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POThe variable return null all the time
 

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  1. POThe variable return null all the time
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    <p>My program is a webcrawler. Im trying to download images from a website. In my webcrawler site i did:</p> <pre><code>try { HtmlAgilityPack.HtmlDocument doc = TimeOut.getHtmlDocumentWebClient(mainUrl, false, "", 0, "", ""); if (doc == null) { if (wccfg.downloadcontent == true) { retwebcontent.retrieveImages(mainUrl); } failed = true; wccfg.failedUrls++; failed = false; } </code></pre> <p>For example when doc is null the mainUrl contain:</p> <pre><code>http://members.tripod.com/~VanessaWest/bundybowman2.jpg </code></pre> <p>Now its jumping to the retrieveImages method in the other class:</p> <pre><code>namespace GatherLinks { class RetrieveWebContent { HtmlAgilityPack.HtmlDocument doc; string imgg; int images; public RetrieveWebContent() { images = 0; } public List&lt;string&gt; retrieveImages(string address) { try { doc = new HtmlAgilityPack.HtmlDocument(); System.Net.WebClient wc = new System.Net.WebClient(); List&lt;string&gt; imgList = new List&lt;string&gt;(); doc.Load(wc.OpenRead(address)); HtmlNodeCollection imgs = doc.DocumentNode.SelectNodes("//img[@src]"); if (imgs == null) return new List&lt;string&gt;(); foreach (HtmlNode img in imgs) { if (img.Attributes["src"] == null) continue; HtmlAttribute src = img.Attributes["src"]; imgList.Add(src.Value); if (src.Value.StartsWith("http") || src.Value.StartsWith("https") || src.Value.StartsWith("www")) { images++; string[] arr = src.Value.Split('/'); imgg = arr[arr.Length - 1]; //imgg = Path.GetFileName(new Uri(src.Value).LocalPath); //wc.DownloadFile(src.Value, @"d:\MyImages\" + imgg); wc.DownloadFile(src.Value, "d:\\MyImages\\" + Guid.NewGuid() + ".jpg"); } } return imgList; } catch { Logger.Write("There Was Problem Downloading The Image: " + imgg); return null; } } } } </code></pre> <p>Now im using a breakpoint and step line by line and after doing this line:</p> <pre><code>HtmlNodeCollection imgs = doc.DocumentNode.SelectNodes("//img[@src]"); </code></pre> <p>The variable imgs is null. Then on the next line that check if its null its jumping to the end and does nothing.</p> <p>How can i solve it so it will be able to download the image from <a href="http://members.tripod.com/~VanessaWest/bundybowman2.jpg" rel="nofollow">http://members.tripod.com/~VanessaWest/bundybowman2.jpg</a> ?</p> <p>EDIT**</p> <pre><code>public List&lt;string&gt; retrieveImages(string address) { try { doc = new HtmlAgilityPack.HtmlDocument(); System.Net.WebClient wc = new System.Net.WebClient(); List&lt;string&gt; imgList = new List&lt;string&gt;(); doc.Load(wc.OpenRead(address)); string t = doc.DocumentNode.InnerText; HtmlNodeCollection imgs = doc.DocumentNode.SelectNodes("//img//[@src]"); if (imgs == null) return new List&lt;string&gt;(); foreach (HtmlNode img in imgs) { if (img.Attributes["src"] == null) continue; HtmlAttribute src = img.Attributes["src"]; wc.DownloadFile(src.Value, "d:\\MyImages\\" + Guid.NewGuid() + ".jpg"); imgList.Add(src.Value); if (src.Value.StartsWith("http") || src.Value.StartsWith("https") || src.Value.StartsWith("www")) { images++; string[] arr = src.Value.Split('/'); imgg = arr[arr.Length - 1]; //imgg = Path.GetFileName(new Uri(src.Value).LocalPath); //wc.DownloadFile(src.Value, @"d:\MyImages\" + imgg); wc.DownloadFile(src.Value, "d:\\MyImages\\" + Guid.NewGuid() + ".jpg"); } } return imgList; } catch { Logger.Write("There Was Problem Downloading The Image: " + imgg); return null; } } </code></pre>
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    1. USDanielVest
    1. USDanielVest
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    1. COhave you try with mainUrl as `http://vanessawest.tripod.com/bundybowman2.jpg`?
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      1. POThe variable return null all the time
      1. USDamith
    2. COIf you checked `doc` is correct (line before `imgs = doc....`) then you probably has wrong selector (`"//img[@src]"`). Google how to repair selector. If selector is correct, you have problem somewhere else and you should debug to find first line with wrong behaviour
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      1. POThe variable return null all the time
      1. USAri
    3. COJust a tip. By the collections code conventions defined by MS, you should return an empty list instead of null. There is also a question regarding this problem on SO: http://stackoverflow.com/q/1969993/809009.
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      1. POThe variable return null all the time
      1. USOndrej Janacek
 

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