How do I generate random numbers in Dart?

Question

How do I generate random numbers using Dart?

Answer 1

try this, you can control the min/max value :

import 'dart:math';

void main(){
  random(min, max){
    var rn = new Random();
    return min + rn.nextInt(max - min);
  }
  print(random(5,20)); // Output : 19, 6, 15..
}

Answer 2

Let me solve this question with a practical example in the form of a simple dice rolling app that calls 1 of 6 dice face images randomly to the screen when tapped.

first declare a variable that generates random numbers (don't forget to import dart.math). Then declare a variable that parses the initial random number within constraints between 1 and 6 as an Integer.

Both variables are static private in order to be initialized once.This is is not a huge deal but would be good practice if you had to initialize a whole bunch of random numbers.

static var _random = new Random();
static var _diceface = _random.nextInt(6) +1 ;

Now create a Gesture detection widget with a ClipRRect as a child to return one of the six dice face images to the screen when tapped.

GestureDetector(
          onTap: () {
            setState(() {
              _diceface = _rnd.nextInt(6) +1 ;
            });
          },
          child: ClipRRect(
            clipBehavior: Clip.hardEdge,
            borderRadius: BorderRadius.circular(100.8),
              child: Image(
                image: AssetImage('images/diceface$_diceface.png'),
                fit: BoxFit.cover,
              ),
          )
        ),

A new random number is generated each time you tap the screen and that number is referenced to select which dice face image is chosen.

I hoped this example helped :)

Dice rolling app using random numbers in dart

Answer 3

Here's a snippet for generating a list of random numbers

import 'dart:math';

main() {
  var rng = new Random();
  var l = new List.generate(12, (_) => rng.nextInt(100));
}

This will generate a list of 12 integers from 0 to 99 (inclusive).

Answer 4

Just wrote this little class for generating Normal Random numbers... it was a decent starting point for the checking I need to do. (These sets will distribute on a "bell" shaped curve.) The seed will be set randomly, but if you want to be able to re-generate a set you can just pass some specific seed and the same set will generate.

Have fun...

class RandomNormal {
  num     _min, _max,  _sum;
  int     _nEle, _seed, _hLim;
  Random  _random;
  List    _rNAr;

  //getter
  List get randomNumberAr => _rNAr;

  num _randomN() {
    int r0 = _random.nextInt(_hLim);
    int r1 = _random.nextInt(_hLim);
    int r2 = _random.nextInt(_hLim);
    int r3 = _random.nextInt(_hLim);

    num rslt = _min + (r0 + r1 + r2 + r3) / 4000.0;  //Add the OS back in...
    _sum += rslt; //#DEBUG ONLY
    return( rslt );
  }

  RandomNormal(this._nEle, this._min, this._max, [this._seed = null]) {
    if (_seed == null ) {
      Random r = new Random();
      _seed    = r.nextInt(1000);
    }
    _hLim   = (_max - _min).ceil() * 1000;
    _random = new Random(_seed);
    _rNAr   = [];
    _sum    = 0;//#DEBUG ONLY

    h2("RandomNormal with k: ${_nEle}, Seed: ${_seed}, Min: ${_min}, Max: ${_max}");//#DEBUG ONLY
    for(int n = 0; n < _nEle; n++ ){
      num randomN = _randomN();
      //p("randomN  = ${randomN}");
      LIST_add( _rNAr, randomN );
    }

    h3("Mean = ${_sum/_nEle}");//#DEBUG ONLY
  }
}


new RandomNormal(1000, 80, 120);
new RandomNormal(1000, 80, 120);
new RandomNormal(1000, 80, 120);
new RandomNormal(1000, 80, 120);
new RandomNormal(1000, 80, 120);
new RandomNormal(1000, 80, 120);
new RandomNormal(1000, 80, 120);

Then you can just use it like this to check the mean of sets of 1000 nums generated between a low and high limit. The values are stored in the class so they can be accessed after instantiation.

_swarmii

Answer 5

For me the easiest way is to do:

import 'dart:math';
Random rnd = new Random();
r = min + rnd.nextInt(max - min);
//where min and max should be specified.

Thanks to @adam-singer explanation in here.

Answer 6

Use Random class from dart:math:

import 'dart:math';

main() {
  var rng = new Random();
  for (var i = 0; i < 10; i++) {
    print(rng.nextInt(100));
  }
}

This code was tested with the Dart VM and dart2js, as of the time of this writing.