Generating a list through a loop on dart

Question

I wanted to make a list of colors in dart for my app but, since I don't want this list to be enormous, I'd like to know if there's a way to generate a list given a particular condition. The list is this one:

List dateColors = [
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white,
    Colors.white
  ];

Thierry · Accepted Answer · 2021-03-11 21:47:11Z

2

If you want to fill a List with the same value, use filled:

import 'package:flutter/material.dart';

void main() {
  final dateColors = List.filled(31, Colors.white);
  print(dateColors);
  // [Color(0xffffffff), ..., Color(0xffffffff)], a total of 31 Colors.white.
}

answered Mar 11, 2021 at 21:47

Thierry

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drogel · Accepted Answer · 2021-03-11 21:01:56Z

2

It's funny that you mentioned the key word here: generate. That's the constructor of the List type you are looking for.

List<int>.generate(3, (int index) => index * index); // [0, 1, 4]

Check the docs for more info on this constructor.

In your case, you could discard the index that the generate constructor is giving you, to build a list that is made of the same objects repeating over and over again. Consider this snippet as an example that may suit your needs

import 'package:flutter/material.dart';

void main() {
  final colors = List<Color>.generate(20, (_) => Colors.white); 
  print(colors);
  // Prints [Color(0xffffffff), ..., Color(0xffffffff)], a total of twenty Colors.white.
}

you can see that it prints a list of 20 Colors, and all of them are white.

edited Mar 11, 2021 at 21:01

answered Mar 11, 2021 at 19:26

drogel

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2 Comments

AndryCraft69 Over a year ago

So how would that be in my case? List<Color>.generate(31, (Color i) => i=Colors.white);?

drogel Over a year ago

You are on the right path, but the line you suggested won't work because generate will provide you with an index of type int, and not with a color. I should have built an example that was more related to your question. Consider the example I've added to my edited answer, hope it suits your needs.

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