qml parsing QVariant QJsonDocument to js object - qt

Question

A QVariant I took from C++ contains a QJsonDocument, and I want to convert it to a js object, but I only found the use of QJsonDocument in C++. I couldn't find how to use QJsonDocument in qml.
For Example:
Qml:
function qmlUpdateObject( Object ){
console.log(Object);
}
// console content: qml: QVariant(QJsonDocument, QJsonDocument({"appDesc":{"description":"SomeDescription","message":"SomeMessage"},"appName":{"description":"Home","imp":["awesome","best","good"],"message":"Welcome"}}))
// I want to get a js object: {"appDesc":{"description":"SomeDescription","message":"SomeMessage"},"appName":{"description":"Home","imp":["awesome","best","good"],"message":"Welcome"}}
C++:
QObject::connect( this, SIGNAL( updateData(QVariant)),
viewItem, SLOT( qmlUpdateObject(QVariant)) );
void Controller::setData(QString name)
{
QFile file("data.json");
QJsonDocument d = QJsonDocument::fromJson(file.readAll());
QByteArray dataJson = d.toJson(QJsonDocument::Compact);
emit updateData(dataJson);
}
UPDATE
Add this line and pass back, qml can successfully parse:
QByteArray dataJson = d.toJson(QJsonDocument::Compact);

Answer 1

There is no direct QJsonDocument conversion to a js object. One possible solution is to convert the QJsonDocument to QByteArray and export it to QML, and in QML do parse using JSON.parse():
C++
QByteArray dataJson = doc.toJson(QJsonDocument::Compact);
// send dataJson to QML
QML
var json = JSON.parse(dataJson)
Note:
It seems that the OP does not know the good practice of not accessing QML objects from C++ but must create a QObject and export it to QML.
The example provided by the OP is not necessary to use QJsonDocument since JSON.parse() does the same as QJsonDocument d = QJsonDocument::fromJson(file.readAll());.
#include <QFile>
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
class Controller: public QObject{
Q_OBJECT
public:
void setData(const QString & filename){
QFile file(filename);
if(file.open(QIODevice::ReadOnly))
Q_EMIT updateData(file.readAll());
}
Q_SIGNALS:
void updateData(const QByteArray & data);
};
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
Controller controller;
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("controller", &controller);
const QUrl url(QStringLiteral("qrc:/main.qml"));
QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
&app, [url](QObject *obj, const QUrl &objUrl) {
if (!obj && url == objUrl)
QCoreApplication::exit(-1);
}, Qt::QueuedConnection);
engine.load(url);
controller.setData("data.json");
return app.exec();
}
#include "main.moc"
import QtQuick 2.14
import QtQuick.Window 2.14
Window {
visible: true
width: 640
height: 480
title: qsTr("Hello World")
function qmlUpdateObject( data ){
var obj = JSON.parse(data)
console.log(obj);
}
Connections{
target: controller
onUpdateData: qmlUpdateObject(data)
}
}