Scraping Multiple Pages in CSharp with HtmlAgilityPack

Oct 15, 2023 · 4 min read

Web scraping is useful to programmatically extract data from websites. Often you need to scrape multiple pages from a site to gather complete information. In this article, we'll see how to scrape multiple pages in C# using the HtmlAgilityPack library.

Prerequisites

To follow along, you'll need:

  • Basic C# knowledge
  • .NET Core installed
  • HtmlAgilityPack NuGet package
  • dotnet add package HtmlAgilityPack
    

    Import Libraries

    We'll need the following namespaces:

    using System.Net.Http;
    using HtmlAgilityPack;
    

    Define Base URL

    We'll scrape a blog - https://copyblogger.com/blog/. The page URLs follow a pattern:

    <https://copyblogger.com/blog/>
    <https://copyblogger.com/blog/page/2/>
    <https://copyblogger.com/blog/page/3/>
    

    Let's define the base URL pattern:

    string baseUrl = "<https://copyblogger.com/blog/page/{0}/>";
    

    The {0} allows us to insert the page number.

    Specify Number of Pages

    Next, we'll specify how many pages to scrape. Let's scrape the first 5 pages:

    int numPages = 5;
    

    Loop Through Pages

    We can now loop from 1 to numPages and construct the URL for each page:

    for (int pageNum = 1; pageNum <= numPages; pageNum++)
    {
    
      // Construct page URL
      string url = string.Format(baseUrl, pageNum);
    
      // Code to scrape each page
    
    }
    

    Send Request and Check Response

    Inside the loop, we'll use HttpClient to send a request to the page URL:

    HttpClient client = new HttpClient();
    HttpResponseMessage response = await client.GetAsync(url);
    
    if (response.IsSuccessStatusCode)
    {
      // Scrape page
    }
    else
    {
      Console.WriteLine("Failed to retrieve page " + pageNum);
    }
    

    We check for a success status code to ensure the request succeeded.

    Parse HTML

    If successful, we can parse the HTML using HtmlAgilityPack:

    HtmlDocument htmlDoc = new HtmlDocument();
    htmlDoc.LoadHtml(await response.Content.ReadAsStringAsync());
    

    This gives us a DOM document to extract data from.

    Extract Data

    Now within the loop we can use htmlDoc to find and extract data from each page.

    For example, to get all article elements:

    var articles = htmlDoc.DocumentNode.SelectNodes("//article");
    

    We can loop through articles and extract information like title, URL, author etc.

    Full Code

    Our full code to scrape 5 pages is:

    using System.Net.Http;
    using HtmlAgilityPack;
    
    string baseUrl = "<https://copyblogger.com/blog/page/{0}/>";
    int numPages = 5;
    
    for (int pageNum = 1; pageNum <= numPages; pageNum++)
    {
    
      string url = string.Format(baseUrl, pageNum);
    
      HttpClient client = new HttpClient();
      HttpResponseMessage response = await client.GetAsync(url);
    
      if (response.IsSuccessStatusCode)
      {
    
        HtmlDocument htmlDoc = new HtmlDocument();
        htmlDoc.LoadHtml(await response.Content.ReadAsStringAsync());
    
        var articles = htmlDoc.DocumentNode.SelectNodes("//article");
    
        foreach (var article in articles)
        {
    
          // Extract data from article
    
          string title = article.SelectSingleNode("./h2[@class='entry-title']").InnerText.Trim();
          string url = article.SelectSingleNode("./a[@class='entry-title-link']").GetAttributeValue("href", null);
          string author = article.SelectSingleNode("./div[@class='post-author']/a").InnerText.Trim();
    
          List<string> categories = new List<string>();
          foreach (var node in article.SelectNodes("./div[@class='entry-categories']/a"))
          {
            categories.Add(node.InnerText.Trim());
          }
    
          // Print extracted data
          Console.WriteLine("Title: " + title);
          Console.WriteLine("URL: " + url);
          Console.WriteLine("Author: " + author);
          Console.WriteLine("Categories: " + string.Join(", ", categories));
          Console.WriteLine();
    
        }
    
      }
      else
      {
        Console.WriteLine("Failed to retrieve page " + pageNum);
      }
    
    }
    

    This allows us to scrape and extract data from multiple pages sequentially. The full code can be extended to scrape any number of pages.

    Summary

  • Use a base URL pattern with {0} placeholder
  • Loop through pages with for loop
  • Construct each page URL
  • Send request with HttpClient and check response
  • Parse HTML using HtmlAgilityPack
  • Find and extract data inside loop
  • Print or store scraped data
  • Web scraping enables collecting large datasets programmatically. With the techniques here, you can scrape and extract information from multiple pages of a website in C#.

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