尝试使用HtmlAgilityPack从网页中提取数据

好吧，我检查了。我们使用的XPath根本不正确。当您尝试找到错误所在时，真正的乐趣就开始了。

只要检查出您正在使用的页面的源代码，就可以避免许多错误，这些错误会阻碍XPath甚至包含多个HTML标记...

Chrome Dev Tools和您使用的工具可在浏览器校正的dom树上使用（全部打包到单个html节点中，添加了一些tbody等）。

由于html结构只是被破坏了，因此成为了HtmlAgilityPack的解析器。

就目前情况而言，您可以使用RegExp或仅搜索源中的已知元素（速度更快，但敏捷性更低）。

例如：

...
using System.Net; //required for Webclient
...
        class Program
        {
            //entry point of console app
            static void Main(string[] args)
            {
                // url to download
                // "var" means I am too lazy to write "string" and let compiler decide typing
                var url = @"http://www.dsebd.org/displayCompany.php?name=NBL";

                // creating object in using makes Garbage Collector delete it when using block ends, as opposed to standard cleaning after whole function ends
                using (WebClient client = new WebClient()) // WebClient class inherits IDisposable
                {

                    // simply download result to string, in this case it will be html code
                    string htmlCode = client.DownloadString(url);
                    // cut html in half op position of "Last Trade:"
                    // searching from beginning of string is easier/faster than searching in middle
                    htmlCode = htmlCode.Substring(
                        htmlCode.IndexOf("Last Trade:")
                        );
                    // select from .. to .. and then remove leading and trailing whitespace characters
                    htmlCode = htmlCode.Substring("2\">", "</font></td>").Trim();
                    Console.WriteLine(htmlCode);
                }
                Console.ReadLine();
            }
        }
        // http://stackoverflow.com/a/17253735/3147740 <- copied from here
        // this is Extension Class which adds overloaded Substring() I used in this code, it does what its comments says
        public static class StringExtensions
        {
            /// <summary>
            /// takes a substring between two anchor strings (or the end of the string if that anchor is null)
            /// </summary>
            /// <param name="this">a string</param>
            /// <param name="from">an optional string to search after</param>
            /// <param name="until">an optional string to search before</param>
            /// <param name="comparison">an optional comparison for the search</param>
            /// <returns>a substring based on the search</returns>
            public static string Substring(this string @this, string from = null, string until = null, StringComparison comparison = StringComparison.InvariantCulture)
            {
                var fromLength = (from ?? string.Empty).Length;
                var startIndex = !string.IsNullOrEmpty(from)
                    ? @this.IndexOf(from, comparison) + fromLength
                    : 0;

                if (startIndex < fromLength) { throw new ArgumentException("from: Failed to find an instance of the first anchor"); }

                var endIndex = !string.IsNullOrEmpty(until)
                ? @this.IndexOf(until, startIndex, comparison)
                : @this.Length;

                if (endIndex < 0) { throw new ArgumentException("until: Failed to find an instance of the last anchor"); }

                var subString = @this.Substring(startIndex, endIndex - startIndex);
                return subString;
            }
        }