QTimer, created earlier but started later, did not work - qt

Question

The code is in C++/Qt.
Basically, I wanted to create a timer (but not started) and started it later when necessary. But it did not work.
If I created and started the timer immediately, it worked as expected.
The idea of the code is like the followings:
mytimer.cpp:
#include "mytimer.h"
#include <QtCore>
MyTimer::MyTimer()
{
timer = new QTimer(this);
connect(timer,SIGNAL(timeout()),this,SLOT(mySlot()));
// timer->start(1000);
}
void MyTimer::mySlot()
{
qDebug()<<"timer executed";
}
MyTimer::startTimer(void)
{
timer->start(1000);
}
Note: startTimer() is triggered from another thread with an signal. I did debug the code and startTimer() function did get called as expected but the Timer did NOT start.
And in the main.cpp:
#include <QApplication>
#include "mytimer.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MyTimer mtimer;
qDebug()<<"DONE";
return a.exec();
}
I don't know why I could not start the timer later.

Answer 1

This is the main problem: "Note: startTimer() is triggered from another thread with an signal". However, you instantiate your MyTimer on the main thread which is different, since you try to start your timer on a different thread. You should either create your timer on the thread you want timeout to trigger or move your timer to that thread, and then connect your timer to timeout and slot. For instance, you could do like this maybe (not checked if it would really work):
MyTimer::startTimer(void)
{
timer->moveToThread(QThread::currentThread());
connect(timer, &QTimer::timeout, this, &MyTimer::mySlot);
timer->start(1000);
}
However, I would suggest the following approach, since moving objects between threads might mess up with your code, make it harder to manage, so the simpliest possible solution should be prefered to solve your problem, in my opinion.
MyTimer::startTimer(void)
{
// Create your timer on the thread you want
timer = new QTimer(this);
// Connect signal and slot
connect(timer, &QTimer::timeout, this, &MyTimer::mySlot);
// Start the timer
timer->start(1000);
}
Which one to use is up to you, but you should know that connecting signals and slots between different threads is not working under Qt, and all of the connections should be instantiated on the same thread, and actions triggering these connections should also be executed on the same thread where connection has been introduced.