How do I run a reoccurring function, in Dart?

Question

I'd like to run a function over and over, with a delay in between. How can I do this with Dart?

Answer 1

You can use the Timer class to schedule one-shot and repeating functions.

Repeating

Here is how you run a repeating function:

import 'dart:async';
main() {
  const oneSec = Duration(seconds:1);
  Timer.periodic(oneSec, (Timer t) => print('hi!'));
}

The Timer takes two arguments, a duration and a function to run. The duration must be an instance of Duration. The callback must take a single parameter, the timer itself.

Canceling a repeating timer

Use timer.cancel() to cancel a repeating timer. This is one reason why timer is passed to the callback run from a repeating timer.

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One-shot after a delay

To schedule a one-shot function after a delay (execute once, some time in the future):

import 'dart:async';
main() {
  const twentyMillis = Duration(milliseconds:20);
  Timer(twentyMillis, () => print('hi!'));
}

Notice the callback for a one-shot timer does not take a parameter.

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One-shot as soon as possible

You can also request that a function is run as soon as possible, at least one event-loop tick in the future.

import 'dart:async';
main() {
  Timer.run(() => print('hi!'));
}

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In HTML

Timers even work in HTML. In fact, window.setTimeout was removed, so Timer is the only way to run a function in the future.