I've been trying to learn QtQuick for GUI creation, but I've been having a hard time understanding how to interact with QML objects from the C++ part of my test program.
Here's my simple QML file:
import QtQuick 2.2
import QtQuick.Window 2.1
Window {
id: mainWindow
visible: true
width: 800
height: 800
color: "#FFFF0000"
MouseArea {
anchors.fill: parent
onClicked: Qt.quit()
}
Rectangle {
id: testRect
width: 100
height: 100
anchors.centerIn: parent
color: "#FF0000FF"
}
}
Here's the basic C++ file that came with it (auto-generated by QtCreator):
#include <QGuiApplication>
#include <QQmlApplicationEngine>
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
return app.exec();
}
My issue is that I have no idea how to gain access to my 'Window' QML object, and as a result, I'm unable to alter any of its properties or the properties of its children! This part of the QtQuick documentation shows two methods of accessing QML objects from within C++ code, but neither of them seem to apply to this 'QQmlApplicationEngine' loading scheme.. I've also seen people use things like 'QApplicationViewer' and 'QDeclaritiveView', but I can't seem to find those in the official documentation at all..
I'm getting really frustrated with QtQuick; the 'simplicity' of QML seems to be lost in a sea of conflicting documentation and convoluted interface between C++ and QML. Is there anyway for me to access my QML objects while using the QQmlApplicationEngine method? I've tried using 'QuickView', but it doesn't seem to work well with Window QML objects..? Is QQmlApplicationEngine only useful for QML-only applications in a single file? So far, every piece of documentation and tutorial I've read has shown something different..
Any help or clarification would be appreciated. Ideally I'd like to know how to access and modify QML objects (like 'mainWindow', 'testRect', and other objects in other files) via my C++ code.
Turning my comment into a proper answer: this is usually done by two methods:
Get the root object of your QML scene through a view if you use QQuickView
or just the QQmlApplicationEngine
directly.
This next step can be omitted for root objects, but for "qml objects" in general, you will need to have the objectName property set and then you can find any children with the following method:
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QDebug>
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
// Step 1: get access to the root object
QObject *rootObject = engine.rootObjects().first();
QObject *qmlObject = rootObject->findChild<QObject*>("mainWindow");
// Step 2a: set or get the desired property value for the root object
rootObject->setProperty("visible", true);
qDebug() << rootObject->property("visible");
// Step 2b: set or get the desired property value for any qml object
qmlObject->setProperty("visible", true);
qDebug() << qmlObject->property("visible");
return app.exec();
}
See the documentation for property set and get in the official documentation:
bool QObject::setProperty(const char * name, const QVariant & value)
and
Good, we are now more or less done on the C++ side.
You will also need to have the objectName
property of your qml objects set if you wish to access more than just the root item as follows:
import QtQuick 2.2
import QtQuick.Window 2.1
Window {
id: mainWindow
objectName: "mainWindow"
...
}
This can be similarly done for any QML object. The key is "objectName" in here. You could omit that for the root object as the C++ side gets the root object directly, but since you are referring to QML objects in your question, I assume that you would like to solve it in general. Once you wish to do the same for any QML object, i.e. including children, you will need to use the objectName property.