Lets play a game... thermonuclear wa...sorry QDate to JS Date conversion!

Demolishun

So if I create a Date in QML JS. Say new Date(). Then I send this Date to a function that accepts QDate then it will have the correct date stored inside. However, if I take the same QDate and convert it to Date by returning a QDate in QML JS it will be off by one day.

I store a date in my database by converting the QDate to a string in format "yyyy/MM/dd". I can convert back to QDate easy using same format string. Then I see the JS Date loses a day when QDate to Date occurs.

So I have this terrible hack when I first read in this Date from database:

~~tdate.setDate(tdate.getDate()+1)~~ Don't use this approach. Use QDateTime instead of QDate.

I will submit a bug report to Qt, but I wanted to share my fix in case other people run into this. Kind of in shock this is a bug at all.

Qt 5.15.8 x86

JKSH

@Demolishun said in Lets play a game... thermonuclear wa...sorry QDate to JS Date conversion!:

Qt 5.15.8 x86

Which compiler?

I know of at least 1 case where JS Date issues are caused by an issue in the compiler: https://bugreports.qt.io/browse/QTBUG-95993

fcarney

Repeatable gcc 7.5.0 Qt 5.15.2 x86 :

main.qml:

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("QDate to Date bug")

    Component.onCompleted: {
        let date = new Date()
        console.log(date)
        dobj.setDate(date)

        let ndate = dobj.date()
        console.log(ndate)
    }
}

main.cpp:

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

#include <QDate>

class DateObject : public QObject
{
    Q_OBJECT
public:
    DateObject(QObject* parent=nullptr)
        : QObject(parent)
    {
    }

    QDate m_date;

    Q_INVOKABLE QDate date(){
        qDebug() << "date()" << m_date;
        return m_date;
    }

    Q_INVOKABLE void setDate(QDate ndate){
        qDebug() << "setDate()" << ndate;
        m_date = ndate;
    }
};

int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    auto context = engine.rootContext();
    DateObject dobj;
    context->setContextProperty("dobj", &dobj);

    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();
}

#include "main.moc"

result:

qml: Mon Feb 21 08:33:22 2022 GMT-0700
setDate() QDate("2022-02-21")
date() QDate("2022-02-21")
qml: Sun Feb 20 17:00:00 2022 GMT-0700

Demolishun

My approach was lossy. QDate loses time information. Changing data type for C++ to QDateTime keeps the time info even if I don't need that. The time zones have an affect. It seems JS Date can interchange between C++ QDate or QDateTime. QDateTime is the preferred and doesn't cause errors.