c++ - LNK2019 unresolved External Symbol for a QObject

I'm getting the following errors when building with QMake:

• LNK2019: unresolved external symbol "public: void __cdecl TimerTodo::notify(class TodoBaseTask *)" (?notify@TimerTodo@@QEAAXPEAVTodoBaseTask@@@Z) referenced in function "private: void __cdecl TimerTodo::timerOver(void)" (?timerOver@TimerTodo@@AEAAXXZ)




• LNK2019: unresolved external symbol "public: void __cdecl TimerTodo::hasNotified(class TimerTodo *)" (?hasNotified@TimerTodo@@QEAAXPEAV1@@Z) referenced in function "private: void __cdecl TimerTodo::timerOver(void)" (?timerOver@TimerTodo@@AEAAXXZ)




• LNK1120: 2 unresolved externals

This is my header:

#ifndef TIMERTODO_H
#define TIMERTODO_H


#include 

class TodoBaseTask;

class TimerTodo : public QTimer
{
public:
    TimerTodo(TodoBaseTask *timer);
    void StartTimer();

private slots:
    void timerOver();
signals:
    void notify(TodoBaseTask *todo);
    void hasNotified(TimerTodo *timer);
private:
    TodoBaseTask *m_todo;
};

#endif // TIMERTODO_H

And this is my source:

#include "timertodo.h"
#include "todobasetask.h"

TimerTodo::TimerTodo(TodoBaseTask *todo)
{
    m_todo = todo;

    connect(this, SIGNAL(timeout()), this, SLOT(timerOver()));
}

void TimerTodo::StartTimer()
{
    QDateTime nextNotify = m_todo->getDeadLine().addDays(-1);
    this->start(QDateTime::currentDateTime().msecsTo(nextNotify));
}

void TimerTodo::timerOver()

{
    emit notify(m_todo);
    emit hasNotified(this);
}

How to fix it?

Answer

This is explained in Qt documentation:

The moc tool reads a C++ header file. If it finds one or more class declarations that contain the Q_OBJECT macro, it produces a C++ source file containing the meta-object code for those classes. Among other things, meta-object code is required for the signals and slots mechanism, the run-time type information, and the dynamic property system.

(emphasis mine)

So you need to put this macro in every class that has its own signals or slots.