I need to scrape a table from a website with C# and export the data into pgadmin as a database that would store the data for usage later on. I´ve tried to use different methods that I have seen on the internet and the "await" method seems to be the best way according to others. I have not found any example of its usage and therefore the following code is what I have come up with. (I use windows forms in visual studio)
string url = ("internet website here");
WebClient webclient = new WebClient();
string page = webclient.DownloadString(url);
HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
doc.LoadHtml(page);
List<List<string>> table = doc.DocumentNode.SelectNodes("//*[#id=\"cr_cashflow\"]/div[2]/div/table")
.Descendants("tr")
.Where(tr=>tr.Elements("td").Count() > 0)
.Select(tr => tr.Elements("td").Select(td => td.InnerText.Trim()).ToList())
.ToList();dataGridTable1.Datasource=table
The internet xpath is the following that I want to scrape:
<table class='cr_dataTable>
<tbody>
<tr classs>
<td class>Values</td>
<td class>1,356</td>
<td class>1,256</td>
<td class>1,459</td>
<td class>1,535</td>
What I have is to copy the xpath of the table "cr_dataTable".
Now to the problem, as I'm new to the programming world I'm still learning how this method works and the code tells me:
"System.NullReferenceException: 'Object reference not set to an instance of an object.'
HtmlAgilityPack.HtmlNode.SelectNodes(...) returned null."
How should I think about the usage of this method to find the values of "cr_dataTable" without getting the return null message? At this point I dont know what i´m missing for the code to work. Thankful if someone knows thats wrong in the code and how to make it work.
According to your reply, I wrote new code. You can refer to this.
What I want to emphasize is that table."SelectNodes(".//tr")" can parse all the "tr" information under this table. And "table.SelectNodes("//tr")" gets all the "tr" of the current html, if there are two tables, it will get all the "tr" information of the two tables. Which one to use depends on the situation.
Code show as below:
var url = #”html://111.com”;
var web = new HtmlWeb();
web.Load(url);
HtmlDocument doc = new HtmlDocument();
doc.LoadHtml("//*[#id=\"cr_cashflow\"]/div[2]/div/table");
foreach (HtmlNode table in doc.DocumentNode.SelectNodes("//table"))
{
foreach (HtmlNode row in table.SelectNodes("tr"))
{
Console.WriteLine("row");
foreach (HtmlNode cell in row.SelectNodes("th|td"))
{
Console.WriteLine("cell:" + cell.InnerText);
}
}
}
This is probably a very simple problem, but I am extremely new to C# / MVC and I have been handed a broken project to fix. So it's time to sink or swim!
I have an array of strings that is being passed from a function to the front end.
The array looks something like
reports = Directory.GetFiles(#"~\Reports\");
On the front end, I would like it to display each report, but I am not sure how to do that.
This project is using a MVC, and I believe the view is called "Razor View"? I know that it's using an HTML helper.
In essence, I need something like
#HTML.DisplayTextFor(Model.report [And then print every report in the array]);
I hope that makes sense.
If you want to display the file name array you can simply use a foreach:
#foreach(var report in Model.Reports){ #report }
Note that you should add the Reports property to your view model:
public class SampleViewModel
{
public string [] Reports { get; set; }
}
You could use ViewData or TempData but I find that using the view model is the better way.
You can then populate it:
[HttpGet]
public ActionResult Index()
{
var model = new SampleViewModel(){ Reports = Directory.GetFiles(#"~\Reports\")};
return View(model);
}
And use it in the view as you see fit.
Here is a simple online example: https://dotnetfiddle.net/5WmX5M
If you'd like to add a null check at the view level you can:
#if(Model.Reports != null)
{
foreach(var report in Model.Reports){ #report <br> }
}
else
{
<span> No files found </span>
}
https://dotnetfiddle.net/melMLW
This is never a bad idea, although in this case GetFiles will return an empty list if no files can be found, and I assume a possible IOException is being handled.
Hallo guys!
Sorry for the dump question, this is my last resort. I swear i triend countless of other Stackoverflow questions, different Frameworks, etc., but those didnt seem to help.
Ich have the following Problem:
A website displays a list of data (there is a TON of div, li, span etc. tags infront, its a big HTML.)
Im writing a tool that fetches data from a specific list inside a ton of other div tags, downloads it and outputs an excel file.
The website im trying to access, is dynamic. So you open the website, it loads a little bit, and then the list appears (probably some JS and stuff).
When i try to download the website via a webRequest in C#, the html I get ist almost empty with a ton on white spaces, lots of non-html stuff, some garbage data as well.
Now: Im pretty used to C#, HTMLAgillityPack, and countless other libraries, not so much in web related stuff tho. I tried CefSharp, Chromium etc. all of those stuff, but couldnt get them to work properly unfortunately.
I want to have a HTML in my program to work with that looks exactly like the HTML that you see when
you open the dev console in chrome wenn visting the website mentined above.
The HTML parser works flwalessly there.
This is how I image how the code could look like simplified.
Extreme C# pseudocode:
WebBrowserEngine web = new WebBrowserEngine()
web.LoadURLuntilFinished(url); // with all the JS executed and stuff
String html = web.getHTML();
web.close();
My Goal would be that the string html in the pseudocode looks exactly like the one in the Chrome dev tab.
Maybe there is a solution posted somewhere else but i swear i coudlnt find it, been looking for days.
Andy help is greatly appreciated.
#SpencerBench is spot on in saying
It could be that the page is using some combination of scroll state, element visibility, or element positions to trigger content loading. If that's the case, then you'll need to figure out what it is and trigger it programmatically.
To answer the question for your specific use case, we need to understand the behaviour of the page you want to scrape data from, or as I asked in the comments, how do you know the page is "finished"?
However, it's possible to give a fairly generic answer to the question which should act as a starting point for you.
This answer uses Selenium, a package which is commonly used for automating testing of web UIs, but as they say on their home page, that's not the only thing it can be used for.
Primarily it is for automating web applications for testing purposes, but is certainly not limited to just that. Boring web-based administration tasks can (and should) also be automated as well.
The web site I'm scraping
So first we need a web site. I've created one using ASP.net core MVC with .net core 3.1, although the web site's technology stack isn't important, it's the behaviour of the page you want to scrape which is important. This site has 2 pages, unimaginatively called Page1 and Page2.
Page controllers
There's nothing special in these controllers:
namespace StackOverflow68925623Website.Controllers
{
using Microsoft.AspNetCore.Mvc;
public class Page1Controller : Controller
{
public IActionResult Index()
{
return View("Page1");
}
}
}
namespace StackOverflow68925623Website.Controllers
{
using Microsoft.AspNetCore.Mvc;
public class Page2Controller : Controller
{
public IActionResult Index()
{
return View("Page2");
}
}
}
API controller
There's also an API controller (i.e. it returns data rather than a view) which the views can call asynchronously to get some data to display. This one just creates an array of the requested number of random strings.
namespace StackOverflow68925623Website.Controllers
{
using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Text;
[Route("api/[controller]")]
[ApiController]
public class DataController : ControllerBase
{
[HttpGet("Create")]
public IActionResult Create(int numberOfElements)
{
var response = new List<string>();
for (var i = 0; i < numberOfElements; i++)
{
response.Add(RandomString(10));
}
return Ok(response);
}
private string RandomString(int length)
{
var sb = new StringBuilder();
var random = new Random();
for (var i = 0; i < length; i++)
{
var characterCode = random.Next(65, 90); // A-Z
sb.Append((char)characterCode);
}
return sb.ToString();
}
}
}
Views
Page1's view looks like this:
#{
ViewData["Title"] = "Page 1";
}
<div class="text-center">
<div id="list" />
<script src="~/lib/jquery/dist/jquery.min.js"></script>
<script>
var apiUrl = 'https://localhost:44394/api/Data/Create';
$(document).ready(function () {
$('#list').append('<li id="loading">Loading...</li>');
$.ajax({
url: apiUrl + '?numberOfElements=20000',
datatype: 'json',
success: function (data) {
$('#loading').remove();
var insert = ''
for (var item of data) {
insert += '<li>' + item + '</li>';
}
insert = '<ul id="results">' + insert + '</ul>';
$('#list').html(insert);
},
error: function (xht, status) {
alert('Error: ' + status);
}
});
});
</script>
</div>
So when the page first loads, it just contains an empty div called list, however the page loading trigger's the function passed to jQuery's $(document).ready function, which makes an asynchronous call to the API controller, requesting an array of 20,000 elements. While the call is in progress, "Loading..." is displayed on the screen, and when the call returns, this is replaced by an unordered list containing the received data. This is written in a way intended to be friendly to developers of automated UI tests, or of screen scrapers, because we can tell whether all the data has loaded by testing whether or not the page contains an element with the ID results.
Page2's view looks like this:
#{
ViewData["Title"] = "Page 2";
}
<div class="text-center">
<div id="list">
<ul id="results" />
</div>
<script src="~/lib/jquery/dist/jquery.min.js"></script>
<script>
var apiUrl = 'https://localhost:44394/api/Data/Create';
var requestCount = 0;
var maxRequests = 20;
$(document).ready(function () {
getData();
});
function getDataIfAtBottomOfPage() {
console.log("scroll - " + requestCount + " requests");
if (requestCount < maxRequests) {
console.log("scrollTop " + document.documentElement.scrollTop + " scrollHeight " + document.documentElement.scrollHeight);
if (document.documentElement.scrollTop > (document.documentElement.scrollHeight - window.innerHeight - 100)) {
getData();
}
}
}
function getData() {
window.onscroll = undefined;
requestCount++;
$('results2').append('<li id="loading">Loading...</li>');
$.ajax({
url: apiUrl + '?numberOfElements=50',
datatype: 'json',
success: function (data) {
var insert = ''
for (var item of data) {
insert += '<li>' + item + '</li>';
}
$('#loading').remove();
$('#results').append(insert);
if (requestCount < maxRequests) {
window.setTimeout(function () { window.onscroll = getDataIfAtBottomOfPage }, 1000);
} else {
$('#results').append('<li>That\'s all folks');
}
},
error: function (xht, status) {
alert('Error: ' + status);
}
});
}
</script>
</div>
This gives a nicer user experience because it requests data from the API controller in multiple smaller chunks, so the first chunk of data appears fairly quickly, and once the user has scrolled down to somewhere near the bottom of the page, the next chunk of data is requested, until 20 chunks have been requested and displayed, at which point the text "That's all folks" is added to the end of the unordered list. However this is more difficult to interact with programmatically because you need to scroll the page down to make the new data appear.
(Yes, this implementation is a bit buggy - if the user gets to the bottom of the page too quickly then requesting the next chunk of data doesn't happen until they scroll up a bit. But the question isn't about how to implement this behaviour in a web page, but about how to scrape the displayed data, so please forgive my bugs.)
The scraper
I've implemented the scraper as a xUnit unit test project, just because I'm not doing anything with the data I've scraped from the web site other than Asserting that it is of the correct length, and therefore proving that I haven't prematurely assumed that the web page I'm scraping from is "finished". You can put most of this code (other than the Asserts) into any type of project.
Having created your scraper project, you need to add the Selenium.WebDriver and Selenium.WebDriver.ChromeDriver nuget packages.
Page Object Model
I'm using the Page Object Model pattern to provide a layer of abstraction between functional interaction with the page and the implementation detail of how to code that interaction. Each of the pages in the web site has a corresponding page model class for interacting with that page.
First, a base class with some code which is common to more than one page model class.
namespace StackOverflow68925623Scraper
{
using System;
using OpenQA.Selenium;
using OpenQA.Selenium.Support.UI;
public class PageModel
{
protected PageModel(IWebDriver driver)
{
this.Driver = driver;
}
protected IWebDriver Driver { get; }
public void ScrollToTop()
{
var js = (IJavaScriptExecutor)this.Driver;
js.ExecuteScript("window.scrollTo(0, 0)");
}
public void ScrollToBottom()
{
var js = (IJavaScriptExecutor)this.Driver;
js.ExecuteScript("window.scrollTo(0, document.body.scrollHeight)");
}
protected IWebElement GetById(string id)
{
try
{
return this.Driver.FindElement(By.Id(id));
}
catch (NoSuchElementException)
{
return null;
}
}
protected IWebElement AwaitGetById(string id)
{
var wait = new WebDriverWait(Driver, TimeSpan.FromSeconds(10));
return wait.Until(e => e.FindElement(By.Id(id)));
}
}
}
This base class gives us 4 convenience methods:
Scroll to the top of the page
Scroll to the bottom of the page
Get the element with the supplied ID, or return null if it doesn't exist
Get the element with the supplied ID, or wait for up to 10 seconds for it to appear if it doesn't exist yet
And each page in the web site has its own model class, derived from that base class.
namespace StackOverflow68925623Scraper
{
using OpenQA.Selenium;
public class Page1Model : PageModel
{
public Page1Model(IWebDriver driver) : base(driver)
{
}
public IWebElement AwaitResults => this.AwaitGetById("results");
public void Navigate()
{
this.Driver.Navigate().GoToUrl("https://localhost:44394/Page1");
}
}
}
namespace StackOverflow68925623Scraper
{
using OpenQA.Selenium;
public class Page2Model : PageModel
{
public Page2Model(IWebDriver driver) : base(driver)
{
}
public IWebElement Results => this.GetById("results");
public void Navigate()
{
this.Driver.Navigate().GoToUrl("https://localhost:44394/Page2");
}
}
}
And the Scraper class:
namespace StackOverflow68925623Scraper
{
using OpenQA.Selenium.Chrome;
using System;
using System.Threading;
using Xunit;
public class Scraper
{
[Fact]
public void TestPage1()
{
// Arrange
var driver = new ChromeDriver();
var page = new Page1Model(driver);
page.Navigate();
try
{
// Act
var actualResults = page.AwaitResults.Text.Split(Environment.NewLine);
// Assert
Assert.Equal(20000, actualResults.Length);
}
finally
{
// Ensure the browser window closes even if things go pear-shaped
driver.Quit();
}
}
[Fact]
public void TestPage2()
{
// Arrange
var driver = new ChromeDriver();
var page = new Page2Model(driver);
page.Navigate();
try
{
// Act
while (!page.Results.Text.Contains("That's all folks"))
{
Thread.Sleep(1000);
page.ScrollToBottom();
page.ScrollToTop();
}
var actualResults = page.Results.Text.Split(Environment.NewLine);
// Assert - we expect 1001 because of the extra "that's all folks"
Assert.Equal(1001, actualResults.Length);
}
finally
{
// Ensure the browser window closes even if things go pear-shaped
driver.Quit();
}
}
}
}
So, what's happening here?
// Arrange
var driver = new ChromeDriver();
var page = new Page1Model(driver);
page.Navigate();
ChromeDriver is in the Selenium.WebDriver.ChromeDriver package and implements the IWebDriver interface from the Selenium.WebDriver package with the code to interact with the Chrome browser. Other packages are available containing implementations for all popular browsers. Instantiating the driver object opens a browser window, and calling its Navigate method directs the browser to the page we want to test/scrape.
// Act
var actualResults = page.AwaitResults.Text.Split(Environment.NewLine);
Because on Page1, the results element doesn't exist until all the data has been displayed, and no user interaction is required in order for it to be displayed, we use the page model's AwaitResults property to just wait for that element to appear and return it once it has appeared.
AwaitResults returns an IWebElement instance representing the element, which in turn has various methods and properties we can use to interact with the element. In this case we use its Text property which returns the element's contents as a string, without any markup. Because the data is displayed as an unordered list, each element in the list is delimited by a line break, so we can can use String's Split method to convert it to a string array.
Page2 needs a different approach - we can't use the presence of the results element to determine whether the data has all been displayed, because that element is on the page right from the start, instead we need to check for the string "That's all folks" which is written right at the end of the last chunk of data. Also the data isn't loaded all in one go, and we need to keep scrolling down in order to trigger the loading of the next chunk of data.
// Act
while (!page.Results.Text.Contains("That's all folks"))
{
Thread.Sleep(1000);
page.ScrollToBottom();
page.ScrollToTop();
}
var actualResults = page.Results.Text.Split(Environment.NewLine);
Because of the bug in the UI that I mentioned earlier, if we get to the bottom of the page too quickly, the fetch of the next chunk of data isn't triggered, and attempting to scroll down when already at the bottom of the page doesn't raise another scroll event. That's why I'm scrolling to the bottom of the page and then back to the top - that way I can guarantee that a scroll event is raised. You never know, the web site you're trying to scrape data from may itself be buggy.
Once the "That's all folks" text has appeared, we can go ahead and get the results element's Text property and convert it to a string array as before.
// Assert - we expect 1001 because of the extra "that's all folks"
Assert.Equal(1001, actualResults.Length);
This is the bit that won't be in your code. Because I'm scraping a web site which is under my control, I know exactly how much data it should be displaying so I can check that I've got all the data, and therefore that my scraping code is working correctly.
Further reading
Absolute beginner's introduction to Selenium: https://www.guru99.com/selenium-csharp-tutorial.html
(A curiosity in that article is the way that it starts by creating a console application project and later changes its output type to class library and manually adds the unit test packages, when the project could have been created using one of Visual Studio's unit test project templates. It gets to the right place in the end, albeit via a rather odd route.)
Selenium documentation: https://www.selenium.dev/documentation/
Happy scraping!
If you need to fully execute the web page, then a complete browser like CefSharp is your only option.
It could be that the page is using some combination of scroll state, element visibility, or element positions to trigger content loading. If that's the case, then you'll need to figure out what it is and trigger it programmatically. I know that CefSharp can simulate user actions like clicking, scrolling, etc.
I've been trying, without luck, to use IJavaScriptExecutor to find a specific header string in a page. Here's the html code form the page:
<div class="wrap">
<h2>Edit Page <a href="http://www.webtest.bugrit.net/wordpress/wp-admin/post-
new.php?post_type=page" class="add-new-h2">Add New</a></h2>
<div id...
The text I need to check for is the "Edit Page" string.
This is the closest I've come, which isn't very close:
var element = FFDriver.Instance.FindElements(By.ClassName("add-new-h2"));
IJavaScriptExecutor js = FFDriver.Instance as IJavaScriptExecutor;
if (js != null) {
string innerHtml = (string)js.ExecuteScript("return arguments[0].innerHTML;", element);
//System.Windows.Forms.MessageBox.Show(innerHtml);
if (innerHtml.Equals("Edit Page")) {
return true;
} else {
return false;
}
}
Now, I realize that the text I should expect to get from that code isn't the exact string "Edit Page". But shouldn't it return something? When I enable the MessageBox line, the innerHtml string is empty.
Or, of couse - if someone knows another, possible easier, way to check for the existance of a specific string inside a specific html tag, I'm all ears.
Your element returns you <a> element, not <h2>. Your <a> doesn't contain Edit Page string.
Try find your element like this to the parent element <h2> (only if class name add-new-h2 is unique, otherwise you will get the first matching one):
var element = FFDriver.Instance.FindElement(By.XPath(".//a[#class='add-new-h2']/.."));
var containsText = element.Text.Contains("Edit Page");
I am trying to write an application to automate router configuration. Unfortunately with the router we are using, telnet is not an option.
So I have had to interface with the Cisco web interface using C# WebClient class.
Up until now I had been able to set everything I needed using NameValueCollection and WebClient.UploadValues.
I would take all the input elements on the form, then just upload the name value Collection corresponding to the input types on the form, setting the values of each to the desired setting.
But now I have run into a problem.
With one of the forms, it is using a multiselect control to handle an array of input data, not an input type.
I am at a total loss for how to set this.
The html for the multiselect is as follows
<select multiple class="MultiSelect" name="PortRangeList" size="12" onChange="showList(this.form.PortRangeList);" style="width: 100%">
<option value="All Traffic{[(*-*-*)]}1;0;1;65535;0}">All Traffic [TCP&UDP/1~65535]</option>
<option value="DNS{[(*-*-*)]}2;17;53;53;0}">DNS [UDP/53~53]</option>
<option value="FTP{[(*-*-*)]}3;6;21;21;0}">FTP [TCP/21~21]</option>
...
</select>
When I was using the input types, I would simply do the following
NameValueCollection formNetworkData = new NameValueCollection();
formNetworkData["ipAddr"] = "192.168.1.2";
formNetworkData["lanMask"] = "255.255.255.0";
downloadedData = _routerWebClient.UploadValues(_routerIP + NETWORK, formNetworkData);
But looking at the code for this new form, it appears right before it submits, it selects all the options in the multiselect.
I realize I have probably asked this question poorely, but any assistance would be greatly appreciated.
Using Chrome debugger PortRangeList is exactly as you said.
There are 5 input types
submitStatus, upnpOpen (etc...)
For those my code looks like this
NameValueCollection formData = new NameValueCollection();
formData["submitStatus"]="1";
formData["upnpOpen"]="0";
downloadedData = _routerWebClient.UploadValues(SERVICE0, formData);
But in order to submit the PortRangeList data, I can't use the NameValueCollection because it does not allow a name to have muliple values.
how could submit that?
WebClient.UploadData, WebClient.UploadFile or WebClient.UploadString maybe?
Use Fiddler or Wireshark to compare what goes over the wire when it works ("normal" browser) and when it doesn't work (your code)... once you know the differences you can change your code accordingly...
You have to pass in the selected options by passing in the "PortRangeList" parameter multiple times, once for each option:
PortRangeList=All Traffic{[(*-*-*)]}1;0;1;65535;0}&PortRangeList=DNS{[(*-*-*)]}2;17;53;53;0}&PortRangeList=FTP{[(*-*-*)]}3;6;21;21;0}
That's how browsers do it. Since you're using the WebClient, try this:
PortRangeList=All Traffic{[(*-*-*)]}1;0;1;65535;0},DNS{[(*-*-*)]}2;17;53;53;0},FTP{[(*-*-*)]}3;6;21;21;0}
Obviously, everything has to be properly URL-escaped.
Thought I would post the final answer.
In the end I used the exact solution shown here.
http://anhonga.wordpress.com/2010/05/06/using-webclient-with-uploadvalues-and-uploadstring-to-simulate-post/
This is with his code, but I did essentially the exact same thing (without using global variables)
StringBuilder _strBld = new StringBuilder();
int _intItemCount = 0;
protected void btnSubmit_Click(object sender, EventArgs e)
{
System.Net.WebClient myWebClient = new System.Net.WebClient();
myWebClient.Headers.Add("Charset", "text/html; charset=UTF-8");
myWebClient.Headers.Add("Content-Type", "application/x-www-form-urlencoded"); // ◄ This line is essential
// Perform server-side validations (same as before)
if (this.F_Name.Text.Length == 0 || this.L_Name.Text.Length == 0)
{ AppendError("First and Last name must be provided"); }
…
// Add the user-provided name values
AppendUploadString("last_name", this.L_Name.Text);
AppendUploadString ("first_name", this.F_Name.Text);
AppendUploadString ("address", this.Address.Text);
// Add the Toppings
foreach (ListItem item in this.ToppingsChkBoxList.Items)
{
if (item.Selected)
{
AppendUploadString("Toppings", item.Value.ToString());
}
}
myWebClient.UploadString("https http://www.Destination.com/...?encoding=UTF-8", "POST", _strBld.ToString());
}
private void AppendUploadString(string strName, string strValue)
{
_intItemCount++;
_strBld.Append((intItemCount == 1 ? "" : "&") + strName + "=" + System.Web.HttpUtility.UrlEncode(strValue));
// Update: Use UrlEncode to ensure that the special characters are included in the submission
}