Tool Development 04 - XML

Tool Development
Chapter 04: XML
Nick Prühs

Assignment Solution #3
DEMO
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Objectives
• To get an overview of the structure of XML
documents in general
• To learn how to read and write XML documents in
.NET
• To understand advanced concepts of XML
processing such as XPath and XSLT
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XML Fundamentals
• Short for Extensible Markup Language
• Logical structuring of data
• Domain-specific languages
• Content-oriented markup (in contrast to HTML)
• Self-descriptive structure
• Tags
• XML Schema
• Structural variations (e.g. variable child node count)
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XML Benefits
• Human-readable
• Automated document validation
• Used in machine-machine communication (e.g.
web services)
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XML Document Example
XML (GraphML)
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<?xml version="1.0" encoding="UTF-8"?>
<graphml xmlns="http://graphml.graphdrawing.org/xmlns"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://graphml.graphdrawing.org/xmlns http://graphml.graphdrawing.org/xmlns/1.0/graphml.xsd">
<graph id="G" edgedefault="undirected">
<node id="n0"/>
<node id="n1"/>
<node id="n2"/>
<node id="n3"/>
<edge source="n0" target="n2"/>
</graph>
</graphml>

XML (Collada)
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<node id="here">
<translate sid="trans">1.0 2.0 3.0</translate>
<rotate sid="rot">1.0 2.0 3.0 4.0</rotate>
<matrix sid="mat">
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0
</matrix>
</node>

XML (XAML)
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<Window x:Class="LevelEditor.View.NewMapWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="New Map" Height="300" Width="300">
<StackPanel>
<DockPanel>
<TextBlock DockPanel.Dock="Left" Width="75" Margin="5">Map Width:</TextBlock>
<TextBox Name="TextBoxMapWidth" Margin="5">32</TextBox>
</DockPanel>
<DockPanel>
<TextBlock DockPanel.Dock="Left" Width="75" Margin="5">Map Height:</TextBlock>
<TextBox Name="TextBoxMapHeight" Margin="5">32</TextBox>
</DockPanel>
<DockPanel>
<TextBlock DockPanel.Dock="Left" Width="75" Margin="5">Default Tile:</TextBlock>
<StackPanel Margin="5" Name="DefaultTilePanel" />
</DockPanel>
<Button Click="OnCreateMapClicked">Create New Map</Button>
</StackPanel>
</Window>

XML Tree Structure
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Window
StackPanel
DockPanel
TextBlock TextBox
DockPanel
TextBlock TextBox
DockPanel
TextBlock StackPanel
Button

XML Node Types
• Elements
• Document Element
• Content
• Attributes
• Comment
• Namespaces
• Processing Instructions
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XML Elements
• Main parts of XML documents
• Boundaries defined by start and end tags
• Consist of name, attributes and content
• Can be nested
• Root element is called document element
• Always exactly one document element
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<node id="n0"/>
<node id="n1"/>
</graph>

XML Content
• Text between start and end tags of an element
• Either simple, complex or mixed
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<node id="n0"/>
<node id="n1"/>
</graph>

XML Attributes
• Associate name-value pairs with elements
• May appear within start tags, only
• Order doesn’t matter
• Unique per element
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<node id="n0"/>
<node id="n1"/>
</graph>

XML Comments
• Not part of document data
• XML processors may (but don’t need to) retrieve
text comments
• Double-hyphen (“- -”) must not occur within
comments
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XML Namespaces
• Used for distinguishing nodes with same names
• Bound to an URI by the xmlns attribute
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<graphml xmlns="http://graphml.graphdrawing.org/xmlns">
<node id="n0"/>
<node id="n1"/>
</graph>
</graphml>

Writing XML in .NET
• Abstract base class XmlWriter
• Non-cached
• Forward-only
• Write-only
• Writes to stream or file
• Verifies that the characters are legal XML characters
and that element and attribute names are valid
XML names
• Verifies that the XML document is well formed
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Creating an XmlWriter
• XmlWriter instances are created using the static
Create method
• XmlWriterSettings class is used to specify the set
of features you want to enable on the XmlWriter
object
• XmlWriterSettings can be reused to create
multiple writer objects
• Allows adding features to an existing writer
• Create method can accept another XmlWriter object
• Underlying XmlWriter object can be another XmlWriter
instance that you want to add additional features to
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Creating an XmlWriter
C#
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XmlWriterSettings settings = new XmlWriterSettings
{
Indent = true,
IndentChars = "t"
};
XmlWriter writer = XmlWriter.Create("books.xml", settings);

XmlWriterSettings Defaults
Property Description Default Value
CheckCharacters
Whether to do character
checking.
true
Encoding Type of text encoding to use. Encoding.UTF8
Indent Whether to indent elements. false
IndentChars
Character string to use when
indenting.
Two whitespaces
NewLineChars
Character string to use for line
breaks.
rn
NewLineOnAttributes
Whether to write attributes on a
new line.
false
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Writing XML
with the XmlWriter
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Member Name Description
WriteElementString Writes an entire element node, including a string value.
WriteStartElement Writes the specified start tag.
WriteEndElement Closes one element and pops the corresponding namespace scope.
WriteElementString Writes an element containing a string value.
WriteValue
Takes a CLR object and converts the input value to the desired output type using the
XML Schema definition language (XSD) data type conversion rules. If the CLR object is a
list type, such as IEnumerable, IList, or ICollection, it is treated as an array of the
value type.
WriteAttributeString Writes an attribute with the specified value.
WriteStartAttribute Writes the start of an attribute.
WriteEndAttribute Closes the previous WriteStartAttribute call.
WriteNode Copies everything from the source object to the current writer instance.
WriteAttributes Writes out all the attributes found at the current position in the XmlReader.

Writing XML Elements
C#
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{
Indent = true
};
using (XmlWriter writer = XmlWriter.Create("books.xml", settings))
{
// Write XML data.
writer.WriteStartElement("book");
writer.WriteElementString("title", "Awesome book");
writer.WriteElementString("price", "19.95");
writer.WriteEndElement();
}

Writing XML Attributes
C#
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{
Indent = true
};
{
// Write XML data.
// Write the genre attribute.
writer.WriteAttributeString("genre", "novel");
}

Namespace Handling
• XmlWriter maintains a namespace stack
corresponding to all the namespaces defined in the
current namespace scope
• WriteElementString, WriteStartElement,
WriteAttributeString and WriteStartAttribute
methods have overloads that allow you to specify a
namespace URI
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Namespace Handling
C#
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{
Indent = true,
IndentChars = "t"
};
{
// Write XML data.
// Write the namespace declaration.
writer.WriteAttributeString("xmlns", "bk", null, "http://www.example.com/book");
// Write the genre attribute.
writer.WriteAttributeString("genre", "novel");
}

Reading XML in .NET
• Abstract base class XmlReader
• Non-cached
• Forward-only
• Read-only
• Reads from stream or file
• Verifies that the XML document is well formed
• Validates the data against a DTD or schema
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Creating an XmlReader
• XmlReader instances are created using the static
Create method
• XmlReaderSettings class is used to specify the set
of features you want to enable on the XmlReader
object
• XmlReaderSettings can be reused to create
multiple reader objects
• Allows adding features to an existing reader
• Create method can accept another XmlReader object
• Underlying XmlReader object can be another XmlReader
instance that you want to add additional features to
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Creating an XmlReader
C#
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XmlReaderSettings settings = new XmlReaderSettings
{
IgnoreWhitespace = true,
IgnoreComments = true
};
XmlReader reader = XmlReader.Create("books.xml", settings);

XmlReaderSettings Defaults
Property Description Default Value
CheckCharacters
Whether to do character
checking.
true
IgnoreComments Whether to ignore comments. false
IgnoreProcessingInstructions
Whether to ignore processing
instructions.
false
IgnoreWhitespace
Whether to ignore insignificant
white space.
false
Schemas
XmlSchemaSet to use when
performing schema validation.
Empty XmlSchemaSet
ValidationType
Whether to perform validation or
type assignment when reading.
ValidationType.None
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Working with XmlReader
• Current node refers to the node on which the
reader is positioned
• Move through the data and read the contents of a
node
• Reader is advanced using any of the Read methods
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Reading XML Elements
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IsStartElement Checks if the current node is a start tag or an empty element tag.
ReadStartElement Checks that the current node is an element and advances the reader to the next node.
ReadEndElement Checks that the current node is an end tag and advances the reader to the next node.
ReadElementString Reads a text-only element.
ReadToDescendant Advances the XmlReader to the next descendant element with the specified name.
ReadToNextSibling Advances the XmlReader to the next sibling element with the specified name.
IsEmptyElement Checks if the current element has an empty element tag.
After the XmlReader is positioned on an element, the node properties, such as
Name, reflect the element values.

Reading XML Elements
C#
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using (XmlReader reader = XmlReader.Create("books.xml"))
{
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());
}

Reading XML Attributes
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After MoveToAttribute has been called, the node properties, such as Name, reflect
the properties of that attribute, and not the containing element it belongs to.
AttributeCount Gets the number of attributes on the element.
GetAttribute Gets the value of the attribute.
HasAttributes Gets a value indicating whether the current node has any attributes.
Item Gets the value of the specified attribute.
MoveToAttribute Moves to the specified attribute.
MoveToElement Moves to the element that owns the current attribute node.
MoveToFirstAttribute Moves to the first attribute.
MoveToNextAttribute Moves to the next attribute.

Reading XML Attributes
C#
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XmlReaderSettings settings = new XmlReaderSettings
{
IgnoreWhitespace = true
};
using (XmlReader reader = XmlReader.Create("books.xml", settings))
{
while (reader.Read())
{
if (reader.HasAttributes)
{
Console.WriteLine("Attributes of <" + reader.Name + ">");
while (reader.MoveToNextAttribute())
{
Console.WriteLine(" {0}={1}", reader.Name, reader.Value);
}
// Move the reader back to the element node.
reader.MoveToElement();
}
}
}

Reading Typed Data
• XmlReader class permits callers to read XML data and
return values as simple-typed CLR values rather than
strings
• Gets values in the representation that is most
appropriate for the coding job without having to
manually perform value conversions and parsing
• ReadContentAsBoolean, ReadContentAsDateTime,
ReadContentAsDouble, ReadContentAsLong,
ReadContentAsInt, and ReadContentAsString methods are
used to return a specific CLR object
• ReadElementContentAs method is used to read element
content and return an object of the type specified
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DOM vs. SAX Parsing
• Simple API for XML (SAX)
• Sequential access
• Required memory is proportional to maximum depth of
the input document
• Document validation requires keeping track of id
attributes, open elements, etc.
• Document Object Model (DOM)
• Operates on the document as a whole
• Required memory is proportional to the entire
document length
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Working with XmlDocument
• In-memory tree representation of an XML
document
• Enables navigation and editing of parsed
documents, including adding and removing nodes
• XmlNode object is the basic object in the DOM tree
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Working with XmlDocument
C#
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// Load XML document.
XmlDocument document = new XmlDocument();
document.Load("books.xml");
// Find book element.
XmlNode bookNode = document["book"];
// Add author element.
XmlElement element = document.CreateElement("author");
XmlText text = document.CreateTextNode("Nick Prühs");
bookNode.AppendChild(element);
element.AppendChild(text);
// Write document to console.
XmlWriter writer = new XmlTextWriter(Console.Out);
document.WriteTo(writer);

Navigating XML Documents
• XML Path Language (XPath) selects nodes from an
XML document
• Each expression is evaluated with respect to a
context node (e.g. “child”)
• Location path consists of a sequence of location
steps
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XPath Location Steps
• Axis
• Specifies the tree relationship between the nodes
selected by the location step and the context node
• Node test
• Specifies the node type and expanded-name of the
nodes selected by the location step
• Predicate(s)
• Further refine the set of nodes selected by the location
step
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XPath Axes
Axis
Ancestor Selects all ancestors (parent, grandparent, etc.) of the current
node.
Ancestor-or-self Selects all ancestors (parent, grandparent, etc.) of the current
node and the current node itself.
Attribute Selects all attributes of the current node.
Child Selects all children of the current node.
Descendant Selects all descendants (children, grandchildren, etc.) of the
current node.
Descendant-or-self Selects all descendants (children, grandchildren, etc.) of the
current node and the current node itself.
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XPath Axes
Axis
Following Selects everything in the document after the closing tag of
the current node.
Following-sibling Selects all siblings after the current node.
Namespace Selects all namespace nodes of the current node
Parent Selects the parent of the current node.
Preceding Selects all nodes that appear before the current node in the
document, except ancestors, attribute nodes and namespace
nodes.
Preceding-sibling Selects all siblings before the current node.
Self Selects the current node.
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XPath Node Tests
• node() is true for any node of any type
• * is true for any node of the principal node type.
• child::* will select all element children of the context
node
• attribute::* will select all attributes of the context
node
• comment() is true for any comment node
• text() is true for any text node
• processing-instruction() is true for any
processing instruction
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XPath Predicates
Restrict a node-set to select only those nodes for which some
condition is true.
Example:
book[@genre=‘scifi’]
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XPath Location Paths
Location step syntax:
axis::nodetest[predicate]
Example:
/books/book/attribute::*
/books/book[@genre=‘scifi’]
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XSLT Fundamentals
• Short for Extensible Stylesheet Language
Transformation
• Transforms XML documents into other formats
such as other XML documents, HTML or plain text
• Turing-complete
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XSLT Processing
1. Read stylesheet file.
2. Build source tree from input XML document.
3. For each node in the source tree:
1. Process source tree node.
2. Find best-matching template in the stylesheet.
3. Evaluate the template contents.
4. Create node(s) in the result tree.
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Common XSLT Elements
Node Description
xsl:apply-templates Specifies that other matches may exist
within that node. If “select” is specified,
only the templates that specify a match
that fits the selected node or attribute
type will be applied.
xsl:choose Contains xsl:when blocks and up to one
xsl:otherwise block.
xsl:for-each Creates a loop which repeats for every
match.
xsl:stylesheet Top-level element. Occurs only once in a
stylesheet document.
xsl:template Specifies processing templates.
xsl:value-of Outputs a variable.
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XSLT Example
XML
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<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet href="books.xsl" type="text/xsl" ?>
<books>
<book>
<title>Awesome book</title>
<price>19.95</price>
</book>
<book>
<title>Another book</title>
<price>9.95</price>
</book>
</books>

XSLT Example
XSLT
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<xsl:stylesheet
version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns="http://www.w3.org/1999/xhtml">
<xsl:output method="xml" indent="yes" encoding="UTF-8"/>

XSLT Example
XSLT
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<xsl:template match="/books">
<html>
<head>
<title>Transforming books.xml with XSLT</title>
</head>
<body>
<h1>Books</h1>
<table>
<tr>
<th>Title</th>
<th>Price</th>
</tr>
<xsl:apply-templates select="book">
<xsl:sort select="title" />
</xsl:apply-templates>
</table>
</body>
</html>
</xsl:template>

XSLT Example
XSLT
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<xsl:template match="book">
<tr>
<td>
<xsl:value-of select="title"/>
</td>
<td>
<xsl:value-of select="price"/>
</td>
</tr>
</xsl:template>

XSLT Example
Rendered HTML
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OpenFileDialog Control
Common dialog box that allows a user to specify a
filename for one or more files to open.
Rendered View
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OpenFileDialog Control
C#
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// Show open file dialog box.
OpenFileDialog openFileDialog = new OpenFileDialog
{
AddExtension = true,
CheckFileExists = true,
CheckPathExists = true,
DefaultExt = ".txt",
Filter = "Text files (.txt)|*.txt",
ValidateNames = true
};
var result = openFileDialog.ShowDialog();
if (result != true)
{
return;
}
// Open text file.
using (var stream = openFileDialog.OpenFile())
{
// Do something.
}

SaveFileDialog Control
Common dialog that allows the user to specify a
filename to save a file as.
Rendered View
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SaveFileDialog Control
C#
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// Show save file dialog box.
SaveFileDialog saveFileDialog = new SaveFileDialog
{
AddExtension = true,
CheckPathExists = true,
DefaultExt = ".txt",
FileName = "TextFile",
Filter = "Text files (.txt)|*.txt",
ValidateNames = true
};
var result = saveFileDialog.ShowDialog();
if (result != true)
{
return;
}
// Open file stream.
using (var stream = saveFileDialog.OpenFile())
{
// Do something.
}

Assignment #4
1. Save Map
1. Add a new MenuItem “Save As” to your MainWindow,
along with a ToolBar button with tooltip.
2. Allow saving a map file by showing a Save File Dialog
when the Save As command is executed.
1. Map files should be well-formed, valid XML files.
2. Each map file should contain the width and height of the
map, as well as the types of all map tiles.
3. It should not be possible to save a map if there is
none.
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Assignment #4
2. Load Map
1. Add a new MenuItem “Open” to your MainWindow,
along with a ToolBar button with tooltip.
2. Add separators to both your toolbar and menu.
3. Allow loading a map file by showing an Open File
Dialog when the Open command is executed.
4. Opening a corrupt or invalid XML file should result in
an error message. The current map should only be
discarded of the map file could be successfully
opened.
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References
• MSDN. XML Documents and Data.
http://msdn.microsoft.com/en-
us/library/2bcctyt8%28v=vs.110%29.aspx, May 2016.
• Luttenberger. Internet Applications – Web Services Primer.
Department for Computer Science, CAU Kiel, 2008.
• Brandes, Eiglsperger, Lerner. GraphML Primer.
http://graphml.graphdrawing.org/primer/graphml-primer.html,
May 2016.
• Barnes, Finch. COLLADA – Digital Asset Schema Release 1.5.0
Specification. Sony Computer Entertainment Inc., April 2008.
• Clark, DeRose. XML Path Language (XPath).
http://www.w3.org/TR/xpath/, November 16, 1999.
• w3schools.com. XPath Axes.
http://www.w3schools.com/xsl/xpath_axes.asp, May 2016.
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Thank you!
http://www.npruehs.de
https://github.com/npruehs
@npruehs
dev@npruehs.de

5 Minute Review Session
• What are the main benefits of using XML?
• What are the three main XML processing steps?
• Which XML node types do you know?
• How do you properly create XmlWriter instances?
• How do you read typed XML content?
• What is the difference between DOM and SAX
parsing?
• What are the main parts of an XPath location step?
• What is XSLT and how does it work?
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Tool Development 04 - XML

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