I'm working with the Webbrowser control in C# and trying to access some HtmlElements in the document.
The problem is that the document Body only contains two out of five children. (http://www.target.com/cart/ref=nav_sc_rev_checkout). So I can't access specific elements in the body, although it renders fine in the UI.
I suspect that there is bad HTML in the Body so that the Document Tree is corrupt?
Is there a way to handle this, since it still renders nice..?
Thanks.
Update:
The problem was that the DocumentCompleted event was triggered but the Doc was not fully parsed so that was why I only got 2 out of 5 elements.
Yes, the WebBrowser is a wrapper round IE and it will handle bad HTML as good as it can.
Can't you simply write the contents to a text file instead of a web browser control and make that into a HTML file. Then load it in your browser and inspect with the dev tool of your choice.
Beside the fact the html code of this site have more than 200 errors (mostly missing entities), you can try to load the code into an XmlDocument or XDocument inside your program and access the nodes you want via XPath.
If you need to programmatically interact with HTML and more specifically bad HTML I would suggest you to take a look at HTMLAgilityPack.
This is an agile HTML parser that
builds a read/write DOM and supports
plain XPATH or XSLT (you actually
don't HAVE to understand XPATH nor
XSLT to use it, don't worry...). It is
a .NET code library that allows you to
parse "out of the web" HTML files. The
parser is very tolerant with "real
world" malformed HTML. The object
model is very similar to what proposes
System.Xml, but for HTML documents (or
streams).
Related
I have made a web crawler by using Asp.net. It's work well. Problem is when I want to extract content from it. Some of content wrap by between HTML tags. I have some of solutions to extract content from it but I don't know which one are better. It should be good performance and easy to implement.
Using Regex with many patterns to extact content.
Using Linq to XML to extract content.
Using XPath to extract content.
Somebody please help me choose the better solutions. I think I will go with XPath but I am not sure about performance are better than RegEx or Linq2XML.
Many thanks for any ideas.
None of your solutions is particularly good.
HTML is not a regular language and as such is not a good fit for regular expressions. See also the standard response to parsing HTML with regex.
HTML is not necessarily valid XML
Instead, you should use a HTML parsing library like the Html Agility Pack.
Neither. Use a proper HTML parser such as HTML Agility Pack
RegEx is no doubt faster than both Linq to XML and XPath way. But you cannot parse everything out of the html markup using RegEx. Html is too complex for that purpose.
I didn't design my own Crawler though, I used arachnode.net, and it crawls massive amount of data. And everywhere I've used Html Agility Pack to extract various components i.e. Html Controls, Cookies, MetaTags etc etc.
As the other guys already hinted - use proper HTML parser. In most cases, HTML is not written good enough to be treated as XML. What's worse, HTML5 pushes for syntax that is completely non parseable. For example, HTML5 allows you to omit quotes around attributes.
Along with HTML Agility Pack, you can take a look at Majestic-12's HTML Parser: Majestic-12 : Projects : C# HTML parser (.NET).
I'm working on a browser-like application which gets HTML from a site (any website) then applies a style-script over it to change certain elements (just like greasemonkey).
My initial plan is to parse the HTML using XPath and XmlDocument, but is there a better way?
Thanks in advance!
Ps> Handy tips, tricks & links on HTML+C# would be great~ ^^
use the HTML Aglility pack. You can find it here: http://www.codeplex.com/htmlagilitypack
HTML is not always follows XML rules, for example there are tags in html, that may not have close tag, so XPath and XDocument will sometimes throw errors. IE API gives you ability to do that(see here), you can also find 3-rd party parsers for that (see this o this)
I would highly recomend using XSLT. This allows you to keep all your transformational data OUTSIDE your code, and therefore, making it really easy to change it if the HTML to be transformed is modified, or you want to change your layout.
Non the less, if using HTML and not XHTML, beware of possible errors. Non the less, using a Tidy library can help you overcome this.
I would really recommend using a package for your programming language of choice that handles all the oddities of HTML parsing. I've used Hpricot in Ruby before and it's made things a breeze.
If you want to be able to browse the HTML based on its content, XPath is a good choice. But you'll have to clean up the HTML first. You can use HTML tidy to convert the HTML to XHTML. In the process you might modify how the page renders. But it seems to be the purpose of your project so that's not a big deal.
I'm trying to load a piece of (possibly) malformed HTML into an XMLDocument object, but it fails with XMLExceptions... since there are extra opening/closing tags, and malformed XML tags such as <img > instead of <img />
How do I get the XML to parse with all the errors in the data? Is there any XML validator that I can apply before parsing, to correct these errors? Or would handling the exception parse whatever can be parsed?
The HTML Agility Pack will parse html, rather than xhtml, and is quite forgiving. The object model will be familiar if you've used XmlDocument.
You might want to check out the answer to this question.
Basically somewhere between a .NET port of beautifulsoup and the HTML agility pack there is a way.
It's unlikely that you will be able to build an XmlDocument that has this level of malformed structure. XmlDocument (to my knowledge) requires that xml content adhere to proper nesting and closure syntax.
However, you suspect that you could parse this with an XmlReader instead. It may still throw exceptions if certain egregious errors are encountered, but according to the MSDN docs, it can at least disclose the location of the errors.
If you're just dealing with HTML, there is the HTML Agility Pack, which may serve your purposes.
Depending ont he specific needs, you might be able to use HTML Tidy to cleanup the document, then import it using the XMLDocument object.
What you are trying to do is very difficult. HTML cannot be parsed using an XML parser since XML is strict and HTML is not. If that HTML were compliant XHTML (HTML as XML), then an XML parser would parse the HTML without issue.
You might want to see if there are any HTML to XHTML converters out there, if you really want to use an XML parser for HTML.
In other words, I have yet to meet an XML parser that handles malformed XML... they are not designed to accept loose markup like HTML (for good reason, too :) )
You can't load malformed XML into a XmlDocument.
Check out the Html Agility Pack on CodePlex
I have XHTML files whose source is not completely valid, it does not follow the DTD of an XML document.
Like there are places where for " it uses &Idquo; or for apostrophes it uses ’. This causes exceptions in my C# code.
So is there any method or any weblink that i can use to get rid of this?
If the file is otherwise well-formed you can define the character entities in your own DTD.
If the file is ill-formed the HTML Agility Pack from CodePlex will parse it.
You could parse the document as HTML instead since they both end up in a DOM and HTML parsers scoff at these pansy quotation mark problems. Going along with unknown's HTML Tidy idea, you could then serialize the DOM back into a valid XHTML file. (This is identical to using HTML Tidy, wihch presumably uses an HTML parser anyway, except you'd do it from C# programatically.)
Well by the nature of XML it needs to be valid otherwise it won't render at all. I'd first see what type of errors it generates with W3C's validator http://validator.w3.org/
Also consider using HTML tidy, which can be configured to fix XML as well.
We use hpricot to fix our XML, but then again we are building rails apps. Not sure about C#
What's the best way to parse fragments of HTML in C#?
For context, I've inherited an application that uses a great deal of composite controls, which is fine, but a good deal of the controls are rendered using a long sequence of literal controls, which is fairly terrifying. I'm trying to get the application into unit tests, and I want to get these controls under tests that will find out if they're generating well formed HTML, and in a dream solution, validate that HTML.
Have a look at the HTMLAgility pack. It's very compatible with the .NET XmlDocument class, but it much more forgiving about HTML that's not clean/valid XHTML.
If the HTML is XHTML compliant, you can use the built in System.Xml namespace.
I've used an SGMLReader to produce a valid Xml document from HTML and then parse what is required using XPath or to another format using XSLT. .
You can also look into HTML Tidy for HTML parsing/cleanup. I don't think they have specific .NET libraries, but you might be able to run the binary via command-line, or IKVM the java libraries.