C# HtmlAgilityPack : Error looping throough nodes

Question

I'm looping through some <li> tags and within this tag there is an <a> tag of class="track-visit-website":

<li><a class="track-visit-website" href="abc1">Anchor1</a></li>

I want to grab the href of <a> tags. But in some <li> there is no <a> tags so my code is throwing error.

My Code is :

List<string> Website = new List<string>();
HtmlDocument hoteleWebsiteDoc = new HtmlDocument();
hoteleWebsiteDoc.LoadHtml(hotels.InnerHtml);

var hotelWebsite = from lnks in hoteleWebsiteDoc.DocumentNode.Descendants()
                    where lnks.Name == "a" && lnks.Attributes.Contains("class") &&
                      lnks.Attributes["class"] != null &&
                      lnks.Attributes["class"].Value.Contains("track-visit-website") &&
                      lnks.InnerText.Trim().Length > 0
                    select new
                    {
                     Url = lnks.Attributes["href"].Value,
                    };

foreach (var website in hotelWebsite)
{
    if (!string.IsNullOrEmpty(website.Url) || !string.IsNullOrWhiteSpace(website.Url))
        Website.Add(website.Url.Trim());
    else
        Website.Add(" ");
}

What should I do ? I thought of checking first whether the tag exists or not and then execute the code. But how can i check whether the tag exists or not? Or is there some other way ?

Answer 1

var items = hoteleWebsiteDoc
           .DocumentNode.SelectNodes("//li/a[@class='track-visit-website']");

if(items!=null)
{
    var links = items.Select(a => a.Attributes["href"].Value).ToList();
}

Answer 2

This solution take into account the possible case in which the a tag not contains the href attribute, for example :

<li>
   <a class='track-visit-website' href='abc1'>Anchor1</a>
</li>
<li>
   <a class='track-visit-website'>Anchor 2</a>
</li> 
<li> 
</li>

---

var hoteleWebsiteDoc = (from element in doc.DocumentNode.Descendants("a")
                        where element.ParentNode.Name.Equals("li") && 
                        element.Attributes.Contains("class") &&
                        element.Attributes.Contains("href") &&
                        element.Attributes["class"].Value.Equals("track-visit-website")
                        select new
                                 {
                                   URL = element.Attributes["href"].Value
                                 }).ToList();

foreach (var obj in hrefsList)
{
   Console.WriteLine(obj.URL);
}

Or if you want to keep the other solution instead you can change your code for this to check if contains the href attribute :

if (items != null)
{
   var links = items.Where(a => a.Attributes.Contains("href")).Select(a => a.Attributes["href"].Value).ToList();
}