我没有看到 Dart 字符串被视为字符列表。我假设我必须使用 for 循环,这会很蹩脚。
另一种实现(使用基本多语言平面之外的字符):
"A string".runes.forEach((int rune) {
var character=new String.fromCharCode(rune);
print(character);
});
不幸的是字符串目前不可迭代,所以你必须使用像这样的for循环
for(int i=0; i<s.length; i++) {
var char = s[i];
}
请注意,Dart 没有字符类,因此 string[index] 将返回另一个字符串。
使用 Flutter 角色类
import 'package:flutter/material.dart';
var characters = aString.characters;
正确迭代
String
的扩展:
extension on String {
/// To iterate a [String]: `"Hello".iterable()`
Iterable<String> iterable() sync* {
for (var i = 0; i < length; i++) {
yield this[i];
}}}
像这样使用它:
expect("Hello".iterable(), ["H", "e", "l", "l", "o"]);
但是,如果添加 Characters 包:
import "package:characters/characters.dart";
然后您可以使用扩展来使用简单字符或 Unicode 字素正确迭代
String
:
extension on String {
/// To iterate a [String]: `"Hello".iterable()`
/// This will use simple characters. If you want to use Unicode Grapheme
/// from the [Characters] library, passa [chars] true.
Iterable<String> iterable({bool unicode = false}) sync* {
if (unicode) {
var iterator = Characters(this).iterator;
while (iterator.moveNext()) {
yield iterator.current;
}
} else
for (var i = 0; i < length; i++) {
yield this[i];
}
}
}
证明它有效:
test('String.iterable()', () {
expect("Hello".iterable(), ["H", "e", "l", "l", "o"]);
expect("Hello".iterable(unicode: true), ["H", "e", "l", "l", "o"]);
expect("😊".iterable().length, 2);
expect("😊".iterable().map((s) => s.codeUnitAt(0)), [55357, 56842]);
expect("😊".iterable(unicode: true).length, 1);
expect("😊".iterable(unicode: true), ["😊"]);
});
extension on String {
//toArray1 method
List toArray1() {
List items = [];
for (var i = 0; i < this.length; i++) {
items.add(this[i]);
}
return items;
}
//toArray2 method
List toArray2() {
List items = [];
this.split("").forEach((item) => items.add(item));
return items;
}
}
main(List<String> args) {
var str = "hello world hello world hello world hello world hello world";
final stopwatch1 = Stopwatch()..start();
print(str.toArray1());
print('str.toArray1() executed in ${stopwatch1.elapsed}');
final stopwatch2 = Stopwatch()..start();
print(str.toArray2());
print('str.toArray2() executed in ${stopwatch2.elapsed}');
}
上面是使用 for 循环和 foreach 的示例,但我测试的结果是,foreach 的运行速度比 for 循环快得多。抱歉,如果我错了,但这是我的测试。
这也可以是解决方案:如果你觉得简单就使用它
String text = "findlastcharacter";
var array = text.split('');
array.forEach((element) {
print(element); // iterating char by char
});
String lastchar = array[array.length - 1];
print('last char is = $lastchar'); // last char is = r
谢谢
import 'package:characters/characters.dart';
String myString = "Hi";
for (var char in myString.characters) {
print(char);
}
H
i
如果您从字符开始,需要注意的一件事是它们将被转换为字符串。
Characters myCharacters = "Hi.characters".characters;
for (var char in myCharacters) {
assert(char is String);
print(char);
}
H
i
只是一个快速概述,您应该确实使用字符包:
import "package:characters/characters.dart";
main() {
print("🧔♂️".characters);
print("🧔♂️".characters.length);
print("🧔♂️".runes);
print("🧔♂️".runes.length);
print("🧔♂️".codeUnits);
print("🧔♂️".codeUnits.length);
}
将会输出
🧔♂️
1
(129492, 8205, 9794, 65039)
4
[55358, 56788, 8205, 9794, 65039]
5