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

Question

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 1

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.

Answer 2

Here you can find a recursive method looking for a QML item by objectName and starting at QQmlApplicationEngine::rootObjects():
////
static QQuickItem* FindItemByName(QList<QObject*> nodes, const QString& name)
{
for(int i = 0; i < nodes.size(); i++){
// search for node
if (nodes.at(i) && nodes.at(i)->objectName() == name){
return dynamic_cast<QQuickItem*>(nodes.at(i));
}
// search in children
else if (nodes.at(i) && nodes.at(i)->children().size() > 0){
QQuickItem* item = FindItemByName(nodes.at(i)->children(), name);
if (item)
return item;
}
}
// not found
return NULL;
}
///
static QQuickItem* FindItemByName(QQmlApplicationEngine* engine, const QString& name)
{
return FindItemByName(engine->rootObjects(), name);
}

Answer 3

What is the use case for this? It might be better to just treat the [text, someNumber] struct or object as the model. Then you only need to find the model object. Or you could create the model object on the C++ side and set it in the QML context. You could access the model and its nested properties in QML:
Text {
text: model.text
property int someNumber: model.someNumber
}