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  1. Qt
  2. QTBUG-118847

cpp object property getter is called too often for local qml var access

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    Description

      We run into a weird issue when access a qml local var that assigned from cpp object property, the cpp object property method is called whenever the local var is accessed.

      The code should explain the issue more clearly:

      class MySingleton : public QObject
{
    Q_OBJECT
    QML_ELEMENT
    QML_SINGLETON
    Q_PROPERTY(QStringList mark READ mark NOTIFY markChanged)

public:
    explicit MySingleton(QObject* parent = nullptr) : QObject(parent) {}

    QStringList mark()
    {
        qDebug() << "** mark is called";
        return { "mark" };
    }

signals:
    void markChanged();
};

      // Some comments here
function example()
{
    var p = MySingleton.mark;
    if (p.length > 0) print(p);
}

      the output is:

      ** mark is called
** mark is called
[mark]

      that every time p is accessed, the MySingleton::mark() method is called; this only happen to QList return type, primitive return type does not have this issue.

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          relates to

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-127322 JSON.stringify() on property of type QVariantList reads property for every list element

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Reported

          Bug - A problem which impairs or prevents the functions of the product. QTBUG-81231 QJSEngine and QStringList properties handling, a potential performance issue

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed

          Task - A task that needs to be done. QTBUG-128358 Reduce unnecessary detaches and copies when handling value types and lists

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Reported
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              qtqmlteam Qt Qml Team User
              steve.k.chiu Steve K. Chiu
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              5 Start watching this issue

              Dates

                Created:
                Updated:

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