Question

I’m writing an application in C#. I already an .xml file that is not empty and I want to add new values to it, without deleting the existing values.

I have tried this code:

First:

FileStream docNewUser = new FileStream(@"C:\\MyApp\\MySubDir\\Data\\" + pr + ".xml", FileMode.Open);
XmlTextWriter xmlNewUser = new XmlTextWriter(docNewUser, null);
xmlNewUser.WriteStartDocument();

xmlNewUser.WriteStartElement("RootEl");//root 

xmlNewUser.WriteStartElement("Zapis");

xmlNewUser.WriteStartElement("Name");
xmlNewUser.WriteString(txtEnterName.Text);
xmlNewUser.WriteEndElement();

xmlNewUser.WriteEndElement();//end of zapis                

this.Close();

Second:

FileStream docNewUser = new FileStream(@"C:\\MyApp\\MySubDir\\Data\\" + pr + ".xml", FileMode.Open);
XmlTextWriter xmlNewUser = new XmlTextWriter(docNewUser, null);
xmlNewUser.WriteStartDocument();

xmlNewUser.WriteStartElement("RootEl");//root-ot

xmlNewUser.WriteStartElement("Zapis");

xmlNewUser.WriteStartElement("Name");
xmlNewUser.WriteString(txtEnterName.Text);
xmlNewUser.WriteEndElement();

xmlNewUser.WriteEndElement();//end of zapis                

xmlNewUser.WriteElementString("Ime", null, txtEnterName.Text);

this.Close();

Third:

FileStream docNewUser = new FileStream(@"C:\\MyApp\\MySubDir\\Data\\" + pr + ".xml", FileMode.Open);
XmlTextWriter xmlNewUser = new XmlTextWriter(docNewUser, null);
xmlNewUser.WriteStartDocument();

xmlNewUser.WriteStartElement("Zapis");

xmlNewUser.WriteStartElement("Name");
xmlNewUser.WriteString(txtEnterName.Text);
xmlNewUser.WriteEndElement();

xmlNewUser.WriteEndElement();//end of zapis                

xmlNewUser.WriteElementString("Ime", null, txtEnterName.Text);

this.Close();

I think the problem is that the stream doesn’t know where to put the new value.
some more information: the root element is already entered.

Answer 1

Use XmlDocument:

XmlDocument doc = new XmlDocument();
doc.Load("filepath");
XmlNode node = doc["MainNode"]["subnode1"]["subnode2"]; //to fetch the node after which you'd like to add something.
XmlElement stuffToAdd = doc.CreateNode("nodename");
stuffToAdd.InnerText = "the value of your added node";
node.AddChild(stuffToAdd);
doc.Save("filepath");

I’m doing this out of memory, so the names of the methods are aproximate.

As said in another answer, loading big XML files using XmlElement can be costy, because it is fully loaded in memory when you call Load().