.Net Compact Framework開發（3）——XML SAX操作

XmlTextReader是隻讀的單向XML解析器，在解析發生錯誤時觸發XmlException，不支援DTD；XmlTextReader可以采用多種方法裝入XML文檔，XmlResolver屬性用于解析遠端資源；

//不支援相對路徑，必須使用完整路徑或者檔案位于root目錄

XmlTextReader reader = new XmlTextReader("filename.xml");

XmlTextReader xmlReader = new XmlTextReader("http://foo.com/bar.xml");

//如果你的網站需要密碼認證，可以采用如下方法

static void Main()

{

NetworkCredential cred =

new NetworkCredential("usrnm", "psswd", "domain");

Stream s =

GetDocumentStream("http://www/foo.com/bar.xml", cred,);

XmlTextReader reader = new XmlTextReader(s);

// Do something interesting with the XmlTextReader

}

static Stream GetDocumentStream(string address, ICredentials cred)

{

XmlUrlResolver xur = new XmlUrlResolver();

Uri uri = new Uri(address);

if(cred != null)

xur.Credentials = cred;

try

{

return (Stream)xur.GetEntity(uri, null,null);

}

catch(Exception e)

{

MessageBox.Show(e.ToString());

throw e;

}

XmlTextReader的Namespaces屬性為true的時候支援namespace，如果為false，prefix和local name被組合成local name，這個屬性必須在進行任何讀操作之前（XmlTextReader的ReadState屬性為ReadState.Initial）設定完成；

reader.Namespaces = true;

reader.MoveToContent();

MessageBox.Show("Local Name: " + reader.LocalName);

MessageBox.Show("Prefix: " + reader.Prefix);

MessageBox.Show("Namespace: " + reader.NamespaceURI);

reader.Close();

XmlTextReader的Normalization屬性控制是否對空格和attribute進行标準化，将相鄰的空格合并為一個，将entity reference替換成resolved value（不支援DTD），因為後者總是要進行的（例如對&#gt的解析），實質上Compact Framework隻進行空格合并；這個屬性可以在解析的任意時候進行；

public static void TestNormalization(bool normOn)

{

string data =

@"<Root>

New Line'/>

</Root>";

StringReader str = new StringReader(data);

XmlTextReader reader = new XmlTextReader(str);

reader.WhitespaceHandling=WhitespaceHandling.None;

reader.MoveToContent();

reader.ReadStartElement("Root");

reader.Normalization=normOn;

MessageBox.Show("Normalization On: " + normOn.ToString());

MessageBox.Show("attr's Value: " + reader.GetAttribute("attr"));

reader.Close();

}

public static void Main(string[] args)

{

// Test with normalization off

TestNormalization(false);

// Test with normalization on

TestNormalization(true);

}

XmlTextReader的WhitespaceHandling屬性決定了如何處理空格，

All ------ Both Whitespace and SignificantWhitespace nodes are returned.

None ------ No Whitespace or SignificantWhitespace nodes are returned.

Significant ------ Only SignificantWhitespace is returned.

在解析XML流的時候，XmlTextReader指向目前遇到的Node，每個Node具有4種資訊（但不是每種Node這4種資訊都有效）：Node Name, Node Namespace, Node Value, and Node Attributes；

NODE TYPE VALUE

Attribute ------ The string value of the attribute

CDATA ------ The content of the CDATA section

Comment ------ The comment of the comment node

ProcessingInstruction ------ The entire content, not including the target

SignificantWhitespace ------ The white space within an xml:space = 'preserve' scope

Text ------ The content of the text node

Whitespace ------ The white space between markup

XmlDeclaration ------ The content of the declaration

NODE TYPE Available Attribute

Element ------ Any custom attribute

XmlDeclaration ------ Version, encoding, & standalone

XmlTextReader可以通過NodeType屬性判斷目前Node的類型，通過HasValue屬性判斷目前Node是否有Value，HasAttributes屬性判斷目前Node是否有Attribute；通過Read方法來周遊讀取XML内容；

while(reader.Read())

{

switch(reader.NodeType)

{

case XmlNodeType.Element:

if(reader.IsEmptyElement)

MessageBox.Show("<" + reader.Name + "/>");

else

MessageBox.Show("<" + reader.Name + ">");

break;

case XmlNodeType.EndElement:

MessageBox.Show("</" + reader.Name + ">");

break;

case XmlNodeType.CDATA:

MessageBox.Show("<![CDATA[" + reader.Value + "]]>");

break;

case XmlNodeType.Comment:

MessageBox.Show("");

break;

case XmlNodeType.Document:

MessageBox.Show("Reading an XML document");

break;

case XmlNodeType.DocumentFragment:

MessageBox.Show("Reading an XML document fragment");

break;

case XmlNodeType.ProcessingInstruction:

MessageBox.Show("<? " +

reader.Name + " " +

reader.Value + "?>");

break;

case XmlNodeType.Text:

MessageBox.Show("Text: " + reader.Value);

break;

case XmlNodeType.XmlDeclaration:

MessageBox.Show("<?xml " + reader.Value + "?>");

break;

}

XmlTextReader的ReadStartElement方法相當于在IsStartElement方法之後調用Read方法，檢查目前Node是否是StartElement并前進到下一個節點；這個方法可以同一個Name/Namespace參數來檢查目前Node是否比對；這個方法主要用于跳過StartElement直接跳轉到Element的内容；如果你調用了ReadStartElement并且使用了這個Element中的内容，要對稱調用ReadEndElement（除非這個Element的IsEmptyElement屬性等于True）；

using (XmlReader reader = XmlReader.Create("book3.xml")) {

// Parse the XML document. ReadString is used to

// read the text content of the elements.

reader.Read();

reader.ReadStartElement("book");

reader.ReadStartElement("title");

Console.Write("The content of the title element: ");

Console.WriteLine(reader.ReadString());

reader.ReadEndElement();

reader.ReadStartElement("price");

Console.Write("The content of the price element: ");

Console.WriteLine(reader.ReadString());

reader.ReadEndElement();

}

//book3.xml

<book>

<title>Pride And Prejudice</title>

</book>

 XmlTextReader的ReadElementString方法可以讀取text-only的Element内容，其内部首先調用MoveToContent，然後讀取content傳回一個String，同時相當于調用了ReadEndElement；

reader.Read();

reader.ReadStartElement("Exercise");

string name = reader.ReadElementString();

string bodypart = reader.ReadElementString();

reader.Close();

XmlTextReader的MoveToContent方法用于快速前進到一個content node（A content node is an element, an end element, an entity reference, an end entity, or non–white space text.），在向前搜尋content node的過程中，會略過DocumentType nodes, ProcessingInstruction nodes, Whitespace nodes, SignificantWhitespace nodes；如果目前node是一個content node的attribute，reader會傳回到這個attribute的owner element；MoveToContent的傳回類型是System.Xml.XmlNodeType，如果直到檔案末尾都沒找到合适的Node，傳回XmlNodeType.None；

while( XmlNodeType.None != reader.MoveToContent())

{

if(XmlNodeType.Element == reader.NodeType

&& reader.Name == "book")

{

MessageBox.Show(reader.ReadElementString());

}

 XmlTextReader在讀取Attribute的時候如果不移動指針就隻能得到Value不能得到Name

public int

SearchAttributes(string value, XmlReader reader)

{

if(!reader.HasAttributes)

return -1;

for(int ndx = 0;ndx<reader.AttributeCount;++ndx)

{

//既可以根據下标索引，也可以使用attribute name/local name + namespace URI來索引，例如reader["standalone"]

if(reader[ndx] == value)

return ndx;

}

return -1;

}

XmlTextReader可以通過MoveToAttribute/ MoveToFirstAttribute/ MoveToNextAttribute方法将指針從element移動到attribute；

public string

SearchAttributes(string value, XmlReader reader)

{

if(!reader.HasAttributes)

return string.Empty;

for(int ndx = 0;ndx<reader.AttributeCount;++ndx)

{

reader.MoveToAttribute(ndx);

if(reader.Value == value){

reader.MoveToElement();

return reader.Name;

}

reader.MoveToElement();

return string.Empty;

}

等效于

public string

SearchAttributes(string value, XmlReader reader)

{

if(!reader.MoveToFirstAttribute)

return string.Empty;

do{

if(reader.Value == value){

reader.MoveToElement();

return reader.Name;

}

}while(reader.MoveToNextAttribute());

reader.MoveToElement();

return string.Empty;

}

XmlTextReader在移動指針查找完Attribute後，最好調用MoveToElement確定指針回到Element的開始

XmlTextReader提供了多種讀取Element内容的方法：ReadString、ReadString、ReadBase64、ReadBinHex、ReadInnerXml、ReadOuterXml

ReadString在目前Node是Element的時候會組合内部所有的text, white space, significant white space, CDATA nodes組成一個String，但是組合的過程中不能遇到任何的markup；如果目前Node是text node，也組合前面所述的所有Node得到String，直到一個end tag或者markup；這個方法的傳回值如果為String.Empty，表示目前Node沒有可讀取的text或者目前Node不是Element/Text Node

string data =

@"<Root>Text data followed by mark up.<Child/></Root>";

StringReader str = new StringReader(data);

XmlTextReader reader = new XmlTextReader(str);

reader.WhitespaceHandling=WhitespaceHandling.None;

reader.MoveToContent();

MessageBox.Show("Content of Root: " + reader.ReadString());

ReadChars方法有三個參數，分别是目标位址，拷貝偏移，要拷貝的字元數，傳回實際讀取的字元數；本方法隻能工作在Element Node，不能工作于TextNode，這個方法主要用于分塊讀取一個Element中大量的資料；

ReadInnerXml和ReadOuterXml讀取一個element内所有的内容，使用string傳回，ReaderOuterXml傳回目前Node的start tag, content, 和end tag， ReadInnerXml隻傳回content；這兩個方法可以工作在Element Node和Attribute上；

ELEMENT XML POSITIONED ON ReadInnerXml ReadOuterXml

<author> <author> <fn>Ronnie</fn> <author>

<fn>Ronnie</fn> <ln>Yates</ln> <fn>Ronnie</fn>

<ln>Yates<ln> </ln>Yates</ln>

</author> </author>

ELEMENT XML POSITIONED ON ReadInnerXml ReadOuterXml

<auth fn="Ronnie"/> fn Ronnie fn="Ronnie"

XmlTextReader還支援Skip方法和Depth屬性

XmlTextWriter是單向的生成XML流的方法，同樣也不支援DTD；

XmlTextWriter writer = new XmlTextWriter("output.xml", Encoding.UTF8);

XmlTextWriter的Namespace屬性訓示是否支援Namespace，預設是支援；修改這個屬性必須在任何寫操作之前完成（WriteState必須是WriteState.Start）

XmlTextWriter writer = new XmlTextWriter("namespaces.xml");

writer.Namespaces = true;

writer.WriteElementString("po",

"test",

"http://www.fake.com");

Output

<po:test xmlns:po="http://www.fake.com" />

在開始寫入XML資料前，你必須設定XmlTextWriter的輸出格式，這通過Formatting屬性完成，可以設定成Formatting.Indented或Formatting.None；可以通過IndentChar和Indention屬性來設定縮進字元和縮進量；這些設定可以在任何時候進行，對後續的寫入操作生效；

XmlTextWriter使用WriteStartDocument來寫入XML declaration，這必須是構造函數之後的第一個寫入操作；

XmlTextWriter writer =

new XmlTextWriter("startdoc.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.WriteStartDocument(true);

writer.WriteElementString("root", null);

writer.WriteEndDocument();

writer.Close();

Output

<?xml version="1.0" encoding="utf-8" standalone="yes"?>

XmlTextReader提供WriteStartElement和WriteEndElement方法來逐漸寫入Element；WriteElementString用于一次性寫入隻含有text的element

XmlTextWriter writer =

new XmlTextWriter("startelem.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.WriteStartDocument();

// Make a true empty element

writer.WriteStartElement("root");

writer.WriteEndElement();

// Make an empty element with start and end tags， <root></root>

// writer.WriteStartElement("Empty");

// writer.WriteFullEndElement();

writer.Close();

Output

<?xml version="1.0" encoding="utf-8"?>

另一個例子

XmlTextWriter writer =

new XmlTextWriter("elementstring.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.WriteStartElement("StockQuote", "http://fakequote.com");

writer.WriteElementString

("Symbol", "http://fakequote.com", "MSFT");

writer.WriteElementString("Value",

"http://fakequote.com",

XmlConvert.ToString(123.32));

writer.WriteEndElement();

writer.Close();

Output

</StockQuote>

XmlTextWriter使用WriteStartAttribute和WriteEndAttribute方法來逐漸寫入Attribute；也支援WriteAttributeString來一次性寫入；

public static void Main()

{

XmlTextWriter writer =

new XmlTextWriter("startatt.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.WriteStartElement("root");

writer.WriteStartAttribute("po", "att1", "http://bogus");

writer.WriteString("value");

writer.WriteEndAttribute();

writer.WriteEndElement();

writer.Close();

}

Output

另一個例子

public static void Main()

{

XmlTextWriter writer =

new XmlTextWriter("attstring.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.WriteStartElement("root");

writer.WriteAttributeString("att1", "http://bogus", "value1");

writer.WriteEndElement();

writer.Close();

}

Output

WriteAttributeString也可以寫入特殊的XML Attribute——xml:space和xml:lang，前者決定Element内的空格如何處理（preserve、default），後者描述這個Element的内容是何種語言

public static void Main()

{

XmlTextWriter writer =

new XmlTextWriter("nsdecl.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.WriteStartElement("root");

// set the xml:space attribute to preserver

writer.WriteAttributeString("xml",

"space",

null,

"preserve");

// set the xml:lang attribute to lang:en

writer.WriteAttributeString("xml",

"lang",

null,

"en");

writer.WriteEndElement();

writer.Close();

}

Output

WriteAttributeString還可以用于聲明Namespace

public static void Main()

{

XmlTextWriter writer =

new XmlTextWriter("nsdecl.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.WriteStartElement("root");

// redefine the default namespace

writer.WriteAttributeString("xmlns",

null,

"http://default");

// define a namespace prefix "po"

writer.WriteAttributeString("xmlns",

"po",

null,

"http://post_office");

writer.WriteEndElement();

writer.Close();

}

Output

XmlTextWriter使用WriteString方法來一次性寫入内容字元串；如果需要多次寫入，使用WriteChars方法；WriteBase64和WriteBinHex用于寫入二進制資料；

XmlConvert提供了将.NET Compact Framework的類型轉換成XML Schema映射，也能将XML String轉換成.NET Compact Framework的類型，這比使用.NET自帶的ToString和System.Convert安全；

XmlTextWriter writer =

new XmlTextWriter("xmlconvert.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.Indentation = 2;

writer.WriteStartElement("root");

writer.WriteElementString("boolean",

XmlConvert.ToString(false));

writer.WriteElementString("Single",

XmlConvert.ToString(Single.PositiveInfinity));

writer.WriteElementString("Double",

XmlConvert.ToString(Double.NegativeInfinity));

writer.WriteElementString("DateTime",

XmlConvert.ToString(DateTime.Now));

writer.WriteEndElement();

writer.Close();

XmlTextReader reader = new XmlTextReader("xmlconvert.xml");

reader.WhitespaceHandling = WhitespaceHandling.None;

reader.MoveToContent();

reader.ReadStartElement("root");

bool b = XmlConvert.ToBoolean(reader.ReadElementString());

float s = XmlConvert.ToSingle(reader.ReadElementString());

double d = XmlConvert.ToDouble(reader.ReadElementString());

DateTime dt = XmlConvert.ToDateTime(reader.ReadElementString());

reader.Close();

MessageBox.Show("Boolean: " + b.ToString());

MessageBox.Show("Single: " + s.ToString());

MessageBox.Show("Double: " + d.ToString());

MessageBox.Show("DateTime: " + dt.ToString());

雜項：如果你先要向XmlTextWriter寫入Raw資料，使用WriteRaw方法；如果你想要寫入注釋，使用WriteComment方法；WriteCData方法會寫入CDATA Sections；使用WriteProcessingInstruction寫入處理指令；WriteWhitespace用于向XML内寫入空格；

public static void Main()

{

string rawText = "<bad_xml att=/"bad chars ='/"<>/">/n/t" +

"This is bad content — & < > = ' /"/n" +

"</bad_xml>";

XmlTextWriter writer =

new XmlTextWriter("xmlconvert.xml", Encoding.UTF8);

writer.Formatting = Formatting.Indented;

writer.Indentation = 2;

writer.WriteStartElement("root");

writer.WriteRaw(rawText);

writer.WriteEndElement();

writer.Close();

}

Output

This is bad content — & < > = ' "

</bad_xml></root>

.Net Compact Framework開發（3）——XML SAX操作

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