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POExample to use a hashcode to detect if an element of a List<string> has changed C#
 

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  1. POExample to use a hashcode to detect if an element of a List<string> has changed C#
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    <p>I have a List that updates every minute based on a Linq query of some XML elements.</p> <p>the xml changes, from time to time. It was suggested to me that I could use Hashcode to determine if any of the strings in the list have changed.</p> <p>I have seen some examples of Md5 hashcode calculations for just a string, but not for a list...could someone show me a way of doing this with a list?</p> <p>I tried something simple like int test = list1.GetHashCode; but the code is the same no matter what is in the list...</p> <p>here is the entire method with the link query and all..note the SequenceEqual at the end:</p> <pre><code> private void GetTrackInfo() { _currentTitles1.Clear(); var savedxmltracks = new XDocument(); listBox1.Items.Clear(); WebClient webClient = new WebClient(); XmlDocument xmltracks = new XmlDataDocument(); try { xmltracks.Load(_NPUrl); xmltracks.Save("xmltracks.xml"); } catch (WebException ex) { StatusLabel1.Text = ex.Message; } try { savedxmltracks = XDocument.Load("xmltracks.xml"); } catch (Exception ex) { StatusLabel1.Text = ex.Message; } var dateQuery = from c in savedxmltracks.Descendants("content") select c; _count = savedxmltracks.Element("content").Element("collection").Attribute("count").Value; var tracksQuery1 = from c in savedxmltracks.Descendants("data") select new { title = c.Attribute("title").Value, imageurl = c.Attribute("image").Value, price = c.Attribute("price").Value, description = c.Attribute("productdescription").Value, qualifier = c.Attribute("pricequalifier").Value }; var xml = new XDocument(new XDeclaration("1.0", "utf-8", "yes"), new XElement("LastUsedSettings", new XElement("TimerInterval", new XElement("Interval", Convert.ToString(numericUpDown1.Value))), new XElement("NowPlayingURL", new XElement("URL", _NPUrl)), new XElement("Email", emailAddress), new XElement("LastUpdated", DateTime.Now.ToString()))); XElement StoreItems = new XElement("StoreItems"); int i = 0; foreach (var c in tracksQuery1) { if (c.title.Length &lt;= 40 &amp; c.qualifier.Length &lt;= 12 &amp; i &lt; 10) { if (c.title != null) _title1 = c.title; if (c.imageurl != null) _imageUrl = c.imageurl; if (c.price != null) _price = c.price; if (c.description != null) _productDescription = c.description; if (c.qualifier != null) _priceQualifier = c.qualifier; //} StoreItems.Add(new XElement("Title" + i.ToString(), _title1)); _currentTitles1.Add(_title1); if (_oldTitles1.Count &gt; 0) { Console.WriteLine("OldTitle: {0}, NewTitle: {1}", _oldTitles1[i], _currentTitles1[i]); } StoreItems.Add(new XElement("Price" + i.ToString(), _price)); StoreItems.Add(new XElement("Description" + i.ToString(), _productDescription)); StoreItems.Add(new XElement("PriceQualifier" + i.ToString(), _priceQualifier)); listBox1.Items.Add("Title: " + _title1); listBox1.Items.Add("Image URL: " + _imageUrl); listBox1.Items.Add("Price: " + _price); listBox1.Items.Add("Description: " + _productDescription); listBox1.Items.Add("PriceQualifier: " + _priceQualifier); try { imageData = webClient.DownloadData(_imageUrl); } catch (WebException ex) { StatusLabel1.Text = ex.Message; } MemoryStream stream = new MemoryStream(imageData); Image img = Image.FromStream(stream); //Image saveimage = img; //saveimage.Save("pic.jpg"); img.Save("pic" + i.ToString() + ".jpg"); stream.Close(); i++; } } //Console.WriteLine("Count: " + _count); Console.WriteLine("oldTitles Count: " + _oldTitles1.Count.ToString()); Console.WriteLine("currentTitles Count: " + _currentTitles1.Count.ToString()); if (_oldTitles1.Count == 0) _oldTitles1 = _currentTitles1; if (!_oldTitles1.SequenceEqual(_currentTitles1)) { Console.WriteLine("Items Changed!"); SendMail(); _oldTitles1 = _currentTitles1; } xml.Root.Add(StoreItems); xml.Save("settings.xml"); } </code></pre>
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    1. USVulcanCCIT
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    1. CODo you want to figure out if *any* element of the list has changed, or *which specific* element(s) did change?
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      1. USLasse Vågsæther Karlsen
    2. CODo you care if the elements change order?
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    3. CORecommended reading: The accepted answer to [this question](http://stackoverflow.com/questions/462451/gethashcode-guidelines-in-c) contains a link to a blog post by Eric Lippert that explains why `list1.GetHashCode()` stays the same all the time.
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      1. UStakrl
 

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