How to access a nested QML object from C++?

[TheIndependentAquarius]

Here is a reproducible example:

main.qml

import QtQuick 2.0
 
Item {
    id : root
    width: 360
    height: 360
 
    Text {
        id : t1
        text: qsTr("Hello World")
        property int someNumber: 1000
        anchors.centerIn: parent
    }
    MouseArea {
        anchors.fill: parent
        onClicked: {
            Qt.quit();
        }
    }
}

import QtQuick 2.0

Item {
    id : root
    width: 360
    height: 360

    Text {
        id : t1
        text: qsTr("Hello World")
        property int someNumber: 1000
        anchors.centerIn: parent
    }
    MouseArea {
        anchors.fill: parent
        onClicked: {
            Qt.quit();
        }
    }
}

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main.cpp

#include <QtGui/QGuiApplication>
#include <QQmlEngine>
#include <QQmlComponent>
#include <QQmlProperty>
#include <QDebug>
 
#include "qtquick2applicationviewer.h"
 
int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
 
    QtQuick2ApplicationViewer viewer;
    viewer.setMainQmlFile(QStringLiteral("qml/untitled/main.qml"));
    viewer.showExpanded();
 
    QQmlEngine engine;
    QQmlComponent component(&engine, "qml/untitled/main.qml");
    QObject *object = component.create();
 
    qDebug() << "Property value:" << QQmlProperty::read(object, "root.ti.someNumber").toInt();
 
    return app.exec();
}

#include <QtGui/QGuiApplication>
#include <QQmlEngine>
#include <QQmlComponent>
#include <QQmlProperty>
#include <QDebug>

#include "qtquick2applicationviewer.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QtQuick2ApplicationViewer viewer;
    viewer.setMainQmlFile(QStringLiteral("qml/untitled/main.qml"));
    viewer.showExpanded();

    QQmlEngine engine;
    QQmlComponent component(&engine, "qml/untitled/main.qml");
    QObject *object = component.create();

    qDebug() << "Property value:" << QQmlProperty::read(object, "root.ti.someNumber").toInt();

    return app.exec();
}

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I wish to access the property somenumber of the text of the QML Item. The above method isn't producing the desired result.

How to do it?

[anda_skoa]

QQmlProperty::read() needs the object from which to read the property. So you need to find the Text element.
You can set the objectName property on the Text element and then use QObject::findChild on the object you have.

However, I would strongly advise to reconsider doing that at all. Accessing QML generated objects from C++ like that tightly couples the C++ code to the QML code, which is usually the very opposite of what one would want.

What is the goal you are trying to reach?

Cheers,
_

[d_stranz]

However, I would strongly advise to reconsider doing that at all. Accessing QML generated objects from C++ like that tightly couples the C++ code to the QML code, which is usually the very opposite of what one would want.

Agreed. I think the preferred way to do this is the same way you would make a C++ class - hide the implementation details behind public methods that do what you need behind the scenes. Users of the public UI don't need to know anything about what happens inside the class.

In the QML case, you can declare functions inside your top-level Item that reach down into the QML hierarchy to get, set, or do something. Outside the QML, the user only knows that there is some function that can retrieve a number from somewhere. This enables you to loosely couple the C++ and QML. Another alternative is to use signals and slots to talk between the two layers.

import QtQuick 2.0
 
    Item {
      id : root
      width: 360
      height: 360
 
      function getSomeNumber() {
         return t1.someNumber
      }
 
      function setSomeNumber( int number ) {
         t1.someNumber = number
      }
 
      Text {
        id : t1
        text: qsTr("Hello World")
        property int someNumber: 1000
        anchors.centerIn: parent
      }
      MouseArea {
        anchors.fill: parent
        onClicked: {
        Qt.quit();
        }
      }
   }

import QtQuick 2.0
     
    Item {
      id : root
      width: 360
      height: 360
     
      function getSomeNumber() {
         return t1.someNumber
      }

      function setSomeNumber( int number ) {
         t1.someNumber = number
      }

      Text {
        id : t1
        text: qsTr("Hello World")
        property int someNumber: 1000
        anchors.centerIn: parent
      }
      MouseArea {
        anchors.fill: parent
        onClicked: {
        Qt.quit();
        }
      }
   }

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[anda_skoa]

In the QML case, you can declare functions inside your top-level Item that reach down into the QML hierarchy to get, set, or do something. Outside the QML, the user only knows that there is some function that can retrieve a number from somewhere. This enables you to loosely couple the C++ and QML. Another alternative is to use signals and slots to talk between the two layers.

Or a propery on the C++ side that you simply bind to in QML.

Cheers,
_