c#4.0 Other XML Technologies(一些XML的知识点)

URI:http://www.albahari.com/nutshell/cs4ch11.aspx

Enumerating nodes with XmlReader
使用XmlReader阅读器来对节点进行枚举读取

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<customer id="123" status="archived">
<firstname>Jim</firstname>
<lastname>Bo</lastname>
</customer>

XmlReaderSettings settings = new XmlReaderSettings();
settings.IgnoreWhitespace = true;

using (XmlReader reader = XmlReader.Create ("customer.xml", settings))
while (reader.Read())
{
Console.Write (new string (' ',reader.Depth*2));  // Write indentation
Console.WriteLine (reader.NodeType);
}

Processing XNodeType
处理多种类型的节点

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE customer [ <!ENTITY tc "Top Customer"> ]>
<customer id="123" status="archived">
<firstname>Jim</firstname>
<lastname>Bo</lastname>
<quote><![CDATA[C#'s operators include: < > &]]></quote>
<notes>Jim Bo is a &tc;</notes>
<!--  That wasn't so bad! -->
</customer>

XmlReaderSettings settings = new XmlReaderSettings();
settings.IgnoreWhitespace = true;
settings.ProhibitDtd = false;      // Must set this to read DTDs 必须要将该XML阅读器对象设置为允许读取DTD的数据

using (XmlReader r = XmlReader.Create ("customer.xml", settings))
while (r.Read())
{
Console.Write (r.NodeType.ToString().PadRight (17, '-'));
Console.Write ("> ".PadRight (r.Depth * 3));

switch (r.NodeType)
{
case XmlNodeType.Element:
case XmlNodeType.EndElement:
Console.WriteLine (r.Name); break;

case XmlNodeType.Text:
case XmlNodeType.CDATA:
case XmlNodeType.Comment:
case XmlNodeType.XmlDeclaration:
Console.WriteLine (r.Value); break;

case XmlNodeType.DocumentType:
Console.WriteLine (r.Name + " - " + r.Value); break;

default: break;
}
}

Using ReadElementContentAs
读取节点元素内容用例如：

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<customer id="123" status="archived">
<firstname>Jim</firstname>
<lastname>Bo</lastname>
<creditlimit>500.00</creditlimit>    <!-- OK, we sneaked this in! -->
</customer>

XmlReaderSettings settings = new XmlReaderSettings();
settings.IgnoreWhitespace = true;

using (XmlReader r = XmlReader.Create ("customer.xml", settings))
{
r.MoveToContent();                // Skip over the XML declaration 这里跳过XML的定义
r.ReadStartElement ("customer");
string firstName    = r.ReadElementContentAsString ("firstname", "");
string lastName     = r.ReadElementContentAsString ("lastname", "");
decimal creditLimit = r.ReadElementContentAsDecimal ("creditlimit", "");

r.MoveToContent();      // Skip over that pesky comment 这里跳过一些不相关本次操作的描述
r.ReadEndElement();     // Read the closing customer tag  将XML阅读器的指针推到当前XML文档的最后关闭标签：</customer>
}

Optional elements:
选择节点元素

r.ReadStartElement ("customer");
string firstName    = r. ReadElementContentAsString ("firstname", "");
string lastName     = r.Name == "lastname"
? r.ReadElementContentAsString() : null;
decimal creditLimit = r.ReadElementContentAsDecimal ("creditlimit", "");

Checking for an empty element:
检查空的节点元素：

bool isEmpty = reader.IsEmptyElement;
reader.ReadStartElement ("customerList");
if (!isEmpty) reader.ReadEndElement();

Reading attributes:
读取XML文档指定节点元素的特性

<customer id="123" status="archived"/>

Console.WriteLine (reader ["id"]);              // 123
Console.WriteLine (reader ["status"]);          // archived
Console.WriteLine (reader ["bogus"] == null);   // True

Console.WriteLine (reader [0]);            // 123
Console.WriteLine (reader [1]);            // archived

reader.MoveToAttribute ("status");
string status = ReadContentAsString();

reader.MoveToAttribute ("id");
int id = ReadContentAsInt();

if (reader.MoveToFirstAttribute())
do
{
Console.WriteLine (reader.Name + "=" + reader.Value);
}
while (reader.MoveToNextAttribute());

// OUTPUT:
id=123
status=archived

XmlWriter:
使用XmlWriter的XML写入器：

XmlWriterSettings settings = new XmlWriterSettings();
settings.Indent = true;

using (XmlWriter writer = XmlWriter.Create ("..\\..\\foo.xml", settings))
{
writer.WriteStartElement ("customer");
writer.WriteElementString ("firstname", "Jim");
writer.WriteElementString ("lastname"," Bo");
writer.WriteEndElement();
}

Writing attributes:
向写入指定节点元素的特性：

writer.WriteStartElement ("customer");
writer.WriteAttributeString ("id", "1");
writer.WriteAttributeString ("status", "archived");

Namespaces and prefixes：
使用XML写入器向XML文档写入节点的命名空间与前缀：

writer.WriteStartElement ("o", "customer", "http://oreilly.com");
writer.WriteElementString ("o", "firstname", "http://oreilly.com", "Jim");
writer.WriteElementString ("o", "firstname", "http://oreilly.com", "Bo");
writer.WriteEndElement();

Working with hierarchical data：
分开处理XML数据的例子：

public class Customer
{
public const string XmlName = "customer";
public int? ID;
public string FirstName, LastName;

public Customer() { }
public Customer (XmlReader r) { ReadXml (r); }

public void ReadXml (XmlReader r)
{
if (r.MoveToAttribute ("id")) ID = r.ReadContentAsInt();
r.ReadStartElement();
FirstName = r.ReadElementContentAsString ("firstname", "");
LastName = r.ReadElementContentAsString ("lastname", "");
r.ReadEndElement();
}

public void WriteXml (XmlWriter w)
{
if (ID.HasValue) w.WriteAttributeString ("id", "", ID.ToString());
w.WriteElementString ("firstname", FirstName);
w.WriteElementString ("lastname", LastName);
}
}

public class Supplier
{
public const string XmlName = "supplier";
public string Name;

public Supplier() { }
public Supplier (XmlReader r) { ReadXml (r); }

public void ReadXml (XmlReader r)
{
r.ReadStartElement();
Name = r.ReadElementContentAsString ("name", "");
r.ReadEndElement();
}

public void WriteXml (XmlWriter w)
{
w.WriteElementString ("name", Name);
}
}

public class Contacts
{
public IList<Customer> Customers = new List<Customer>();
public IList<Supplier> Suppliers = new List<Supplier>();

public void ReadXml (XmlReader r)
{
bool isEmpty = r.IsEmptyElement;           // This ensures we don't get 确保我们不操作空节点元素的文档
r.ReadStartElement();                      // snookered by an empty 该方法内部会阻止读取空的节点元素
if (isEmpty) return;                       // <contacts/> element!
while (r.NodeType == XmlNodeType.Element)
{
if (r.Name == Customer.XmlName)      Customers.Add (new Customer (r));
else if (r.Name == Supplier.XmlName) Suppliers.Add (new Supplier (r));
else
throw new XmlException ("Unexpected node: " + r.Name);
}
r.ReadEndElement();
}

public void WriteXml (XmlWriter w)
{
foreach (Customer c in Customers)
{
w.WriteStartElement (Customer.XmlName);
c.WriteXml (w);
w.WriteEndElement();
}
foreach (Supplier s in Suppliers)
{
w.WriteStartElement (Supplier.XmlName);
s.WriteXml (w);
w.WriteEndElement();
}
}
}

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