How to run code after some random/dynamic delay in Flutter?

Question

I would like to run a function with some random/dynamic delay. Future.delayed can help in this but it took time as const. I am unable to pass an expression or non const value as time. Is there any way to make it parameterise or random? So with each call delay will be different.

Future.delayed(const Duration(milliseconds: needRandomNumberHere), () {
    // code will be here
});

score 5 · Accepted Answer · answered Apr 17 '20 at 20:13

You can just use any variable, like others have shown here.

You are misunderstanding the const in this context.
There is no way to force const in Dart - it is always optional. You can only force yourself to use const by declaring it that way.

Future.delayed(Duration(milliseconds: 42), () {
    // code will be here
});
// does the exact same as:
Future.delayed(const Duration(milliseconds: 42), () {
    // code will be here
});

As you can tell, const is optional.

This means that the following will just work fine:

Future.delayed(Duration(milliseconds: Random().nextInt(420)), () {
    // code will be here
});

Yes, you are right. Once I remove `const` keyword its work. – Pankaj Anupam Apr 17 '20 at 20:18 — Pankaj Anupam, Apr 17 '20 at 20:18

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

1

Use Dart's Random class:

int nextInt(int max)

Generates a non-negative random integer uniformly distributed in the range from 0, inclusive, to max, exclusive.

So, in your code:

import 'dart:math';
Future.delayed(Duration(milliseconds: Random().nextInt(3000)), () {
    // code will be here
});

will run the code after a random time between 0 and 3000 milliseconds.

edited Jun 20 '20 at 09:12

Community

1
1

answered Apr 17 '20 at 17:25

Naslausky

3,443
1
14
24

score 1 · Answer 3 · answered Oct 16 '22 at 11:16

You can use it like this:

Timer? timer;
void startTimerRandomly() {
var random = Random();
var randomDuration = Duration(seconds: random.nextInt(10));
timer?.cancel();
timer=  Timer.periodic(
  randomDuration,
  (Timer timer) {
    if (mounted) {
       startTimerRandomly();
    } else {
      if (mounted) {
    
      }
    }
  },
);

}

score 0 · Answer 4 · answered Apr 17 '20 at 17:24

0

Please take a look at this to see how to generate random numbers in dart. What you can do is generate a random number and then pass it to the milliseconds field or even the seconds in the Duration.

answered Apr 17 '20 at 17:24

Abbas.M

3,086
3
11
22

Abba.m generating random number is not a issue. Actually, duration accept `const` only and random is not a `const`. – Pankaj Anupam Apr 17 '20 at 20:02
As clarified in the answer by creativecreatorormaybenot, the const is actually optional – Abbas.M Apr 17 '20 at 20:30

How to run code after some random/dynamic delay in Flutter?

4 Answers4