QTimer长时间超时

Question

Qt 5.7 32-bit on windows 10 64-bit long period timer

the interval of a QTimer is given in msecs as a signed integer, so the maximum interval which can be set is a little bit more than 24 days (2^31 / (1000*3600*24) = 24.85) I need a timer with intervals going far beyond this limit. So my question is, which alternative do you recommend? std::chrono (C++11) seems not to be suitable as it does not have an event handler?

Alain

Answer 1

You could always create your own class which uses multiple QTimer's for the duration they are valid and just count how many have elapsed.

Pretty simple problem. If you can only count to 10 and you need to count to 100 - just count to 10 ten times.

Answer 2

I would implement this in the following way:

Upon timer start, note the current time in milliseconds like this:

m_timerStartTime = QDateTime::currentMSecsSinceEpoch()

The, I would start a timer at some large interval, such as 10 hours, and attach a handler function to the timer that simply compared the time since it started to see if we are due:

 if(QDateTime::currentMSecsSinceEpoch() - m_timerStartTime > WANTED_DELAY_TIME){
      // Execute the timer payload
      // Stop interval timer
 }

This simple approach could be improved in several ways. For example, to keep the timer running even if application is stopped/restarted, simply save the timer start time in a setting or other persistent storage, and read it back in at application start up.

And to improve precision, simply change the interval from the timer handler function in the last iteration so that it tracks the initial end time perfectly (instead of overshooting by up to 10 minutes).