Unhandled exception (access violation) when attempting to expose C++ type to QML

TLDR

Hi, I'm attempting to follow the tutorial here: http://doc.qt.io/qt-5/qtqml-cppintegration-exposecppattributes.html

The tutorial creates a C++ "Message" object and uses it in a QML project. Everything builds and links just fine (and MOC is run, as would be needed), but attempting to run it leads to a Unhandled exception which the stack trace says happens within app.exec(). Anyone have any pointers?

Unhandled exception at 0x00007FFC9106CD34 (Qt5Guid.dll) in testapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Exception thrown at 0x00007FFC9106CD34 (Qt5Guid.dll) in testapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Unhandled exception at 0x00007FFC9106CD34 (Qt5Guid.dll) in testapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Exception thrown at 0x00007FFC9106CD34 (Qt5Guid.dll) in testapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Unhandled exception at 0x00007FFC9106CD34 (Qt5Guid.dll) in testapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Exception thrown at 0x00007FFC9106CD34 (Qt5Guid.dll) in testapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Unhandled exception at 0x00007FFC9106CD34 (Qt5Guid.dll) in testapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Exception thrown at 0x00007FFC9106CD34 (Qt5Guid.dll) in testapp.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

I'm using Visual Studio 14 (2015) and Qt 5.6. Full source code below:

main.cpp:

#include "message.h"

#include <QtWidgets/QApplication>
#include <QtQml/QQmlContext>
#include <QtQml/QQmlEngine>
#include <QtQml/QQmlComponent>

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

    QQmlEngine engine;
    Message msg;
    engine.rootContext()->setContextProperty("msg", &msg);
    QQmlComponent component(&engine, QUrl::fromLocalFile("MyItem.qml"));
    component.create();

    return app.exec();
}

message.h:

#include <QtCore/QObject>

class Message : public QObject
{
    Q_OBJECT
	Q_PROPERTY(QString author READ author WRITE setAuthor NOTIFY authorChanged)
public:
    void setAuthor(const QString &a) {
	    if (a != m_author) {
		    m_author = a;
		    emit authorChanged();
	    }
    }
    QString author() const {
	    return m_author;
    }
signals:
    void authorChanged();
private:
    QString m_author;
};

MyItem.qml:

// MyItem.qml
import QtQuick 2.0

Text {
    width: 100; height: 100
    text: msg.author    // invokes Message::author() to get this value

    Component.onCompleted: {
        msg.author = "Jonah"  // invokes Message::setAuthor()
    }
}

(all of which are copied wholesale from the link at the top, with the exception of #include lines which aren't present in the tutorial).

SGaist

Hi and welcome to devnet,

That's a bug in the documentation (fix underway)
Change the body of main for:

QGuiApplication app(argc, argv);

QQuickView view;
Message msg;
view.engine()->rootContext()->setContextProperty("msg", &msg);
view.setSource(QUrl::fromLocalFile("MyItem.qml"));
view.show();

return app.exec();

TLDR

Awesome, thank you. This works just as you said it would:

#include "message.h"

#include <QtGui/QGuiApplication>
#include <QtQuick/QQuickView>
#include <QtQml/QQmlContext>
#include <QtQml/QQmlEngine>
#include <QtQml/QQmlComponent>

int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);

QQuickView view;
Message msg;
view.engine()->rootContext()->setContextProperty("msg", &msg);
view.setSource(QUrl::fromLocalFile("MyItem.qml"));
view.show();

return app.exec();

}