Editing a QVariantMap from QML

问题

I have a QVariantMap created in C++ from a JSON object and I want to update this object from QML. I set it as a context property.

// main.cpp
engine.rootContext()->setContextProperty("myjson", myqvariantmap);

In QML I tried updating its properties but it seems to be read-only. The docs support this, saying

Mind that QVariantList and QVariantMap properties of C++ types are stored as values and cannot be changed in place by QML code. You can only replace the whole map or list, but not manipulate its contents.

Is there a workaround or an alternative type I can use in place of QVariatnMap?

回答1:

One possible option is QQmlPropertyMap:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlPropertyMap>
#include <QQmlContext>

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QQmlPropertyMap qpropertymap;
    qpropertymap.insert("name", "foo");

    QObject::connect(&qpropertymap, &QQmlPropertyMap::valueChanged, [](const QString &key, const QVariant &value){
        qDebug() << key << value;
    });

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty("qpropertymap", &qpropertymap);
    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);

    return app.exec();
}

import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")
    Component.onCompleted: {
        qpropertymap.name = "bar"
        // or
        // qpropertymap["name"] = "bar"
    }
}

回答2:

Here is a snippet to go with @eyllanesc's solution to convert from QVariantMap to QQmlPropertyMap.

void toPropertyMap(const QVariantMap& source, QQmlPropertyMap* dest) {
    for (const auto& key : source.keys()) {
        (*dest)[key] = source[key];
    }
}

来源：https://stackoverflow.com/questions/64879496/editing-a-qvariantmap-from-qml

标签

c++

qml