TheIndependentAquarius TheIndependentAquarius - 3 months ago 26
C++ Question

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

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();
}
}
}


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.t1.someNumber").toInt();

return app.exec();
}


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?

Answer

You have two ways (at least) to accomplish this depending on your personal preference.

QML code extension

You can add a property alias to the root item as follows:

import QtQuick 2.0

Item {
    id : root
    width: 360
    height: 360

    property alias mySomeNumber: t1.someNumber // This is the addition

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

C++ code extension

Since the QML items are QObject, you can look for the children explicitly as well, just as you would do it in a C++ QObject hierarchy. The code would be something like this:

#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();

    // This line is added

    QObject *childObject = object->findChild<QObject*>("SomeNumberText");

    // The following line is modified respectively

    qDebug() << "Property value:" << QQmlProperty::read(childObject, "someNumber").toInt();

    return app.exec();
}

However, this means you will need to add the objectName: "SomeNumberText" line to your Text child item in the qml file.