Using Regex.Replace with MatchEvaluator function in C#

Question

I have the following piece of code,

 private void ReplaceVariables(DynamicForm form, DynamicEmailTemplate emailTemplate, List<DynamicFieldValue> fieldValues)
 {
     Regex regex = new Regex("\\?([\\w-]+)\\?", RegexOptions.IgnoreCase);

     // Replace Form Display Title Variables
     MatchCollection formDisplayTitleRegexMatches = regex.Matches(form.FormDisplayTitle);

     if (formDisplayTitleRegexMatches.Count > 0)
     {
         foreach (Match formDisplayTitleRegexMatch in formDisplayTitleRegexMatches)
         {
             foreach (var fieldValue in fieldValues)
             {
                 var formformDisplayTitleRegexMatchRemovedQuestionMarks = formDisplayTitleRegexMatch.Groups[1].Value;

                 if (formformDisplayTitleRegexMatchRemovedQuestionMarks.Equals(fieldValue.FieldCode))
                 {
                     form.FormDisplayTitle = form.FormDisplayTitle.Replace(formDisplayTitleRegexMatch.Value, fieldValue.Value);
                 }
             }
         }
     }
}

IEnumerable<string> labelsInEmailTemplate = emailTemplate
  .Entries
  .Select(x => x.FormField.FieldDefinition.FieldLabel);

foreach (string labelInEmailTemplate in labelsInEmailTemplate)
{
    MatchCollection labelRegexMatches = regex.Matches(labelInEmailTemplate);

    if (labelRegexMatches.Count > 0)
    {
        foreach (Match labelRegexMatch in labelRegexMatches)
        {
            foreach (DynamicFieldValue fieldValue in fieldValues)
            {
                string labelRegexMatchRemovedQuestionMarks = labelRegexMatch.Groups[1].Value;

                if (labelRegexMatchRemovedQuestionMarks.Equals(fieldValue.FieldCode))
                {
                    DynamicEmailTemplateEntry emailTemplateEntryToUpdate = emailTemplate
                        .Entries
                        .Find(x => x
                            .FormField
                            .FieldDefinition
                            .FieldLabel
                            .Contains(labelRegexMatch.Value));

                    emailTemplateEntryToUpdate
                        .FormField
                        .FieldDefinition
                        .FieldLabel = emailTemplateEntryToUpdate
                             .FormField
                             .FieldDefinition
                             .FieldLabel
                             .Replace(labelRegexMatch.Value, WebUtility.HtmlEncode(fieldValue.Value));
                }
            }
        }
    }
}

Sample title variable can be - ?MY_Title? and ?MyName?

I have 2 foreach loops, instead, is it possible to use MatchEvaluator and a delegate passing to Regex.Replace?

Made another update, is it possible to use Replace when I have 2 foreach loops, as I cannot update the record through foreach loop.

Dmitrii Bychenko · Accepted Answer · 2023-01-13 19:05:57Z

2

Yes, you can try rewriting you code into Regex.Replace, something like this:

Regex regex = new Regex(@"\?[\w-]+\?", RegexOptions.IgnoreCase);

form.FormDisplayTitle = regex.Replace(form.FormDisplayTitle, match => {
  // get rid of leading and trailing ?
  var name = match.Value.Trim('?');

  // check if match corresponds to any FieldCode
  foreach (var fieldValue in fieldValues) 
    if (name.Equals(fieldValue.FieldCode))
      return fieldValue.Value; // Code found, Value returned
  
  // Unknown FieldCode, do nothing (return match intact)
  return match.Value; 
});

Here for each match lambda function is called where we should return the substitution: either fieldValue.Value or match itself - match.Value - if value has not been found.

Update: The second fragment can be rewritten as follow:

// For each entry in emailTemplate.Entries
foreach (var DynamicEmailTemplateEntry entry in emailTemplate.Entries) {
  // given lable teemplate...
  string labelTemplate = entry
    .FormField
    .FieldDefinition
    .FieldLabel;

  // ... we compute actual label
  string updatedLabel = regex.Replace(labelTemplate, match => {
    var name => match.Value.Trim('?');
  
    // either FieldValue or match as it is
    return fieldValue
      .Where(fv => fv.FieldCode == name)
      .Select(fv => fv.Value)
      .FirstOrDefault(match.Value);
  });

  // which we assign to template 
  entry
    .FormField
    .FieldDefinition
    .FieldLabel = updatedLabel; 
}

edited Jan 13, 2023 at 19:05

answered Jan 13, 2023 at 1:00

Dmitrii Bychenko

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2 Comments

tRuEsAtM Over a year ago

Solution works great, thanks! I updated my question, with another method there are 2 foreach loops, and I cannot update the record in foreach as it is read-only. Is it possible to use Replace there?

Dmitrii Bychenko Over a year ago

@tRuEsAtM: The very same princile: for each entry within Entries we get template, replace placeholders with a help of regular expresssions; then we assign label back.

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