此代码运行正常：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
using System.Net;
using System.Dynamic;
using HtmlAgilityPack;
namespace entropedizer
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public String postRequest(string url, string eventTarget)
{
// A "pre-request," sent to gather SessionID and POST data parameters for the main request
HttpWebRequest prequest = (HttpWebRequest)WebRequest.Create("http://www.entropedia.info/Chart.aspx?chart=Chart");
HttpWebResponse presponse = (HttpWebResponse)prequest.GetResponse();
Stream pstream = presponse.GetResponseStream();
StreamReader psr = new StreamReader(pstream);
string phtml = psr.ReadToEnd();
Match viewstate = Regex.Match(phtml, "id=\"__VIEWSTATE\".+/>");
Match eventvalidation = Regex.Match(phtml, "id=\"__EVENTVALIDATION\".+/>");
ASCIIEncoding encoding = new ASCIIEncoding();
string postData = "__EVENTTARGET=" + eventTarget + "&__VIEWSTATE=" + Uri.EscapeDataString(viewstate.ToString().Substring(24, viewstate.Length - 28)) + "&__EVENTVALIDATION=" + Uri.EscapeDataString(eventvalidation.ToString().Substring(30, eventvalidation.Length - 34));
byte[] data = encoding.GetBytes(postData);
// The main request, intended to retreive the desired HTML
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.entropedia.info/Chart.aspx?chart=Chart");
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.CookieContainer = new CookieContainer();
Cookie sessionId = new Cookie("ASP.NET_SessionId", Regex.Match(presponse.Headers.ToString(), "ASP.NET_SessionId=.+ d").ToString().Substring(18, Regex.Match(presponse.Headers.ToString(), "ASP.NET_SessionId=.+ d").Length - 21), "/", ".entropedia.info");
request.CookieContainer.Add(new Uri("http://www.entropedia.info/Chart.aspx?chart=Chart"), sessionId);
Stream stream = request.GetRequestStream();
stream.Write(data, 0, data.Length);
stream.Close();
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
stream = response.GetResponseStream();
StreamReader sr = new StreamReader(stream);
return sr.ReadToEnd();
}
private void Form1_Load(object sender, EventArgs e)
{
System.Net.ServicePointManager.Expect100Continue = false;
HtmlAgilityPack.HtmlDocument hChart = new HtmlAgilityPack.HtmlDocument();
hChart.LoadHtml(postRequest("http://www.entropedia.info/Chart.aspx?chart=Chart", "ctl00%24ContentPlaceHolder1%24DG1%24ctl19%24ctl05"));
HtmlNodeCollection chartStrings = hChart.DocumentNode.SelectNodes("/html/body/form");
CheckedListBox chartOptions = new CheckedListBox();
foreach (HtmlNode i in chartStrings)
{
chartOptions.Items.Add(chartStrings[i].ToString());
}
this.Controls.Add(chartOptions);
}
}
}
此代码生成运行时异常：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
using System.Net;
using System.Dynamic;
using HtmlAgilityPack;
namespace entropedizer
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public String postRequest(string url, string eventTarget)
{
// A "pre-request," sent to gather SessionID and POST data parameters for the main request
HttpWebRequest prequest = (HttpWebRequest)WebRequest.Create("http://www.entropedia.info/Chart.aspx?chart=Chart");
HttpWebResponse presponse = (HttpWebResponse)prequest.GetResponse();
Stream pstream = presponse.GetResponseStream();
StreamReader psr = new StreamReader(pstream);
string phtml = psr.ReadToEnd();
Match viewstate = Regex.Match(phtml, "id=\"__VIEWSTATE\".+/>");
Match eventvalidation = Regex.Match(phtml, "id=\"__EVENTVALIDATION\".+/>");
ASCIIEncoding encoding = new ASCIIEncoding();
string postData = "__EVENTTARGET=" + eventTarget + "&__VIEWSTATE=" + Uri.EscapeDataString(viewstate.ToString().Substring(24, viewstate.Length - 28)) + "&__EVENTVALIDATION=" + Uri.EscapeDataString(eventvalidation.ToString().Substring(30, eventvalidation.Length - 34));
byte[] data = encoding.GetBytes(postData);
// The main request, intended to retreive the desired HTML
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.entropedia.info/Chart.aspx?chart=Chart");
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.CookieContainer = new CookieContainer();
Cookie sessionId = new Cookie("ASP.NET_SessionId", Regex.Match(presponse.Headers.ToString(), "ASP.NET_SessionId=.+ d").ToString().Substring(18, Regex.Match(presponse.Headers.ToString(), "ASP.NET_SessionId=.+ d").Length - 21), "/", ".entropedia.info");
request.CookieContainer.Add(new Uri("http://www.entropedia.info/Chart.aspx?chart=Chart"), sessionId);
Stream stream = request.GetRequestStream();
stream.Write(data, 0, data.Length);
stream.Close();
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
stream = response.GetResponseStream();
StreamReader sr = new StreamReader(stream);
return sr.ReadToEnd();
}
private void Form1_Load(object sender, EventArgs e)
{
System.Net.ServicePointManager.Expect100Continue = false;
HtmlAgilityPack.HtmlDocument hChart = new HtmlAgilityPack.HtmlDocument();
hChart.LoadHtml(postRequest("http://www.entropedia.info/Chart.aspx?chart=Chart", "ctl00%24ContentPlaceHolder1%24DG1%24ctl19%24ctl05"));
HtmlNodeCollection chartStrings = hChart.DocumentNode.SelectNodes("/html/body/form/table");
CheckedListBox chartOptions = new CheckedListBox();
foreach (HtmlNode i in chartStrings)
{
chartOptions.Items.Add(chartStrings[i].ToString());
}
this.Controls.Add(chartOptions);
}
}
}
不同之处在于第 68 行。我只是试图在 HTML 中更深入地挖掘一层，这会导致 chartStrings 为空。
这是一个例外：
See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.
************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
at entropedizer.Form1.Form1_Load(Object sender, EventArgs e) in c:\Users\Admin\Documents\Visual Studio 2012\Projects\entropedizer\entropedizer\Form1.cs:line 71
at System.Windows.Forms.Form.OnLoad(EventArgs e)
at System.Windows.Forms.Form.OnCreateControl()
at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
at System.Windows.Forms.Control.CreateControl()
at System.Windows.Forms.Control.WmShowWindow(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
at System.Windows.Forms.ContainerControl.WndProc(Message& m)
at System.Windows.Forms.Form.WmShowWindow(Message& m)
at System.Windows.Forms.Form.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
************** Loaded Assemblies **************
mscorlib
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.18034 built by: FX45RTMGDR
CodeBase: file:///C:/Windows/Microsoft.NET/Framework/v4.0.30319/mscorlib.dll
----------------------------------------
entropedizer
Assembly Version: 1.0.0.0
Win32 Version: 1.0.0.0
CodeBase: file:///C:/Users/Admin/Documents/Visual%20Studio%202012/Projects/entropedizer/entropedizer/bin/Debug/entropedizer.exe
----------------------------------------
System.Windows.Forms
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.18036 built by: FX45RTMGDR
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Windows.Forms/v4.0_4.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System.Drawing
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.18021 built by: FX45RTMGDR
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Drawing/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
System
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.18034 built by: FX45RTMGDR
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System/v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
HtmlAgilityPack
Assembly Version: 1.4.6.0
Win32 Version: 1.4.6.0
CodeBase: file:///C:/Users/Admin/Documents/Visual%20Studio%202012/Projects/entropedizer/entropedizer/bin/Debug/HtmlAgilityPack.DLL
----------------------------------------
System.Xml
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.18034 built by: FX45RTMGDR
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Xml/v4.0_4.0.0.0__b77a5c561934e089/System.Xml.dll
----------------------------------------
System.Configuration
Assembly Version: 4.0.0.0
Win32 Version: 4.0.30319.17929 built by: FX45RTMREL
CodeBase: file:///C:/Windows/Microsoft.Net/assembly/GAC_MSIL/System.Configuration/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Configuration.dll
----------------------------------------
************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.
For example:
<configuration>
<system.windows.forms jitDebugging="true" />
</configuration>
When JIT debugging is enabled, any unhandled exception
will be sent to the JIT debugger registered on the computer
rather than be handled by this dialog box.
提前感谢您的帮助，非常感谢！