如何在范围内拆分字符串

Question

我是 Flutter 的新手，我需要你的帮助。 谁能帮助我如何将这段代码行从 JavaScript 写到 Flutter：

onInputChange(event, backspace) {
let newVal = event.replace(/\D/g, '');
if (backspace && newVal.length <= 6) {
  newVal = newVal.substring(0, newVal.length - 1);
}
if (newVal.length === 0) {
  newVal = '';
} else if (newVal.length <= 3) {
  newVal = newVal.replace(/^(\d{0,3})/, '($1)');
} else if (newVal.length <= 6) {
  newVal = newVal.replace(/^(\d{0,3})(\d{0,3})/, '($1) $2'); 
} else if (newVal.length <= 10) {
  newVal = newVal.replace(/^(\d{0,3})(\d{0,3})(\d{0,4})/, '($1) $2-$3');
} else {
  newVal = newVal.substring(0, 10);
  newVal = newVal.replace(/^(\d{0,3})(\d{0,3})(\d{0,4})/, '($1) $2-$3');
}
this.ngControl.valueAccessor.writeValue(newVal);

}

我在 .splitMapJoin 中看到了一些东西，但我做不到。

Answer 1

试试replaceFirstMapped

var value = '1234567890';
var regExp = RegExp(r'^(\d{0,3})(\d{0,3})(\d{0,4})');
var phoneNumber = value.replaceFirstMapped(regExp, (match) {
  return '(${match.group(1)}) ${match.group(2)}-${match.group(3)}';
});

print(phoneNumber); //(123) 456-7890

问题编辑后更新

你需要这样的东西吗：

format(String value) {
  var regExp2 = RegExp(r'^(\d{0,3})(\d{0,3})(\d{0,4})');
  return value.replaceFirstMapped(regExp2, (match) {
    var res = '';
    if (match.group(1).isNotEmpty) {
      res += '(${match.group(1)})';
    }
    if (match.group(2).isNotEmpty) {
      res += ' ${match.group(2)}';
    }

    if (match.group(3).isNotEmpty) {
      res += '-${match.group(3)}';
    }

    return res;
  });
}

var value = '1234567890';
var value2 = '12345';

print(format(value)); //(123) 456-7890
print(format(value2)); //(123) 45