QT undefined reference compilation error on a signal - c++

Question

I am trying to add property title into the main window of my application. But when I try to compile it, the compiler gives me this error:
mainwindow.cpp:19: undefined reference to `MainWindow::titleChanged(QString const&)'
I tried it on mingw and msvc2013 both fails on the same line with this error. The header/source files:
mainwindow.h:
#ifndef MAINWINDOW
#define MAINWINDOW
#include <QObject>
#include <QString>
class MainWindow : public QObject {
QOBJECT_H
Q_PROPERTY(QString title READ getTitle WRITE setTitle NOTIFY titleChanged)
public:
MainWindow();
QString getTitle();
public slots:
void setTitle(const QString& title);
signals:
void titleChanged(const QString& title);
private:
QString title_;
};
#endif // MAINWINDOW
mainwindow.cpp:
#include "mainwindow.h"
#include <QString>
MainWindow::MainWindow()
{
}
QString MainWindow::getTitle()
{
return title_;
}
void MainWindow::setTitle(const QString& title)
{
if (title_ != title) {
title_ = title;
emit titleChanged(title);
}
}
If I add the method below to the end of mainwindow.cpp file, then the application compiles and runs, but the signal isn't emitted:
void MainWindow::titleChanged(const QString&)
{
}
I tried to cleaning out the project's build folders, it doesn't help :(. I am using QT 5.4 and working on QT Creator.

Answer 1

This question was already answered in comments by someone else. I just wanted to highlight the answer. The error in my case was in the header file
mainwindow.h:
class MainWindow : public QObject {
QOBJECT_H // This should be Q_OBJECT
...
I confused the QOBJECT_H macro used in QObject.h header file as an include guard with the Q_OBJECT macro used by QT's moc tool. Since the intellisense will offer you both options, they are easy to confuse.
I also got pointed to a good reading about common problems with signals/slots worth for reading: My signal / slot connection does not work