How to get the CSS class name or style properties from HTML document using C#

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Can any one help me out how to get the CSS Class name or Style properties of a Text / Keyword from html document using C#?
Say I am passing the text "Sample Text" from code.
I have a html document which has following code

<div class="sampleclass">
Sample Text
</div>

I need to get the result as sampleclass when Sample Text is passed.

What I have tried:

I have used HTMLAgility library , I can get the text based on class name but I need the other way around to get class name when text is passed.

Posted 9-Jan-17 7:27am

Dudyalu Sravan Kumar Reddy

Updated 9-Jan-17 7:56am

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Thomas Daniels · Accepted Answer · 2017-01-09T07:46:00

If you have a HtmlDocument (using HtmlAgilityPack), you can use .DocumentNode.Descendants() to get all descendants, and using the LINQ extension methods, you can search for the element containing 'Sample Text' and get its class:

C#

string html = @"<!DOCTYPE html>
<html>
<head><title>Sample document</title></head>
<body>
<div class=""sampleclass"">
Sample Text
</div>
</body>
</html>";

HtmlDocument doc = new HtmlDocument();
doc.LoadHtml(html);

HtmlNode foundNode = doc.DocumentNode.Descendants().Where(x => x.InnerHtml.Trim() == "Sample Text").FirstOrDefault();
string classAttribute = foundNode?.Attributes["class"]?.Value;

.Where[^] filters the descendants using the predicate x => x.InnerHtml.Trim() == "Sample Text", which means that for an element 'x' in the list of descendants, the trimmed InnerHTML of 'x' must be "Sample Text". .FirstOrDefault[^] returns the first found element, or null if no element is found.

When the node is found, the attribute is fetched from the node. Note that I used ?. instead of just . because ?. is a null-conditional operator[^]. foundNode?.Attributes["class"] means "if foundNode is null, then this expression evaluates to null; if foundNode is not null, then this expression executes .Attributes["class"]". ?.Value works in the same way. Using this operator avoids a few null checks. If foundNode is null or if it doesn't have a class attribute, then classAttribute is null too.