How I change a property of a qml object from a cpp file?

NerdTronik

Im using Qt Quick Controls 2 and Im a completly inexpert qith qml

and Im stocked here:
*.h file:

#ifndef START_H
#define START_H

#include <QObject>
#include <QString>

class Image : public QObject {
  Q_OBJECT
  Q_PROPERTY(QString source READ source WRITE setSource NOTIFY sourceChanged)
public:
  explicit Image(QObject *parent = nullptr);

  QString source();
  void setSource(const QString &source);

signals:
  void sourceChanged();

protected:
  QString m_source = "648115.jpg";
};

#endif // START_H

*.cpp file:

#include "start.h"

Image::Image(QObject *parent) : QObject(parent) {}
QString Image::source() { return m_source; }

void Image::setSource(const QString &source) {
  if (source == m_source)
    return;
  m_source = source;
  emit sourceChanged();
}

*.qml file:

import PTrans.class.Imagen 1.0
Image {
        id: backg
        anchors.fill: parent
        fillMode: Image.PreserveAspectCrop
        onActiveFocusChanged: backg.source=Imagen.source

    }

main.cpp file:

#include <QtQml/QQmlProperty>
#include <QQuickWindow>
#include <QTime>
#include <QString>

int main(int argc, char *argv[])
{
  QTime time=QTime::currentTime();
  QDate date=QDate::currentDate();
  QString day=date.toString("ddd, dd of mmm of yyyy");
  QString hour=time.toString("h:m:s ap");

  QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

  QGuiApplication app(argc, argv);
  QQmlApplicationEngine engine;
  engine.load(QUrl(QStringLiteral("qrc:/start.qml")));
  qmlRegisterType<Image>("PTrans.class.Imagen", 1, 0, "Imagen");

  QQuickWindow *backg = (QQuickWindow *)engine.rootObjects().first();
  if (backg)
  backg->setProperty("source","2.jpg");
  if (engine.rootObjects().isEmpty())
    return -1;
  return app.exec();

}

dheerendra

Why do you want to change the property of QML object from c++ ? We can help you based on this. It is not a good practice to change property of QML object from C++. There are ways to do it. Not advisable.

NerdTronik

The thing is that I need to process all the data trough c++ and qml is just for the visual of the program, for example: read a c++ variable and put it data in a label on qml. I know that its harder than the normal way, but my teacher wants it that way.

mrjj

@NerdTronik
Hi
Having c++ do the heavy lifting and use QML as GUI is a good concept and
also very normal.
However, you should not directly try to access the QML Objects from c++ but rather
make the c++ data available to QML.
http://doc.qt.io/qt-5/qtqml-cppintegration-topic.html