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'm not the first time here with questions like this.
I have a Volvo auto parts catalog that is implemented as a client application to a local database and works only in IE8/9. I need to find and get some positions displayed in IE.
Here's an example of IE output:
It's just a table and nothing more.
And here's what I see in IE9 debug tools:
IE shows me full layout of a page where I can see a target table and rows with the data I need to get.
I wrote a simple class that should walk through all IE tabs and get HTML from the target page:
using System.Globalization;
using System.Text.RegularExpressions;
using SHDocVw;
namespace WebpageHtmlMiner
{
static class HtmlMiner
{
public static string GetWebpageHtml(string uriPattern)
{
var uriRegexPattern = uriPattern;
var regex = new Regex(uriRegexPattern);
var shellWindows = new ShellWindows();
InternetExplorer internetExplorer = null;
foreach (InternetExplorer ie in shellWindows)
{
Match match = regex.Match(ie.LocationURL);
if (!string.IsNullOrEmpty(match.Value))
{
internetExplorer = ie;
break;
}
}
if (internetExplorer == null)
{
return "Target page is not opened in IE";
}
var mshtmlDocument = (mshtml.IHTMLDocument2)internetExplorer.Document;
var webpageHtml = mshtmlDocument.body.parentElement.outerHTML.ToString(CultureInfo.InvariantCulture);
return webpageHtml; //profit
}
}
}
It seems to work fine but instead of what I see in IE debug tools I get HTML code with tons of javascript functions and no data in target table.
Is there any way to get exactly what I see in IE debug tools?
Thanks.
You can get the original source (the one sent by the server) in "Script" tab (this works both on my IE8 and my IE10).
If you do not use AJAX, I think you can right-click on the page and choose Display Souce option too.
I have a dashboard which starts in a blank/default state. I am giving the user the ability to load a saved state into the dashboard. When they click the 'Apply' button I run the following code:
function CloseAndSave() {
var radUpload = $find(radUpload1ID);
var inputs = radUpload.getFileInputs();
if (inputs[0].value.length == 0) {
alert('Please select a dashboard to upload.');
return;
}
if( !radUpload.isExtensionValid(inputs[0].value) ) {
alert('Please select an XML file.');
radUpload.clearFileInputAt(0);
return;
}
oWindow = null;
__doPostBack(radButton1ID);
}
protected void RadButton1_Click(object sender, EventArgs e)
{
if (RadUpload1.UploadedFiles.Count > 0)
{
UploadedFile dashboardXMLFile = RadUpload1.UploadedFiles[0];
SerializableDictionary<string, string> dataToLoad = new SerializableDictionary<string, string>();
XmlSerializer xmlSerializer = new XmlSerializer(dataToLoad.GetType());
using (StreamReader reader = new StreamReader(dashboardXMLFile.InputStream))
{
dataToLoad = (SerializableDictionary<string, string>)xmlSerializer.Deserialize(reader);
}
foreach (var entry in dataToLoad)
{
string sessionKey = entry.Key;
if (!string.IsNullOrEmpty(entry.Value))
{
Type type = StateManager.GetTypeFromStateName(sessionKey);
byte[] data = Convert.FromBase64String(entry.Value);
using (MemoryStream memoryStream = new MemoryStream(data))
{
xmlSerializer = new XmlSerializer(type);
SessionRepository.Instance.SetSession(sessionKey, xmlSerializer.Deserialize(memoryStream));
}
}
}
}
}
RadButton1 has the property "AutoPostBack" set to false. I have set AutoPostBack to false because I wanted to perform validation before running the click event. So, now, I perform client-side validation and then allow the button click to run.
There's no update panel wrapping RadButton1. As such, the whole page posts after RadButton1_Click. This causes the state of the page to 'load up' the parsed state.
At this point, if I refresh the page, Google Chrome says "Please confirm form resubmission." I've read about how to squelch this, but I'd rather track down root cause.
Solution:
//This changes the response to a GET instead of a POST. Prevents the 'Form Resubmission' dialog.
Page.Response.Redirect(Page.Request.Url.ToString(), true);
When you refresh the browser, it will resend the last request you did. If it was a POST request (like you do in case of postback) then it will re-post the information but before doing it you'll see the warning message you describe.
The best way to avoid this problem is implementing the pattern Post/Redirect/Get
Post/Redirect/Get (PRG) is a common design pattern for web developers to help avoid certain duplicate form submissions and allow user agents to behave more intuitively with bookmarks and the refresh button.
Normally people don't implement this (although we should) unless the re-post may cause some data inconsistency.
When you refresh the browser, it will resend the last request you did. If it was a POST request (like you do in case of postback) then it will re-post the information but before doing it you'll see the warning message you describe.
Good day
I have question about displaying html documents in a windows forms applications. App that I'm working on should display information from the
database in the html format. I will try to describe actions that I have taken (and which failed):
1) I tried to load "virtual" html page that exists only in memory and dynamically change it's parameters (webbMain is a WebBrowser control):
public static string CreateBookHtml()
{
StringBuilder sb = new StringBuilder();
//Declaration
sb.AppendLine(#"<?xml version=""1.0"" encoding=""utf-8""?>");
sb.AppendLine(#"<?xml-stylesheet type=""text/css"" href=""style.css""?>");
sb.AppendLine(#"<!DOCTYPE html PUBLIC ""-//W3C//DTD XHTML 1.1//EN""
""http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"">");
sb.AppendLine(#"<html xmlns=""http://www.w3.org/1999/xhtml"" xml:lang=""en"">");
//Head
sb.AppendLine(#"<head>");
sb.AppendLine(#"<title>Exemplary document</title>");
sb.AppendLine(#"<meta http-equiv=""Content-Type"" content=""application/xhtml+xml;
charset=utf-8""/ >");
sb.AppendLine(#"</head>");
//Body
sb.AppendLine(#"<body>");
sb.AppendLine(#"<p id=""paragraph"">Example.</p>");
sb.AppendLine(#"</body>");
sb.AppendLine(#"</html>");
return sb.ToString();
}
void LoadBrowser()
{
this.webbMain.Navigate("about:blank");
this.webbMain.DocumentText = CreateBookHtml();
HtmlDocument doc = this.webbMain.Document;
}
This failed, because doc.Body is null, and doc.getElementById("paragraph") returns null too. So I cannot change paragraph InnerText property.
Furthermore, this.webbMain.DocumentText is "\0"...
2) I tried to create html file in specified folder, load it to the WebBrowser and then change its parameters. Html is the same as created by
CreateBookHtml() method:
private void LoadBrowser()
{
this.webbMain.Navigate("HTML\\BookPage.html"));
HtmlDocument doc = this.webbMain.Document;
}
This time this.webbMain.DocumentText contains Html data read from the file, but doc.Body returns null again, and I still cannot take element using
getByElementId() method. Of course, when I have text, I would try regex to get specified fields, or maybe do other tricks to achieve a goal, but I wonder - is there simply way to mainipulate html? For me, ideal way would be to create HTML text in memory, load it into the WebBrowser control, and then dynamically change its parameters using IDs. Is it possible? Thanks for the answers in advance, best regards,
Paweł
I've worked some time ago with the WebControl and like you wanted to load a html from memory but have the same problem, body being null. After some investigation, I noticed that the Navigate and NavigateToString methods work asynchronously, so it needs a little time for the control to load the document, the document is not available right after the call to Navigate. So i did something like (wbChat is the WebBrowser control):
wbChat.NavigateToString("<html><body><div>first line</div></body><html>");
DoEvents();
where DoEvents() is implemeted as:
[SecurityPermissionAttribute(SecurityAction.Demand, Flags = SecurityPermissionFlag.UnmanagedCode)]
public void DoEvents()
{
DispatcherFrame frame = new DispatcherFrame();
Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.Background,
new DispatcherOperationCallback(ExitFrame), frame);
Dispatcher.PushFrame(frame);
}
and it worked for me, after the DoEvents call, I could obtain a non-null body:
mshtml.IHTMLDocument2 doc2 = (mshtml.IHTMLDocument2)wbChat.Document;
mshtml.HTMLDivElement div = (mshtml.HTMLDivElement)doc2.createElement("div");
div.innerHTML = "some text";
mshtml.HTMLBodyClass body = (mshtml.HTMLBodyClass)doc2.body;
if (body != null)
{
body.appendChild((mshtml.IHTMLDOMNode)div);
body.scrollTop = body.scrollHeight;
}
else
Console.WriteLine("body is still null");
I don't know if this is the right way of doing this, but it fixed the problem for me, maybe it helps you too.
Later Edit:
public object ExitFrame(object f)
{
((DispatcherFrame)f).Continue = false;
return null;
}
The DoEvents method is necessary on WPF. For System.Windows.Forms one can use Application.DoEvents().
Another way to do the same thing is:
webBrowser1.DocumentText = "<html><body>blabla<hr/>yadayada</body></html>";
this works without any extra initialization
I am using the SharePoint Object Model via a console app on the same server as the SharePoint installation, and using the following code:
SPSite MySite = new SPSite("http://server/");
SPWeb MyWeb = MySite.OpenWeb();
MyWeb.AllowUnsafeUpdates = true;
SPList MyList = MyWeb.Lists["Test"];
const string EmptyQuery = "0";
SPQuery q = new SPQuery { Query = EmptyQuery };
String Source = "Test String";
for( int i = 1; i < 1000; i++)
{
Console.WriteLine("Creating new item");
SPListItem MyItem = MyList.GetItems(q).Add();
Console.WriteLine("Created new item");
Console.WriteLine("Assigning Title Value");
MyItem["Title"] = Source.ToString();
Console.WriteLine("Assigned Title Value");
MyItem.Update();
}
I am getting a several second pause between "Assigning Title Value" and "Assigned Title Value".
When I deploy the code as a Web Part, its instantaneous, the delay only seems to be when the code is deployed as a console application.
Edit: More information! When I have more than one field being assigned, its always the first field that is slow, any subsequent assignments are as fast as expected. If I switch the order of fields around, it has no effect on the delay - the first field is always slow.
Any thoughts?
It looks like this is because you're not accessing any fields before using the setter. If you read at least one field first, you'd probably see a slight delay there, and no delay on the setter, because under the hood SetValue() calls EnsureFieldCollection(), which - if the fields for the list item haven't already been populated - has to check back to the SPList's fields collection.
Also, this is not in your code snippet, but make sure you are disposing of your SPWeb and SPSite objects when you're done. A good pattern is to use using:
using(SPSite site = new SPSite("url"))
{
using(SPWeb web = site.OpenWeb())
{
//do stuff
}
}
First of all I would suggest making use of
using (SPSite MySite = new SPSite("http://server/"))
{
using (SPWeb MyWeb = MySite.OpenWeb())
{
//do your stuff here
}
}
You can check the EnsureFieldCollection by reading all the fields of the item before updating the field. If after that your first field is updated instantly you can be pretty sure that that is the reason.
It may be a difference between Release and Debug builds, or the fact it has the debugger attatched. Try changing to a Release build, and if that doesn't work try running it without the debugger (Ctrl+F5 in Visual Studio)