CODEWITHSUNDEEP
c++multithreadingqtqtimer
Alex
Alex

Reputation: 371

start QTimer from another class

I have the following classes:

class MainWindow : public QMainWindow
{

public:
void StartTimer()
{
     timer = new QTimer(this);
     timer.start(100);

}

private:
QTimer *timer;

};


class AnotherClass
{

public:
MainWindow *window;
void runTimer()
{
    window->StartTimer();
}


};

Assuming the window pointer is correctly pointing to the mainwindow, if I try to call runTimer() , I receive this error:

QObject: Cannot create children for a parent that is in a different thread.
(Parent is MainWindow(0x7fff51ffe9f0), parent's thread is QThread(0x7fd1c8d001d0), current thread is QThread(0x7fd1c8f870c0)
QObject::startTimer: Timers can only be used with threads started with QThread

My guess for this error was that since runTimer was being called from a different thread it was also trying to initialize in that same thread? instead of the mainwindow thread?

If I initialize the timer in the default constructor of the main window I receive

QObject::startTimer: Timers cannot be started from another thread

How can I tell a QTimer to start from another class?

Upvotes: 0

Views: 975

Answers (1)

davepmiller
davepmiller

Reputation: 2708

You can use signals and slots.

class AnotherClass : public QObject
{

    Q_OBJECT

public:

    MainWindow * window;

    AnotherClass() : window( new MainWindow )
    {
        // Connect signal to slot (or just normal function, in this case )
        connect( this, &AnotherClass::signalStartTimer,
                 window, &MainWindow::StartTimer,
                 // This ensures thread safety, usually the default behavior, but it doesn't hurt to be explicit
                 Qt::QueuedConnection );

        runTimer();
    }

    void runTimer()
    {
        emit signalStartTimer();
    }

signals:

    void signalStartTimer();

};

Upvotes: 1

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