


How to Retrieve Dynamically Generated HTML Code from Web Browser Controls?
Oct 18, 2024 am 08:35 AMHow to Dynamically Generate HTML Code Using .NET's WebBrowser or mshtml.HTMLDocument?
Problem:
Retrieving dynamically generated HTML code from a web page using the WebBrowser class or mshtml.HTMLDocument interface can be a challenge. The WebBrowser class fails to capture the rendered HTML, and mshtml.HTMLDocument returns raw HTML that differs from the actual page content.
Solution:
Using WebBrowser Class:
Although the WebBrowser class does not provide a direct method for obtaining the rendered HTML, it is possible to implement a workaround. Add a WebBrowser control to a form, have it navigate to the desired URL, and then use the following steps to retrieve the HTML:
- Send "CTRL A" keys to select all content.
- Use the Copy method to copy the selection to the clipboard.
- Paste the HTML from the clipboard and parse it as needed.
Using mshtml.HTMLDocument Interface:
- Create an instance of mshtml.HTMLDocument and pass it the downloaded HTML using write.
- Check for changes in the HTML snapshot by polling the all property and the IsBusy property of the WebBrowser control.
- Once the IsBusy property becomes false and there are no changes in the HTML snapshot, consider the page to be fully rendered and retrieve the HTML.
Additional Considerations:
- Ensure HTML5 rendering is enabled using Browser Feature Control.
- Use a timeout to prevent infinite rendering.
- Async/await can simplify the implementation of the polling logic.
Example Code:
<code class="C#">using Microsoft.Win32; using System; using System.Threading; using System.Threading.Tasks; using mshtml; public async Task<string> LoadDynamicPage(string url, CancellationToken token) { var doc = new HTMLDocument(); doc.write(new System.Net.WebClient().DownloadString(url)); // Poll for changes in HTML snapshot var html = doc.documentElement.outerHTML; while (true) { await Task.Delay(500, token); var htmlNow = doc.documentElement.outerHTML; if (html == htmlNow) break; html = htmlNow; } return html; }</code>
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