无法识别Dart RegExp空白 [英] Dart RegExp white spaces is not recognized

问题描述

我正在尝试为用户名实现一个正则表达式模式，以允许英文字母，阿拉伯字母，数字，破折号和空格。

如果输入字符串，以下模式始终返回不匹配的内容即使在模式中包含\s也有一个空格

 模式_usernamePattern = r'^ [a-zA-Z0-9\u0621 -\u064A\-\s] {3,30} $'; 
  

我还尝试用; "

编辑：事实证明flutter为 Right-左标记或左至右标记；当使用具有LTR或RTL混合语言的文本字段时。此附加标记是一个Unicode字符，已添加到文本中。由于此附加字符，上述正则表达式失败。要解决此问题，只需对这些字符执行replaceAll即可。在此处阅读更多信息： https://github.com/flutter/flutter/issues/56514。

解决方案

这是一个非常讨厌的问题，值得在此处进行解答。

如源：

  ///当在RTL字段中输入LTR文本或在
中输入RTL文本// / LTR字段，[LRM]（https://en.wikipedia.org/wiki/从左至右标记）或
 /// [RLM]（https://en.wikipedia.org/wiki/ Right-to-left_mark）字符将分别插入
 ///与空白字符一起。这是为了
 ///消除空格中的歧义方向，并确保适当的插入符号
 ///位置。这些字符会影响字符串的长度，在与其他
 ///进行字符串比较之类的操作时，可能需要解析
 ///。 
  

这是很好的意图，当您使用混合LTR / RTL文本模式时可能会引起问题（因为它是情况），并且必须确保确切的字段长度，等等。

建议解决方案是删除所有左右标记：

  void main（）{
 final String lrm ='aaaa \u {200e} bbbb'; 
 print（‘lrm： $ lrm，长度为$ {lrm.length}’）； 
 
最终字符串lrmFree = lrm.replaceAll（RegExp（r'\u {200e}'，unicode：true），’’）; 
 print（’lrmFree： $ lrmFree，长度为$ {lrmFree.length}’）； 
} 
  

相关：从右向左（RTL）颤动

I'm trying to implement a regex pattern for username that allows English letters, Arabic letters, digits, dash and space.

The following pattern always returns no match if the input string has a space even though \s is included in the pattern

Pattern _usernamePattern = r'^[a-zA-Z0-9\u0621-\u064A\-\s]{3,30}$';

I also tried replacing \s with " " and \\s but the regex always returns no matches for any input that has a space in it.

Edit: It turns out that flutter adds a unicode character for "Right-To-Left Mark" or "Left-To-Right Mark" when using a textfield with a mix of languages that go LTR or RTL. This additional mark is a unicode character that's gets added to the text. The regex above was failing because of this additional character. To resolve the issue simply do a replaceAll for these characters. Read more here: https://github.com/flutter/flutter/issues/56514.

解决方案

This is a fairly nasty problem and worth documenting in an answer here.

As documented in the source:

  /// When LTR text is entered into an RTL field, or RTL text is entered into an
  /// LTR field, [LRM](https://en.wikipedia.org/wiki/Left-to-right_mark) or
  /// [RLM](https://en.wikipedia.org/wiki/Right-to-left_mark) characters will be
  /// inserted alongside whitespace characters, respectively. This is to
  /// eliminate ambiguous directionality in whitespace and ensure proper caret
  /// placement. These characters will affect the length of the string and may
  /// need to be parsed out when doing things like string comparison with other
  /// text.

While this is well-intended it can cause problems when you work with mixed LTR/RTL text patterns (as it is the case here) and have to ensure exact field length, etc.

The suggested solution is to remove all left-right-marks:

void main() {
  final String lrm = 'aaaa \u{200e}bbbb';
  print('lrm: "$lrm" with length ${lrm.length}');
  
  final String lrmFree = lrm.replaceAll(RegExp(r'\u{200e}', unicode: true), '');
  print('lrmFree: "$lrmFree" with length ${lrmFree.length}');
}

Related: right-to-left (RTL) in flutter

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