如何从省道的范围中得到一个随机数？

Range can be found with a simple formula as follows

Random rnd;
int min = 5;
int max = 10;
rnd = new Random();
r = min + rnd.nextInt(max - min);
print("$r is in the range of $min and $max");

import 'dart:math';


final _random = new Random();


/**
* Generates a positive random integer uniformly distributed on the range
* from [min], inclusive, to [max], exclusive.
*/
int next(int min, int max) => min + _random.nextInt(max - min);

A simpler way of doing this is to use the nextInt method within Random:

// Random 50 to 100:
int min = 50;
int max = 100;
int selection = min + (Random(1).nextInt(max-min));

https://api.dartlang.org/stable/2.0.0/dart-math/Random-class.html

You can achieve it via Random class object random.nextInt(max) . The nextInt() method requires a max limit. The random number starts from 0 and the max limit itself is exclusive.

import 'dart:math';
Random random = new Random();
int randomNumber = random.nextInt(100); // from 0 upto 99 included

If you want to add the min limit, add the min limit to the result

int randomNumber = random.nextInt(90) + 10; // from 10 upto 99 included

import 'dart:math';


Random rnd = new Random();
// Define min and max value
int min = 1, max = 10;
//Getting range
int num = min + rnd.nextInt(max - min);
print("$num is in the range of $min and $max");

To generate a random double within a range, multiply a random int with a random double.

import 'dart:math';
Random random = new Random();
int min = 1, max = 10;
double num = (min + random.nextInt(max - min)) * random.nextDouble();

Generates a random integer uniformly distributed in the range from [min] to [max], both inclusive.

int nextInt(int min, int max) => min + _random.nextInt((max + 1) - min);

This is really late, but this for anyone who still has the question.

The easiest way to get a random number between a min and a max is the following :

import 'dart:math';


int max = 10;


int randomNumber = Random().nextInt(max) + 1;

The math module in dart has a function called nextInt. This will return an integer from 0 (including 0 ) to max - 1 ( exluding max ). I want a number 1 to 10, hence I add 1 to the nextInt result.

It can be achieved exactly as you intended by creating extension on int to get random int value. For example:

import 'dart:math';


import 'package:flutter/foundation.dart';


extension RandomInt on int {
static int generate({int min = 0, @required int max}) {
final _random = Random();
return min + _random.nextInt(max - min);
}
}

And you can use this in your code like so:

List<int> rands = [];
for (int j = 0; j < 19; j++) {
rands.add(RandomInt.generate(max: 50));
}

Note that static extension methods can't be called on type itself (e.g. int.generate(min:10, max:20)), but instead you have to use extension name itself, in this example RandomInt. For detailed discussion, read here.

When I was making a Tetris game, I had to rotate the x-axis. For this, I wrote the following codes. I hope it will be useful for you too:

Random rnd = Random();
int min = 0;
int max = 23;
class Block {
int x = min + rnd.nextInt(max - min);
}

To Generate a random positive integer between a given range:

final _random = new Random();


// from MIN(inclusive), to MAX(exclusive).
int randomBetween(int min, int max) => min + _random.nextInt(max - min);


// from MIN(inclusive), to MAX(inclusive).
int randomBetween(int min, int max) => min + _random.nextInt((max+1) - min);


// from MIN(exclusive), to MAX(exclusive).
int randomBetween(int min, int max) => (min+1) + _random.nextInt(max - (min+1));