How to create some Timers at run time and handle them?

[Christian Ehrlicher]

@Jamshid said in How to create some Timers at run time and handle them?:

So using QTimer with specific slots won't work.

There is always QObject::sender() where you can see where the signal is coming from. Apart from this why not storing all created timers in a QVector/QHash/whatever so you can access them later on?

[Jamshid]

@artwaw I'm new to Qt but I'll try it. Thanks.

[Jamshid]

@Christian-Ehrlicher I'm trying sender(), I can store created timers in a vector and connect all created timers' timeout signal to one slot, my problem is this how to determine in that slot which timer timed out. I think QObject::sender() will help. let me try it.

[J.Hilk]

@Jamshid I would actually suggest to use a lambda over the sender() approach

for(int i(0); i <10; i++){
        QTimer *t = new QTimer(this);
        connect(t, &QTimer::timeout, this, [=]()->void{timerSlot(i);});
        m_timers.append(t);
   }

...
public slots:
    void timerSlot(int timeId);

[JonB]

@Jamshid
For a slot function sender should give you which timer. My understanding (untested!) is that if you use a lambda you do not get a sender. But then @J-Hilk is, I think, offering a lambda which passes the timerId as a parameter for you. Both sound like they would work.

[J.Hilk]

@JonB well, yes, we originally talked about identifying the timer that called the slot, what better way than an int ? 😉

Well, If one is more interested in the Timer Object....

for(int i(0); i <10; i++){
        QTimer *t = new QTimer(this);
        connect(t, &QTimer::timeout, this, [=]()->void{timerSlot(t);});
        m_timers.append(t);
   }

...
public slots:
    void timerSlot(QTimer *timer);

[Jamshid]

@J-Hilk I test this code, It only passes the last timer ID.

if (!List.contains(str))
{
// Start timer
timer = new QTimer(this);
timer->setInterval(200);
timer->start();
connect(timer, &QTimer::timeout, this, [=]()->void{integrityTimersEvent(timer->timerId());});

//
timersList.append(timer);
timersIDList.append(timer->timerId());
}

---

void FrameProcessor::integrityTimersEvent(int timerID)
{
    qDebug() << "integrityTimersEvent => Timer ID:" << timerID;
}

Am I doing it right way?

[JonB]

@Jamshid , @J-Hilk

It only passes the last timer ID.

This is just the kind of behaviour I found when playing with lambdas (which is why I don't much like them, let's not go there)! To get it right, I believe, you must pass the timer->timerID(), or the whole timer, as a parameter to the lambda. Not sure of the C++ (I'm Python) syntax, but I think it must go inside the () you have...

EDIT Oh well, since @J-Hilk shows it works below, I must be mistaken, sorry.... I had this kind of problem with Python lambdas, they must not directly access a changing value in the caller in their body code, instead the caller must pass that as a parameter....

[J.Hilk]

@Jamshid
should work fine,

take a look at the example I made:

int MainWindow::count = 0;
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    for(int i(0); i <10; i++){
        QTimer *t = new QTimer(this);
        connect(t, &QTimer::timeout, this, [=]()->void{timerSlot(t->timerId());});
        m_timers.append(t);
        t->start(100);
   }
}

void MainWindow::timerSlot(int timerId)
{
    qDebug() << timerId;
    qDebug() << Q_FUNC_INFO << count++;
}

which results in the correct call of:

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void MainWindow::timerSlot(int) 0
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---

edit: @JonB
the [=] is a "capture everything by copy" indicator. So no explicit capture of the id should be required

[Christian Ehrlicher]

@Jamshid said in How to create some Timers at run time and handle them?:

Am I doing it right way?

I would guess timer is a member variable, then yes you're doing it wrong. You copy the whole context ( [=]) and therefore the access inside the lambda is 'this->timer'

[J.Hilk]

@Jamshid
actually this

timer = new QTimer(this);
timer->setInterval(200);
timer->start();
connect(timer, &QTimer::timeout, this, [=]()->void{integrityTimersEvent(timer->timerId());});

is referencing the member variable

try the following:

QTimer *t = new QTimer(this);
t->setInterval(200);
t->start();
connect(t, &QTimer::timeout, this, [=]()->void{integrityTimersEvent(t->timerId());});
timer = t;

[Jamshid]

@J-Hilk Thanks a lot, now it works, I'm new to Qt and this topic I think was a little bit advanced for me :)

[Jamshid]

Thank you all dear friends, that’s really kind of you.
Your help is so appreciated.