XML in .NET: .NET Framework XML Classes and C# Offer Simple, Scalable Data Manipulation

XML = .NET Technology Substrate

Abstract Base Classes

  public void ReadDocument(XmlReader reader)
{
  // read (pull) the next node in document order
  while (reader.Read())
  {
    // get the current node's (namespace) name
    String sNodeName = (reader.NodeType == XmlNodeType.Element ||
      reader.NodeType == XmlNodeType.EndElement) ?
      reader.NamespaceURI + "#" + reader.Name : reader.Name;
    Console.WriteLine(sNodeName);      
  }
}

  public void WriteDocument(XmlWriter writer)
{
  writer.WriteStartDocument();
  writer.WriteComment("generated by SampleWriter");
  writer.WriteProcessingInstruction("hack", "on person");
  writer.WriteStartElement("p", "person", "urn:person");
  writer.WriteStartElement("name", "");
  writer.WriteString("joebob");
  writer.WriteEndElement();
  writer.WriteElementInt16("age", "", 28);
  writer.WriteEndElement();
  writer.WriteEndDocument();
}

  <?xml version="1.0"?>
<!--sample person document--> 
<?hack on person?>
<p:person xmlns:p="urn:person">
  <name>joebob</name>
  <age unit="year">28</age>
</p:person>

XmlReader

Inspecting the Current Node

  public static void InspectCurrentNode(XmlReader reader)
{
  String sQName = reader.Name;
  String sLocalName = reader.LocalName;
  String sNSURI = reader.NamespaceURI;
  XmlNodeType type = reader.NodeType;
  String sValue = reader.Value;
  boolean bAtts = reader.HasAttributes;
  int nAtts = reader.AttributeCount;
  •••
  // do something with data
}

Reading Nodes

  public void TraverseInDocumentOrder(XmlReader reader)
{
  try {
    while (reader.Read())
        Console.WriteLine("{0}", reader.NodeType);
}
catch(XmlException e) {
    Console.WriteLine("###error: " + e.Message);
 }
} 

  <?xml version="1.0"?>
<!--sample person document--> 
<?hack on person?>
<p:person xmlns:p="urn:person">
  <name>joebob</name>
  <age unit="year">28</age>
</p:person>

  try
{
  // if the current node doesn't have a local name
  // of "foo" and a namespace URI of "urn:bar", an
  // exception is thrown
  reader.ReadStartElement("foo", "urn:bar");
}
catch(XmlException e)
{
  Console.WriteLine(e.Message);
}  

  // sum all Price elements
double dTotal = 0.0;
while (reader.Read())
{
  if (reader.NodeType == XmlNodeType.Element)
  {
    if (reader.LocalName.Equals("Price"))
      dTotal += reader.ReadDouble();
  }
}
Console.WriteLine(dTotal);  

  public static void ReadAttributes(XmlReader reader)
{
  while (reader.Read())
  {
    if (reader.NodeType == XmlNodeType.Element)
      // process all of the element's attributes
      for (int i=0; i<reader.AttributeCount; i++)
        Console.WriteLine(reader.GetAttribute(i));
  }
} 

Expanding Entity References

  while (reader.Read())
{
  if (reader.NodeType == XmlNodeType.Element)
    Console.WriteLine(reader.Name);
  if (reader.NodeType == XmlNodeType.EntityReference)
  {
    Console.WriteLine("*** resolve entity called ***");
    // after this call, the reader iterates over the
    // entity's content
    reader.ResolveEntity();
  }
  if (reader.NodeType == XmlNodeType.EndEntity)
    Console.WriteLine("*** end of current entity ***");
}      

  <!DOCTYPE person [
  <!ENTITY fl "<first>Bob</first><last>Smith</last>">
]>
<person>
  <name>&fl;</name>
  <age>35</age>
</person>

  person
name
_** resolve entity called **_
first
last
_** end of entity **_
age

Attribute Fidelity

  public static void MoveToFirstContentNode(XmlReader reader)
{
  if (reader.Read())
  {
    Console.WriteLine(reader.Name);
    // skips all non-content nodes (pis, comments, whitespace)
    reader.MoveToContent(); 
    Console.WriteLine(reader.Name);
  }
}  

  <?skip me?>
<!--skip me too-->
<?and me too...?>
<foo>
  <bar/>
</foo>

  skip
foo  

XmlTextReader

  public class MyCustomResolver : XmlUrlResolver
{
  public override object GetEntity(string baseUri,
    string relativeUri, string role,
    Type t, out string resolvedUri)
  {
    resolvedUri = DoMyCustomResolution(baseUri, relativeUri);
    return GetResource(resolvedUri);
  }
}  

Other Readers

  <!-- person-xinc.xml -->
<person xmlns:xinc="https://www.w3.org/1999/XML/xinclude">
  <fullname-ref xinc:href="fullname.xml"/>
</person>
<!-- fullname.xml -->
<name>
  <first>Joe</first>
  <last>Bob</last>
</name>

  <person>
  <name>
    <first>Joe</first>
    <last>Bob</last>
  </name>
</person>

XmlWriter

  public static void Serialize(XmlReader r, XmlWriter w)
{
  while (r.Read())
    w.WriteNode(r, true);
}  

XmlTextWriter

  public static void Main(String[] args)
{
  XmlTextWriter w = new XmlTextWriter(Console.Out);
  // write namespace names
  w.Namespaces = true;
  w.EncodeNames = true;
  // indent (pretty-print) output
  w.Formatting = Formatting.Indented;
  w.Indentation = 4;
  // use ' for attribute values
  w.QuoteChar = "'";
  WriteDocument(w);
}  

DOM Implementation

  XmlDocument doc = new XmlDocument();
doc.Load("https://staff.develop.com/aarons/xmlstuff.xml");      

Navigation and XmlNavigator

  public static void EvaluateXPath(XmlNavigator nav)
{
  // returns a node-set
  nav.Select("//Price/text()");
  while (nav.MoveToNextSelected())
  {
    // process selected nodes here
  }
}  

  Object cachedExpr = null;
cachedExpr = nav.Compile("//Invoice[@id>1000]//Price[.>10]");
// can reuse expression w/out compilation cost
nav.Select(cachedExpr);
while (nav.MoveToNextSelected())
{
  // process selected nodes here
}  

  public static void EvaluateXPath(XmlNavigator in, XmlNavigator out)
{
  // returns a node-set
  in.Select("//Price");
  out.CopySelected(TreePosition.FirstChild, in);
  // out navigator now contains selected nodes
}  

  public static void SumPriceNodes(XmlNavigator nav) {
  // in this case, evaluate returns a number
  Console.WriteLine("sum=" + nav.Evaluate("sum(//Price)"));
}  

DocumentNavigator

  XmlDocument doc = new XmlDocument();
doc.Load("person.xml");
DocumentNavigator nav = new DocumentNavigator(doc);
nav.Select("/person/name");
while (nav.MoveToNextSelected())
{
  // process selection here...
}

Transformations and XslTransform

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