int getIntProperty1() const;
Q_INVOKABLE void setIntProperty1(int value);
Q_INVOKABLE QString getStrProperty2() const;
Q_INVOKABLE void setStrProperty2(const QString &value);
}
Your main.cpp:
int main(int argc, char *argv[]) {
QApplication app(argc, argv);
qmlRegisterType<NameYourClass>("IdentifierName", 1, 0, "NameYourClass");
return app.exec();
}
Your QML file:
import IdentifierName 1.0
Rectangle {
id: nameRectangle
width: 999
height: 999
onSomethingChange: {
execFunction();
}
property NameYourClass nameDesired: nameObject
NameYourClass {
id: nameObject
intProperty1: 999
}
function execFunction() {
var varExample;
varExample = nameDesired.getIntProperty1();
nameDesired.setIntProperty1(varExample);
}
}
I do not think I've forgotten anything.
I hope it helps!