如何在Dart中运行重复功能? [英] How do I run a reoccurring function, in Dart?
问题描述
我想一遍又一遍地运行一个函数,但要间隔一段时间。如何使用Dart做到这一点?
您可以使用 Timer
类来安排单发和重复功能。
重复
这是运行重复功能的方式:
import'dart:async';
main(){
const oneSec = const Duration(seconds:1);
new Timer.periodic(oneSec,(Timer t)=> print(’hi!’));
}
Timer需要两个参数,一个持续时间和一个要运行的函数。持续时间必须是 Duration
的实例。回调必须使用单个参数,即计时器本身。
取消重复计时器
使用 timer.cancel()
取消重复计时器。这是计时器将计时器从重复计时器传递到回调运行的原因之一。
延迟后一次拍摄
要在延迟后安排一次功能(执行一次,以后再执行一次):
import'dart:async';
main(){
const 20.Millis = const持续时间(毫秒:20);
new Timer(twentyMillis,()=> print(’hi!’));
}
请注意,单次计时器的回调不带参数。 / p>
尽快拍摄
您还可以要求尽快运行某个函数,
import'dart:async';
main(){
Timer.run(()=> print(’hi!’));
}
在HTML中
计时器甚至可以HTML格式工作。实际上, window.setTimeout
已被删除,因此Timer是将来运行函数的唯一方法。
I'd like to run a function over and over, with a delay in between. How can I do this with Dart?
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 = const Duration(seconds:1);
new 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.
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 = const Duration(milliseconds:20);
new Timer(twentyMillis, () => print('hi!'));
}
Notice the callback for a one-shot timer does not take a parameter.
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!'));
}
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.
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