Interaction with qml objects from C++ code - c++

Question

I am trying to interact with an qml object from C++ file using QtQuick. But unfortunatelly unsuccessfully for now. Any idea what Im doing wrong? I tried 2 ways how to do it, result of the first was that findChild() returned nullptr, and in second try I am getting Qml comnponent is not ready error. What is the proper way to do it?
main:
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QLatin1String("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
// 1-st attempt how to do it - Nothing Found
QObject *object = engine.rootObjects()[0];
QObject *mrect = object->findChild<QObject*>("mrect");
if (mrect)
qDebug("found");
else
qDebug("Nothing found");
//2-nd attempt - QQmlComponent: Component is not ready
QQmlComponent component(&engine, "Page1Form.ui.qml");
QObject *object2 = component.create();
qDebug() << "Property value:" << QQmlProperty::read(object, "mwidth").toInt();
return app.exec();
}
main.qml
import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3
ApplicationWindow {
visible: true
width: 640
height: 480
Page1 {
}
Page {
}
}
}
Page1.qml:
import QtQuick 2.7
Page1Form {
...
}
Page1.Form.ui.qml
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3
Item {
property alias mrect: mrect
property alias mwidth: mrect.width
Rectangle
{
id: mrect
x: 10
y: 20
height: 10
width: 10
}
}

Answer 1

findChild takes object name as first parameter. But not ID.
http://doc.qt.io/qt-5/qobject.html#findChild.
Here in your code, you are trying to query with id mrect. So it may not work.
Add objectName in your QML and then try accessing with findChild using object name.
Something like below (I did not try it. So chances of compile time errors):
Add objectName in QML
Rectangle
{
id: mrect
objectName: "mRectangle"
x: 10
y: 20
height: 10
width: 10
}
And then your findChild as shown below
QObject *mrect = object->findChild<QObject*>("mRectangle");