How to capitalize the first letter of a string in dart?

Question

How do I capitalize the first character of a string, while not changing the case of any of the other letters?

For example, "this is a string" should give "This is a string".

Solution 1

Since dart version 2.6, dart supports extensions:

extension StringExtension on String {
    String capitalize() {
      return "${this[0].toUpperCase()}${this.substring(1).toLowerCase()}";
    }
}

So you can just call your extension like this:

import "string_extension.dart";

var someCapitalizedString = "someString".capitalize();

Solution 2

Copy this somewhere:

extension StringCasingExtension on String {
  String toCapitalized() => length > 0 ?'${this[0].toUpperCase()}${substring(1).toLowerCase()}':'';
  String toTitleCase() => replaceAll(RegExp(' +'), ' ').split(' ').map((str) => str.toCapitalized()).join(' ');
}

Usage:

// import StringCasingExtension

final helloWorld = 'hello world'.toCapitalized(); // 'Hello world'
final helloWorld = 'hello world'.toUpperCase(); // 'HELLO WORLD'
final helloWorldCap = 'hello world'.toTitleCase(); // 'Hello World'

Solution 3

Substring parsing in the other answers do not account for locale variances. The toBeginningOfSentenceCase() function in the intl/intl.dart package handles basic sentence-casing and the dotted "i" in Turkish and Azeri.

import 'package:intl/intl.dart' show toBeginningOfSentenceCase;

print(toBeginningOfSentenceCase('this is a string'));

Solution 4

void main() {
  print(capitalize("this is a string"));
  // displays "This is a string"
}

String capitalize(String s) => s[0].toUpperCase() + s.substring(1);

See this snippet running on DartPad : https://dartpad.dartlang.org/c8ffb8995abe259e9643

Solution 5

There is a utils package that covers this function. It has some more nice methods for operation on strings.

Install it with :

dependencies:
  basic_utils: ^1.2.0

Usage :

String capitalized = StringUtils.capitalize("helloworld");

Github:

https://github.com/Ephenodrom/Dart-Basic-Utils

View more solutions

Comments

[Rishi Dua]

will complain when string is empty or not long enough.

[Giraldi]

I don't think this checks for null.

[Jawand Singh]

@RishiDua well as a dev, (by default) we have the responsibility to check for those conditions 🐱‍👤

[Dani]

nice package. Thanks for sharing

[Nguyễn Văn Phong]

While this may answer the question, you should add more note to explain in order to help the OP know the reason why.

[TomTom101]

s[0].toUpperCase() + s.substring(1).toLowerCase(); in case the string is all upper case to start with.

[Luciano Rodríguez]

Extension should return return "${this[0].toUpperCase()}${this.substring(1).toLowerCase()}"‌​;. If not it will capitalize correctly 'this' but not 'THIS'.

[Hannah Stark]

don't you normally check if a value is valid before operating with it?

[FluffyKitten]

Code-only answers are discouraged on Stack Overflow because they don't explain how it solves the problem. Please edit your answer to explain what the code does and how it answers the question, so that it is useful for other users also as well as the OP.

[Palejandro]

good solution, but doesn't work with letters with diacritics

[Ndimah]

it's normal because of the regex if you wish to do it adjust the regex to include those letters

[Vikas Jangra]

We either have to check isEmpty inside capitalize() or leave it up to the caller. My preference is for the caller so the code doesn't need to get littered with .isEmpty() checks. You can add if (isEmpty) return this as the first line.

[Lucas Chwe]

gotta check if this is empty to avoid the crash. i dont think toLowerCase() would crash with an empty string and neither should your extension

[Ashan]

str.capitalize is not defined. So you use str.inCaps

[Maciej]

you should add some checks if string is not null - eg: if (this == null || this == "") return "";

[Gustavo Rodrigues]

This with addition to the extension method answer should be the answer. If you already use the intl package there is no reason to reinvent the wheel with the extension.

[jwehrle]

Just what I was looking for. Thanks!

[Dario Brux]

Great library!!

[WillHaslett]

Looks great. Use with caution as there's only one test, however much you may dig the test case. String mockText = 'This is-Some_sampleText. YouDig?';

[BIS Tech]

Uncaught Error: RangeError (index): Index out of range: no indices are valid: 0

[BIS Tech]

final helloWorld = 'hello world'.capitalizeFirstofEach;

[BIS Tech]

Uncaught Error: RangeError (index): Index out of range: no indices are valid: 0

[BIS Tech]

String data = allWordsCapitilize('THIS IS A TEST') ;

[Tom]

I can't find any reference to this. Can you provide source?

[Jing Wey]

Sorry, its under a plugin, my bad. Use this : link . It has a lot of useful utilities

[Iván Yoed]

Hey! Thanks for the response. I'm curious, what would be the benefit of characters?

[Gerry]

I thought I liked Dart.... but this is quite special. Why wouldn't they have something like this in the core language? I wonder what else is missing!

[user3056783]

Yes this is correct answer if you want to handle different locales in the right way. +1

[Ndimah]

I think a simpler Implementation is to handle the whitespace, not the words in the regex just change it with str = str.trim().splitMapJoin( RegExp(r'\s+'), onMatch: (m) => ' ', onNonMatch: (n) { return '${n.substring(0,1).toUpperCase()}${n.substring(1).toLowerCa‌​se()}'; }, ).trim();

[tim-montague]

@GustavoRodrigues - Even if you are not currently using Intl this is a better answer, because this package is maintained by the Flutter / Dart team, while the extension method has to be maintained by the developer.

[positrix]

I just use: someString = someString[0].toUpperCase() + someString.substring(1).toLowerCase();

[benten]

the best solution

[Peter Bruins]

That will capitalize the whole string, instead of the first character.