前情提要

上篇介紹完資料型別-Numbers後，這篇來到Strings的篇幅，筆者這邊也是採用官方文件及相關連結做一個簡述及驗證，跟著筆者一起學習吧。

內容

筆者這邊還是簡單列一下筆者這邊的開發環境

作業系統:Mac OS
Dart版本:2.17.6
編輯器:Visual Studio Code

Strings

宣告方式

在Dart語言中，Strings代表UTF-16編碼的序列組成，可以使用單引號或雙引號來表示字串

var s1 = 'Single quotes work well for string literals.';
var s2 = "Double quotes work just as well.";
var s3 = 'It\'s easy to escape the string delimiter.';
var s4 = "It's even easier to use the other delimiter.";

動態組合字串

透過${*expression*}可以動態組合字串

var s = 'string interpolation';

assert('Dart has $s, which is very handy.' ==
    'Dart has string interpolation, '
        'which is very handy.');
assert('That deserves all caps. '
        '${s.toUpperCase()} is very handy!' ==
    'That deserves all caps. '
        'STRING INTERPOLATION is very handy!');

==比對字串，要注意的是Dart編譯器比對的是已經轉換成UTF-16編碼過後的一組序列的比對

+運算子

可以透過+運算子組合字串

1 2	var s2 = 'The + operator ' + 'works, as well.'; assert(s2 == 'The + operator works, as well.');

換行宣告字串

若宣告字串中，需要換行宣告，又要保持同一行的字串時，可透過'''三個單引號來表示

var s1 = '''
You can create
multi-line strings like this one.
''';

var s2 = """This is also a
multi-line string.""";

Strings常用操作方法

搜尋字串
1. contains
2. startsWith
3. endsWith
4. indexOf

// Check whether a string contains another string.
assert('Never odd or even'.contains('odd'));

// Does a string start with another string?
assert('Never odd or even'.startsWith('Never'));

// Does a string end with another string?
assert('Never odd or even'.endsWith('even'));

// Find the location of a string inside a string.
assert('Never odd or even'.indexOf('odd') == 6);

擷取字串SubString
1. substrings
2. split
3. codeUnits

// Grab a substring.
assert('Never odd or even'.substring(6, 9) == 'odd');

// Split a string using a string pattern.
var parts = 'progressive web apps'.split(' ');
assert(parts.length == 3);
assert(parts[0] == 'progressive');

// Get a UTF-16 code unit (as a string) by index.
assert('Never odd or even'[0] == 'N');

// Use split() with an empty string parameter to get
// a list of all characters (as Strings); good for
// iterating.
for (final char in 'hello'.split('')) {
  print(char);
}

// Get all the UTF-16 code units in the string.
var codeUnitList = 'Never odd or even'.codeUnits.toList();
assert(codeUnitList[0] == 78);

轉大、小寫UpperCase/LowerCase
1. toUpperCase
2. toLowerCase

// Convert to uppercase.
assert('web apps'.toUpperCase() == 'WEB APPS');

// Convert to lowercase.
assert('WEB APPS'.toLowerCase() == 'web apps');

TrimAndEmpty
1. trim
2. isEmpty
3. isNotEmpty

// Trim a string.
assert('  hello  '.trim() == 'hello');

// Check whether a string is empty.
assert(''.isEmpty);

// Strings with only white space are not empty.
assert('  '.isNotEmpty);

取代Replace

var greetingTemplate = 'Hello, NAME!';
var greeting = greetingTemplate.replaceAll(RegExp('NAME'), 'Bob');

// greetingTemplate didn't change.
assert(greeting != greetingTemplate);

Strings相關詳細API部份，請參考

https://api.dart.dev/stable/2.17.6/dart-core/String-class.html

結論

筆者這邊有跳過一個主題:Runes and grapheme clusters，這個需要花滿多時間去研讀並消化它，畢竟很底層的操作才會需要使用到它，改天再找時間完成另一篇專門文章介紹該主題，剛好筆者參加的另一個長青讀書會(因為已經維持五六年有了)的成員上週在報Encoding相關的主題，筆者屆時會參考該成員提供的教學影片，就先放在參考中提醒筆者，下篇見。

參考

Buy me a coffee

Eugene's Blog

[Flutter讀書會]Dart101:Built-inTypes資料型別-Strings