How can I strip HTML tags from a string in ASP.NET

Question

Using ASP.NET, how can I strip the HTML tags from a given string reliably (i.e. not using regex)? I am looking for something like PHP's strip_tags.

Example:

<ul><li>Hello</li></ul>

Output:

"Hello"

I am trying not to reinvent the wheel, but I have not found anything that meets my needs so far.

Answer 1

If it is just stripping all HTML tags from a string, this works reliably with regex as well. Replace:

<[^>]*(>|$)

with the empty string, globally. Don't forget to normalize the string afterwards, replacing:

[\s\r\n]+

with a single space, and trimming the result. Optionally replace any HTML character entities back to the actual characters.

Note:

1. There is a limitation: HTML and XML allow > in attribute values. This solution will return broken markup when encountering such values.
2. The solution is technically safe, as in: The result will never contain anything that could be used to do cross site scripting or to break a page layout. It is just not very clean.
3. As with all things HTML and regex:
   Use a proper parser if you must get it right under all circumstances.

Answer 2

string result = Regex.Replace(anytext, @"<(.|\n)*?>", string.Empty);

Answer 3

For the second parameter,i.e. keep some tags, you may need some code like this by using HTMLagilityPack:

public string StripTags(HtmlNode documentNode, IList keepTags)
{
    var result = new StringBuilder();
        foreach (var childNode in documentNode.ChildNodes)
        {
            if (childNode.Name.ToLower() == "#text")
            {
                result.Append(childNode.InnerText);
            }
            else
            {
                if (!keepTags.Contains(childNode.Name.ToLower()))
                {
                    result.Append(StripTags(childNode, keepTags));
                }
                else
                {
                    result.Append(childNode.OuterHtml.Replace(childNode.InnerHtml, StripTags(childNode, keepTags)));
                }
            }
        }
        return result.ToString();
    }

More explanation on this page: http://nalgorithm.com/2015/11/20/strip-html-tags-of-an-html-in-c-strip_html-php-equivalent/

Answer 4

Regex.Replace(htmlText, "<.*?>", string.Empty);

Answer 5

using System.Text.RegularExpressions;

string str = Regex.Replace(HttpUtility.HtmlDecode(HTMLString), "<.*?>", string.Empty);

Answer 6

For those of you who can't use the HtmlAgilityPack, .NETs XML reader is an option. This can fail on well formatted HTML though so always add a catch with regx as a backup. Note this is NOT fast, but it does provide a nice opportunity for old school step through debugging.

public static string RemoveHTMLTags(string content)
    {
        var cleaned = string.Empty;
        try
        {
            StringBuilder textOnly = new StringBuilder();
            using (var reader = XmlNodeReader.Create(new System.IO.StringReader("<xml>" + content + "</xml>")))
            {
                while (reader.Read())
                {
                    if (reader.NodeType == XmlNodeType.Text)
                        textOnly.Append(reader.ReadContentAsString());
                }
            }
            cleaned = textOnly.ToString();
        }
        catch
        {
            //A tag is probably not closed. fallback to regex string clean.
            string textOnly = string.Empty;
            Regex tagRemove = new Regex(@"<[^>]*(>|$)");
            Regex compressSpaces = new Regex(@"[\s\r\n]+");
            textOnly = tagRemove.Replace(content, string.Empty);
            textOnly = compressSpaces.Replace(textOnly, " ");
            cleaned = textOnly;
        }

        return cleaned;
    }