I became crazy about LNK2001 error.. in very small qml test...

filipdns

hello,

I'm trying to use example from qt doc and I receive an error that I don't understand where is the problem...

main.cpp

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

class ApplicationData : public QObject
{
    Q_OBJECT
public:
    Q_INVOKABLE QDateTime getCurrentDateTime() const {
        return QDateTime::currentDateTime();
    }
};

int main(int argc, char *argv[]) {
    
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    
    ApplicationData data;
    engine.rootContext()->setContextProperty("applicationData", &data);
    
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

main.qml

import QtQuick 2.9
import QtQuick.Window 2.2

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    Text { text: applicationData.getCurrentDateTime() }
}

context.pro

QT += quick qml
CONFIG += c++11

# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
        main.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

HEADERS +=

I received 3 error:

main.obj:-1: erreur : LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __thiscall ApplicationData::metaObject(void)const " (?metaObject@ApplicationData@@UBEPBUQMetaObject@@XZ)

main.obj:-1: erreur : LNK2001: unresolved external symbol "public: virtual void * __thiscall ApplicationData::qt_metacast(char const *)" (?qt_metacast@ApplicationData@@UAEPAXPBD@Z)

main.obj:-1: erreur : LNK2001: unresolved external symbol "public: virtual int __thiscall ApplicationData::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@ApplicationData@@UAEHW4Call@QMetaObject@@HPAPAX@Z)

What I did:

Delete builded folder
qmake
run
same problem...

clean project
qmake
run
same problem

When I remove
Q_OBJECT

no error but nothing on qml page off course...

Do you have an idea why I got this?...

Thank you for your help

Diracsbracket

@filipdns
Put the QObject -derived class using the Q_OBJECT macro into a header file such that the MOC can find it and process it.
http://doc.qt.io/qt-5/moc.html

#ifndef APPLICATIONDATA_H
#define APPLICATIONDATA_H

#include <QObject>
#include <QDateTime>

class ApplicationData : public QObject
{
    Q_OBJECT

public:
    Q_INVOKABLE QDateTime getCurrentDateTime() const {
        return QDateTime::currentDateTime();
    }
};

#endif // APPLICATIONDATA_H

I agree that the example in
http://doc.qt.io/qt-5/qtqml-cppintegration-contextproperties.html#setting-an-object-as-a-context-property
does not make this clear and is highly confusing.

filipdns

@Diracsbracket Great, thanks a lot!! I'm too stupid to didn't think that way before ;-)