XML SelectNodes and RemoveChild

Question

Hello , I am kind of new to C# and .NET environment and try to understand (not a solution) the following behavior by using the SelectNodes and RemoveChild.

I have some xml file that is generated and contains duplicates and I d like to remove these duplicates.
The original xml is :

134318-example.xml

I would like to output a new file that is :

134367-example-out-correct.xml

For that purpose I created a windows application form that runs under .NET Core 3.1 and the following core programm :

XmlDocument doc = new XmlDocument();  
doc.Load(rmvDupe.filePath);  
  
XmlNode root = doc.FirstChild;  
XmlNodeList nodeList = root.SelectNodes("/descendant::*"); //I wish I could use root.SelectNodes("/descendant::UniqueID") but this does not work in C#  
List<string> UniqueIDs = new List<string>() { };  
  
foreach (XmlNode node in nodeList)  
{  
    if (node.Name == "UniqueID")  
    {  
        if (!UniqueIDs.Contains(node.LastChild.Value))  
        {  
            UniqueIDs.Add(node.LastChild.Value);  
        }  
        else  
        {     
            node.ParentNode.ParentNode.RemoveChild(node.ParentNode);  
              
        }  
  
    }  
  
}  
  
doc.Save(outfilepath);  

So this code will only remove the first duplicate (134324-example-out-incorrect.xml) and for some reason when I debug under visual studio pro I see by putting a breakpoint at line 26 that nodeList gets modified in the process. What is also awkward is that if I set a breakpoint by the creation of the nodeList (line 5) that I step over once and then continue, it will generate the correct result ?

Kind Regards

Answer 1

I tested it with the file you provided, and it did produce wrong results. The error appeared on line 1042:

   <UniqueID>CA_9445df0f3a544807af6c1527ee67f90b</UniqueID>  

Using the Cast method is not enough, we also need to add the ToList method after it.

          foreach (XmlNode node in nodeList.Cast<XmlNode>().ToList())  

After adding this, the generated result is the same as the correct sample file.

          string[] lines =  File.ReadAllLines(@"C:\...\example-out-correct.xml");  
          string[] lines1 = File.ReadAllLines(@"C:\...\Desktop\myResult.xml");  
            for (int i = 0; i < lines.Count(); i++)  
            {  
                if (lines[i]!=lines1[i])  
                {  
                    Console.WriteLine(i+1);  
                    break;  
                }  
            }  
            Console.ReadKey();  

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Answer 2

you should never add / delete objects in a collection you are iterating over. You should copy the collection first:

foreach (XmlNode node in nodeList.ToList())