To write XML, create an XmlTextWriter that wraps a stream and use Write methods (such as WriteStartElement and WriteEndElement). To read XML, create an XmlTextReader that wraps a stream and call Read to move from node to node.

To write XML to any stream, you can use the streamlined XmlTextWriter. It provides Write methods that write one node at a time. These include

• WriteStartDocument, which writes the document prologue, and WriteEndDocument, which closes any open elements at the end of the document.

• WriteStartElement, which writes an opening tag for the element you specify. You can then add more elements nested inside this element, or you can call WriteEndElement to write the closing tag.

• WriteElementString, which writes an entire element, with an opening tag, a closing tag, and text content.

• WriteAttributeString, which writes an entire attribute for the nearest open element, with a name and value.

To read the XML, you use the Read method of the XmlTextReader. This method advances the reader to the next node, and returns true. If no more nodes can be found, it returns false. You can retrieve information about the current node through XmlTextReader properties, including its Name, Value, and NodeType.


EX：

using System;
using System.Xml;
using System.IO;
using System.Text;

public class ReadWriteXml {

    private static void Main() {

        // Create the file and writer.
        FileStream fs = new FileStream("products.xml", FileMode.Create);
        XmlTextWriter w = new XmlTextWriter(fs, Encoding.UTF8);

        // Start the document.
        w.WriteStartDocument();
        w.WriteStartElement("products");

        // Write a product.
        w.WriteStartElement("product");
        w.WriteAttributeString("id", "1001");
        w.WriteElementString("productName", "Gourmet Coffee");
        w.WriteElementString("productPrice", "0.99");
        w.WriteEndElement();

        // Write another product.
        w.WriteStartElement("product");
        w.WriteAttributeString("id", "1002");
        w.WriteElementString("productName", "Blue China Tea Pot");
        w.WriteElementString("productPrice", "102.99");
        w.WriteEndElement();

        // End the document.
        w.WriteEndElement();
        w.WriteEndDocument();
        w.Flush();
        fs.Close();

        Console.WriteLine("Document created. " +
         "Press Enter to read the document.");
        Console.ReadLine();

        fs = new FileStream("products.xml", FileMode.Open);
        XmlTextReader r = new XmlTextReader(fs);

        // Read all nodes.
        while (r.Read()) {
 
           if (r.NodeType == XmlNodeType.Element) {

                Console.WriteLine();
                Console.WriteLine("<" + r.Name + ">");

                if (r.HasAttributes) {

                    for (int i = 0; i < r.AttributeCount; i++) {
                        Console.WriteLine("\tATTRIBUTE: " +
                          r.GetAttribute(i));
                    }
                }
            }else if (r.NodeType == XmlNodeType.Text) {
                Console.WriteLine("\tVALUE: " + r.Value);
            }
        }
        Console.ReadLine();
    }
}

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 Insert Nodes in an XML Document





Solution
Create the node using the appropriate XmlDocument method (such as CreateElement, CreateAttribute,
 CreateNode, and so on). Then insert it using the appropriate XmlNode method (such as InsertAfter,
 InsertBefore, or AppendChild).

The following example demonstrates this technique by programmatically creating a new XML document. 
using System;
using System.Xml;

public class GenerateXml {

    private static void Main() {

        // Create a new, empty document.
        XmlDocument doc = new XmlDocument();
        XmlNode docNode = doc.CreateXmlDeclaration("1.0", "UTF-8", null);
        doc.AppendChild(docNode);

        // Create and insert a new element.
        XmlNode productsNode = doc.CreateElement("products");
        doc.AppendChild(productsNode);

        // Create a nested element (with an attribute).
        XmlNode productNode = doc.CreateElement("product");
        XmlAttribute productAttribute = doc.CreateAttribute("id");
        productAttribute.Value = "1001";
        productNode.Attributes.Append(productAttribute);
        productsNode.AppendChild(productNode);

        // Create and add the sub-elements for this product node
        // (with contained text data).
        XmlNode nameNode = doc.CreateElement("productName");
        nameNode.AppendChild(doc.CreateTextNode("Gourmet Coffee"));
        productNode.AppendChild(nameNode);
        XmlNode priceNode = doc.CreateElement("productPrice");
        priceNode.AppendChild(doc.CreateTextNode("0.99"));
        productNode.AppendChild(priceNode);

        // Create and add another product node.
        productNode = doc.CreateElement("product");
        productAttribute = doc.CreateAttribute("id");
        productAttribute.Value = "1002";
        productNode.Attributes.Append(productAttribute);
        productsNode.AppendChild(productNode);
        nameNode = doc.CreateElement("productName");
        nameNode.AppendChild(doc.CreateTextNode("Blue China Tea Pot"));
        productNode.AppendChild(nameNode);
        priceNode = doc.CreateElement("productPrice");
        priceNode.AppendChild(doc.CreateTextNode("102.99"));
        productNode.AppendChild(priceNode);

        // Save the document (to the Console window rather than a file).
        doc.Save(Console.Out);
        Console.ReadLine();
    }
}
The generated document looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<products>
  <product id="1001">
    <productName>Gourmet Coffee</productName>
    <productPrice>0.99</productPrice>
  </product>
  <product id="1002">
    <productName>Blue China Tea Pot</productName>
    <productPrice>102.99</productPrice>
  </product>
</products>
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Quickly Append Nodes in an XML Document
Solution
Create a helper function that accepts a tag name and content and can generate the entire element
 at once. Alternatively, use the XmlDocument.CloneNode method to copy branches of an XmlDocument.

Here's an example of one such helper class:
using System;
using System.Xml;

public class XmlHelper {

    public static XmlNode AddElement(string tagName, 
      string textContent, XmlNode parent) {

        XmlNode node = parent.OwnerDocument.CreateElement(tagName);
        parent.AppendChild(node);

        if (textContent != null) {

            XmlNode content;
            content = parent.OwnerDocument.CreateTextNode(textContent);
            node.AppendChild(content);
        }
        return node;
    }

    public static XmlNode AddAttribute(string attributeName,
      string textContent, XmlNode parent) {

        XmlAttribute attribute;
        attribute = parent.OwnerDocument.CreateAttribute(attributeName);
        attribute.Value = textContent;
        parent.Attributes.Append(attribute);

        return attribute;
    }
}
You can now condense the XML-generating code from recipe 5.2 with the simpler syntax shown here:
public class GenerateXml {

    private static void Main() {

        // Create the basic document.
        XmlDocument doc = new XmlDocument();
        XmlNode docNode = doc.CreateXmlDeclaration("1.0", "UTF-8", null);
        doc.AppendChild(docNode);
        XmlNode products = doc.CreateElement("products");
        doc.AppendChild(products);

        // Add two products.
        XmlNode product = XmlHelper.AddElement("product", null, products);
        XmlHelper.AddAttribute("id", "1001", product);
        XmlHelper.AddElement("productName", "Gourmet Coffee", product);
        XmlHelper.AddElement("productPrice", "0.99", product);

        product = XmlHelper.AddElement("product", null, products);
        XmlHelper.AddAttribute("id", "1002", product);
        XmlHelper.AddElement("productName", "Blue China Tea Pot", product);
        XmlHelper.AddElement("productPrice", "102.99", product);

        // Save the document (to the Console window rather than a file).
        doc.Save(Console.Out);
        Console.ReadLine();
    }
}
Alternatively, you might want to take the helper methods such as AddAttribute and AddElement and
 make them instance methods in a custom class you derive from XmlDocument.
Another approach to simplifying writing XML is to duplicate nodes using the XmlNode.CloneNode 
method. CloneNode accepts a Boolean deep parameter. If you supply true, CloneNode will duplicate
 the entire branch, with all nested nodes.
Here's an example that creates a new product node by copying the first node. 
// (Add first product node.)

// Create a new element based on an existing product.
product = product.CloneNode(true);

// Modify the node data.
product.Attributes[0].Value = "1002";
product.ChildNodes[0].ChildNodes[0].Value = "Blue China Tea Pot";
product.ChildNodes[1].ChildNodes[0].Value = "102.99";

// Add the new element.
products.AppendChild(product);
Notice that in this case, certain assumptions are being made about the existing nodes (for example,
 that the first child in the item node is always the name, and the second child is always the 
price). If this assumption isn't guaranteed to be true, you might need to examine the node name
 programmatically.