c# - 正则表达式格式无法按预期工作

Question

我有以下扩展方法:

/*
* text.Format("hello", "no") --> Replaces all appearances of "{hello}" with "no"
*
* For example, if text would have been "{hello} how are you?", the method would have returned "no how are you?"
*/
public static StringBuilder CustomFormat(this StringBuilder text, string name, string value)
{
     return text.Replace(String.Format("{{{0}}}", name), value);
}

/*
*  text.FormatUsingRegex("(?'hello'[A-Z][a-z]{3})", "Mamma mia") --> Replaces the text with the found matching group in the input
*
* For example if text would have been "{hello}oth", the method would have returned "Mammoth"
*/
public static StringBuilder FormatUsingRegex(this StringBuilder text, string regexString, string input)
{
     Regex regex = new Regex(regexString);
     List<string> groupNames = regex.GetGroupNames().ToList();
     Match match = regex.Match(input);
     groupNames.ForEach(groupName => text.CustomFormat(groupName, match.Groups[groupName].Value));
     return text;
}

我正在调用带有以下参数的方法:

 StringBuilder text = new StringBuilder("/index.aspx?xmlFilePath={xmlFilePath}");
 text.FormatUsingRegex("(f=(?'xmlFilePath'.*))?","http://localhost:24674/preview/f=MCicero_temppreview.xml");

我希望 text 像这样结束 /index.aspx?xmlFilePath=MCicero_temppreview.xml，但我却得到了 /index.aspx?xmlFilePath =，就好像该组与输入不匹配。

我试过这个正则表达式并输入 Regex101 , 它似乎工作正常。

这里可能发生了什么？

Answer 1

我认为这是因为您在正则表达式的末尾使用了 ?，并且第一个匹配项是空字符串，因为 ? 表示(在 regex101 解释之后):

Between zero and one time, as many times as possible, giving back as needed

即使在您的 regex101 示例中，您也需要使用/g 模式来捕获组，并且使用/g 在每个字符对之间都有可见的虚线，这意味着正则表达式在那里匹配 - 因为它总是匹配。所以你的函数只返回它捕获的空字符串。

所以试试:

(f=(?'xmlFilePath'.*))