String——Dart

String——Dart

Dart中的String是一系列的UTF-16的字符单元。

1、使用单引号或者双引号均可创建一个String：

  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.";

2、${expression}

使用 ${expression} 可以在字符串中直接添加表达式的值。

如果表达式是一个标识符，{}还可以省略，直接使用$expression即可。

你可以通过Object#toString()方法，得到对象的string表示。

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!');

Note： == 操作符可以检测两个对象是否相等。对String来说，如果它们拥有相同的字符单元序列，那它们就是相等的。

3、字符串连接

单行字符串

Dart中，单行字符串既可以使用 + 号链接，也可以使用相邻的字符串字面值。如下所示：

var s1 = 'String '
    'concatenation'
    " works even over line breaks.";
assert(s1 ==
    'String concatenation works even over '
    'line breaks.');

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

多行字符串

使用三个单引号或者双引号创建多行字符串。

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

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

4、原始字符串—— "raw" string

你可以通过前缀 r 生成一个原始字符串。

var s = r'In a raw string, not even \n gets special treatment.';

如何在String中表示Unicode字符，参见Runes。

编译时常量

字符串字面值是编译时常量，前提是任何字符串插入值的类型也是编译时常量，并且是null、数值类型、字符串、布尔类型 之一。

main() {
  // These work in a const string.
  const aConstNull = null;
  const aConstNum = 0;
  const aConstNum1 = 0.1;
  const aConstBool = true;
  const aConstString = 'a constant string';

  const validConstString = '$aConstNull $aConstNum $aConstNum1 $aConstBool $aConstString';

  print('validConstString:$validConstString');


  // These do NOT work in a const string.
  var aNull = null;
  var aNum = 0;
  var aNum1 = 0.1;
  var aBool = true;
  var aString = 'a string';
  const aConstList = [1, 2, 3];

  //下面这行代码编译不通过
//   const invalidConstString = '$aNum $aBool $aString $aConstList';
}

更多信息请参阅：Strings and regular expressions

参考：https://www.dartlang.org/guides/language/language-tour#strings