How to kill a timer

[Driftwood]

I have this code:

QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(scrollKeeper()));
timer->start(80);

As you can see, it triggers scrollKeeper() function where the timer continues to run. And run and run and run. I need to be able to kill it in scrollKeeper(), but I can't seem to make that happen.

Is there a way to get the timer's ID so i can use killTimer(ID)? Or will that even work with timer->start()?

[JoeCFD]

if ( nullptr == timer ) {
    **** output error msg *****
}
else {
   if ( timer->isActive() )  
   {
       timer->stop(); 
   }
}

[Driftwood]

@JoeCFD

I tried that last night and crashed. I guess I have this wired up all wrong, even after reading the docs and viewing a few examples online.

I'll keep on it, though. Thanks for your input.

[JoeCFD]

@Driftwood run your code in debugger and you can easily find the problem. call stop() should not crash your app.

[JonB]

@Driftwood said in How to kill a timer:

I tried that last night and crashed

It would crash if timer == nullptr, or doesn't point to a valid instance for whatever reason. What is the scope of your QTimer *timer = new QTimer(this);, because that's the timer-> you will need, and it doesn't look like a class member variable?

[JoeCFD]

@JonB Good point! timer should be defined in the header.

[Driftwood]

@JonB

snippet of mainwindow.cpp

void MainWindow::scrollKeeper()
{
    ui->label_About->move(380, g_counter);
    g_counter -= 1;
    if (g_counter < 100) {
        timer->stop();
        return;
    }
    if (g_counter < -(ui->label_About->height()))
        g_counter = ui->stackedWidget->height()+6;
//    qDebug()<< g_counter;
}


void MainWindow::on_action_About_triggered()
{
    ui->stackedWidget->setCurrentIndex(2);
    ui->label_About->move(380, ui->stackedWidget->height());

    g_counter = ui->stackedWidget->height()+6;
//    QTimer *timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(scrollKeeper()));
    timer->start(30);
}

snippet of the header file:

private:
    Ui::MainWindow *ui;

    int g_counter;

    QTimer *timer;

In the second function up there, it crashes at timer->start(30); with this error: QObject::connect: Cannot connect (null)::timeout() to MainWindow::scrollKeeper()

A for loop will work, if need be. And it's looking more and more that way =)

[JoeCFD]

@Driftwood
private:
Ui::MainWindow *m_ui{};
int m_gCounter{};
QTimer *m_timer{};

m_timer = new QTimer(this); ===>wrong: QTimer *timer = new QTimer(this);

[Driftwood]

@JoeCFD
Thank you. I see what I did wrong (more than one thing, really). It works nicely now. Before I decided I wanted the text to stop at a certain y axis, I had it scrolling nicely. I didn't realize the text skidding to a stop wld be so monumental to me.

But one last thing: Is there a way to get a timer's ID, or is that even necessary?

[JoeCFD]

@Driftwood timerId(); But what is for?

[Driftwood]

@JoeCFD

I was just curious about how to get a timer's ID. This is my first time to use QTimer. I read the docs and looked at a few examples and i still messed it up.

You've been a great help. Thanks again.

[mrjj]

@Driftwood

Hi
https://doc.qt.io/qt-5/qtimer.html#timerId