Html Agility Pack 表中的空值

Question

我正在尝试学习一些基本的抓取，并且感谢这个网站，我已经能够学习很多新东西，但现在我遇到了这个问题......这是我正在使用的代码：

var web = new HtmlWeb();
var doc = web.Load("url");
var nodes = doc.DocumentNode.SelectNodes("//*[@id='hotellist_inner']/div");
StreamWriter output = new StreamWriter("out.txt");

if (nodes != null)
{
    foreach (HtmlNode item in nodes)
    {
        if (item != null && item.Attributes["data-recommended"] != null)
        {
            string line = "";
            var nome = item.SelectSingleNode(".//h3/a").InnerText;
            var rating = item.SelectSingleNode(".//span[@class='rating']").InnerText;
            var price = item.SelectSingleNode("./div[2]/div[3]/div[2]/table/tbody/tr/td[4]/div/strong[1]");
            var discount = item.SelectSingleNode("./div[2]/div[3]/div[2]/table/tbody/tr/td[4]/div/div[1]");
            line = line + nome + "," + rating + "," + price + "," + discount;
            Console.WriteLine(line);
            output.WriteLine(line);
        }
    }
}

前两项（名称和评级）一切正常，但谈到价格和折扣时，我得到的结果是空的。我已经用 chrome scraper 分析了页面（这里是 link），它使用我使用的 xpath 很容易得到结果。我不明白我做错了什么。 任何帮助，将不胜感激！ :D

Answer 1

快速浏览一下您要抓取的网页后，并非所有item 都有价格和折扣信息。您需要正确处理这种情况以避免异常，例如在获取InnerText 之前检查null。您的代码稍作更改就能够在可用的情况下获取价格和折扣信息：

if (item != null && item.Attributes["data-recommended"] != null)
{
    string line = "";
    var nome = item.SelectSingleNode(".//h3/a").InnerText;
    var rating = item.SelectSingleNode(".//span[@class='rating']").InnerText;
    var price = item.SelectSingleNode("./div[2]/div[3]/div[2]/table/tbody/tr/td[4]/div/strong[1]");
    var discount = item.SelectSingleNode("./div[2]/div[3]/div[2]/table/tbody/tr/td[4]/div/div[1]");
    //set priceString to empty string if price is null, else set it to price.InnerText
    var priceString = price == null ? "" : price.InnerText;
    //do similar step for discountString
    var discountString = discount == null ? "" : discount.InnerText;
    line = line + nome + "," + rating + "," + priceString + "," + discountString;
    Console.WriteLine(line);
    output.WriteLine(line);
}