在QML中未调用C ++类型的析构函数

Question

I create a Sailfish app (using latest Sailfish SDK). I have a problem with exposing a C++ object to QML. It inherits QSettings,

class Settings : public QSettings
{
    Q_OBJECT
    /**/
public:
    explicit Settings() : QSettings("Marcin Mielniczuk", "BigText") {}
    ~Settings() { qDebug() << "Dying"; }

    /**/
};

I noticed that the destructor isn't called at all. (there's not destructor output)

I create the object like that:

import QtQuick 2.0
import Sailfish.Silica 1.0
import BigText 1.0
import "pages"

ApplicationWindow
{
    initialPage: MainPage { }
    Settings {id: settings}
}

My main.cpp is:

Q_DECL_EXPORT int main(int argc, char *argv[])
{
    QScopedPointer<QGuiApplication> app(Sailfish::createApplication(argc, argv));

    qmlRegisterType<Settings>("BigText", 1, 0, "Settings");

    QScopedPointer<QQuickView> view(Sailfish::createView("main.qml"));

    Sailfish::showView(view.data());

    return app->exec();
}

What am I doing wrong?

/edit: Text not being printed isn't an actual problem - it's just an indicator of the problem. The QSettings sycing in the destructor doesn't work too.

EDIT2: Please note, that ApplicationWindow in I'm using Sailfish Silica, not QtQuick.Controls, and the window is shown ok. These components must be a somewhat different to the stock qt quick components.

Answer 1

There's nothing inherently wrong with your logic. Here is a simplified version of it. I can run it locally, and consistently get a Dying message on output every time the window is closed and the application terminates.

If you cannot figure it out, I suggest transforming this code into what you're doing until it fails.

By the way, this is surely just a snippet of something larger you're doing, but at least as far as the example goes, these scoped pointers aren't doing much.

main.qml

import QtQuick 2.0
import BigText 1.0

Item {
    width: 300; height: 300
    Settings {id: settings}
}

main.cpp

class Settings : public QSettings
{
    Q_OBJECT
    public:
    Settings() : QSettings("Marcin Mielniczuk", "BigText") {}
    ~Settings() { qDebug() << "Dying"; }

};

int main(int argc, char *argv[])
{
    QScopedPointer<QGuiApplication> app(new QGuiApplication(argc, argv));
    qmlRegisterType<Settings>("BigText", 1, 0, "Settings");
    QScopedPointer<QQuickView> view(new QQuickView());
    view->setSource(QUrl::fromLocalFile("main.qml"));
    view->show();
    return app->exec();
}

Answer 2

您可以尝试放置和浏览ApplicationWindow并在某个时候显式使用destroy（）方法，看看会发生什么。

Answer 3

You cannot use QQuickView with an ApplicationWindow class. Not only is your destructor not called, your constructor isn't either , because the loading doesn't ever succeed.

The code below works fine under Qt 5.1.1. Tested on both OS X 10.8 and Windows 7.

main.qrc

<RCC>
  <qresource prefix="/">
    <file>main.qml</file>
  </qresource>
</RCC>

main.pro

QT       += core gui qml quick
TARGET = qml-appwin-end-18597527
TEMPLATE = app
SOURCES += main.cpp
OTHER_FILES += main.qml
RESOURCES += main.qrc

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QSettings>
#include <QQuickWindow>
#include <QtQml>
#include <QDebug>

class Settings : public QSettings
{
    Q_OBJECT
    public:
    Settings() : QSettings("Marcin Mielniczuk", "BigText") {}
    ~Settings() { qDebug() << "Dying"; }
};

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;
    qmlRegisterType<Settings>("BigText", 1, 0, "Settings");
    engine.load(QUrl("qrc:/main.qml"));
    QObject *topLevel = engine.rootObjects().value(0);
    QQuickWindow *window = qobject_cast<QQuickWindow *>(topLevel);
    window->show();
    return app.exec();
}

#include "main.moc"

main.qml

import QtQuick 2.0
import QtQuick.Controls 1.0
import BigText 1.0

ApplicationWindow {
    width: 300; height: 300
    Settings {id: settings}
}

Answer 4

Nothing is wrong with my code. It's something with the SDK. Debugging shows

ASSERT: "QThread::currentThread() == QCoreApplication::instance()->thread()" in file debugger/qqmldebugserver.cpp, line 576

Then the program is aborted and therefore destructor not called.