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Thread: How to start a QTimer in this situation?

  1. #1
    Join Date
    Sep 2020
    Qt products

    Question How to start a QTimer in this situation?

    Qt Code:
    1. class Foo {
    2. private:
    3. QTimer *timer = nullptr;
    5. public:
    6. void Foo (QTimer *timer) : timer(timer) { }
    8. void bar () {
    9. this->timer->start();
    10. }
    11. };
    13. ...
    15. QTimer *timer = new QTimer();
    16. Foo *foo = new foo(timer);
    18. obj.func(foo);
    19. timer->connect(timer, &QTimer::timeout, [] {
    20. // do something
    21. });
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    The program runs in the following order:
    1. a third party library creates a new thread.
    2. foo object is registered in the library through its obj::func() method.
    3. the library calls foo::bar() method.

    But after that, the program doesn't work with error message
    QObject::startTimer: Timers cannot be started from another thread.

    Could you give me some advice if you have a good idea? Thanks.
    Last edited by iaapmm; 28th September 2020 at 05:53.

  2. #2
    Join Date
    Mar 2009
    Brisbane, Australia
    Thanked 1,595 Times in 1,523 Posts
    Qt products
    Qt4 Qt5
    Unix/X11 Windows
    Wiki edits

    Default Re: How to start a QTimer in this situation?

    Try this...
    Give the Foo class a timeout() signal.
    Create the QTimer object inside Foo (pass in a period etc.): hopefully you end up with the timer in the same thread as the Foo object.
    Connect the timer's timeout() signal to Foo's timeout() signal. This will cause your foo object to emit timeout() when the internal timer emits timeout().

  3. The following user says thank you to ChrisW67 for this useful post:

    iaapmm (28th September 2020)

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