Expose QPointer returned from Q_INVOKABLE to QJSEngine

David Pinelo

Hi All,

Let's this code:

test.h:

#ifndef TEST_H
#define TEST_H

#include <QtCore>

class Test : public QObject {
    Q_OBJECT

public:

    Q_INVOKABLE Test(QObject *parent = Q_NULLPTR) : QObject(parent) {};

    Q_INVOKABLE QPointer<QObject> getMyQPointer()
    {
        QObject *o1 = new QObject(this);
        o1->setObjectName("O1");
        return o1;
    }

    Q_INVOKABLE QObject * getMyRawPointer()
    {
        QObject *o2 = new QObject(this);
        o2->setObjectName("O2");
        return o2;
    }
};

Q_DECLARE_METATYPE(Test)
Q_DECLARE_METATYPE(Test*)

#endif // TEST_H

main.cpp:

#include <QtCore>
#include <QtQml>
#include "test.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QJSEngine engine;
    engine.installExtensions(QJSEngine::AllExtensions);
    engine.globalObject().setProperty("TEST", engine.newQMetaObject(&Test::staticMetaObject));
    QJSValue r = engine.evaluate("var t = new TEST; var p = t.getMyQPointer(); var r = t.getMyRawPointer(); console.log('Object with QPointer: ' + p.objectName); console.log('Raw pointer: ' + r.objectName); console.log(p) ; console.log(r);");
        return 0;
}

Output is:

js: Object with QPointer: undefined  // <--- **Expected to be O1**
js: Raw pointer: O2
js: QVariant(QPointer<QObject>, QObject(0x5622e05f5010, name = "O1"))
js: QObject(0x5622e0595d10, "O2")

As you can see, output is different if you use QPointer o raw pointer. Is it possible to return QPointer through Q_INVOKABLE on a QJSEngine script and have same behaviour as raw pointer registered with Q_DECLARE_METATYPE?

Thanks!

sierdzio

@David-Pinelo I don't think so. And also, please remember that returning a QPointer is not necessary and not recommended:

A guarded pointer will automatically cast to a T *, so you can freely mix guarded and unguarded pointers. This means that if you have a QPointer<QWidget>, you can pass it to a function that requires a QWidget *. For this reason, it is of little value to declare functions to take a QPointer as a parameter; just use normal pointers. Use a QPointer when you are storing a pointer over time.

(https://doc.qt.io/qt-6/qpointer.html)