How to capitalize the first letter of a string in

问题:

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".

回答1:

main() {
  String s = 'this is a string';
  print('${s[0].toUpperCase()}${s.substring(1)}');
}

回答2:

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

Alternatively you can use the strings package, see capitalize.

回答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';
...
String sentence = toBeginningOfSentenceCase('this is a string'); // This is a string

回答4:

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

回答5:

You should also check if the string is null or empty.

String capitalize(String input) {
  if (input == null) {
    throw new ArgumentError("string: $input");
  }
  if (input.length == 0) {
    return input;
  }
  return input[0].toUpperCase() + input.substring(1);
}

回答6:

To check for null and empty string cases, also using the short notations:

  String capitalizeFirstLetter(String s) =>
  (s?.isNotEmpty ?? false) ? '${s[0].toUpperCase()}${s.substring(1)}' : s;

回答7:

String capitalize(String s) => (s != null && s.length > 1)
    ? s[0].toUpperCase() + s.substring(1)
    : s != null ? s.toUpperCase() : null;

It passes tests:

test('null input', () {
  expect(capitalize(null), null);
});
test('empty input', () {
  expect(capitalize(''), '');
});
test('single char input', () {
  expect(capitalize('a'), 'A');
});
test('crazy input', () {
  expect(capitalize('?a!'), '?a!');
});
test('normal input', () {
  expect(capitalize('take it easy bro!'), 'Take it easy bro!');
});

回答8:

var orig = "this is a string";
var changed = orig.substring(0, 1).toUpperCase + orig.substring(1)

回答9:

Some of the more popular other answers don't seem to handle null and ''. I prefer to not have to deal with those situations in client code, I just want a String in return no matter what - even if that means an empty one in case of null.

String upperCaseFirst(String s) => (s??'').length<1 ? '' : s[0].toUpperCase() + s.substring(1)

回答10:

void allWordsCapitilize (String str) {
    return str.toLowerCase().split(' ').map((word) {
      String leftText = (word.length > 1) ? word.substring(1, word.length) : '';
      return word[0].toUpperCase() + leftText;
    }).join(' ');
}
allWordsCapitilize('THIS IS A TEST'); //This Is A Test