C++ class wouldn't build in bare bone QML application

[xalam]

I have a simple bare bone QML application and I just want to add a c++ class and use it from QML but I get error and it wouldn't even build. Here is the code.

@#include <QGuiApplication>
#include <QQmlApplicationEngine>

#include "mymodel.h"

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

MyModel model;

QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

// engine.rootContext()->setContextProperty("_MyModel", &model);

return app.exec();

}@

And the class MyModel is:

@#ifndef MYMODEL_H
#define MYMODEL_H

#include <QObject>

class MyModel : public QObject
{
Q_OBJECT
public:
explicit MyModel(QObject *parent = 0);

signals:

public slots:

};

#endif // MYMODEL_H@

the .cpp file of the class

@#include "mymodel.h"

MyModel::MyModel(QObject *parent) :
QObject(parent)
{
}
@

When I build, I get the following error:

@
main.obj:-1: error: LNK2019: unresolved external symbol "public: __thiscall MyModel::MyModel(class QObject *)" (??0MyModel@@QAE@PAVQObject@@@Z) referenced in function _main
debug\QMLCalc1.exe:-1: error: LNK1120: 1 unresolved externals
@

What is possibly wrong? I can't even get to the setContextProperty() call yet.

[andreyc]

Have included mymodel.cpp into the project?

[p3c0]

Also, unrelated to above error, use setContextProperty before loading the QML or else there would be some Reference Errors.

[xalam]

I had to 'Run QMake' from build menu which fixed it and project now builds fine without making any other change but I still don't uderstand why do I have to do that! It is a simple new project and I just added a class. Could anyone tell me what does QMake do? Can I add this as a step to build process? Thanks.

[dheerendra]

It generates the makes files again to compile your sources. You have added new class files to your project. So pro file got updated. I have seen some times it does not generate make file on its own after adding new class files. I have seen this more with when I'm using the qmake/qt creator with VC++. In general it is good practice to re-run the qmake once the pro-file is updated.