Wednesday, August 20, 2008

Extensible Application Markup Languag (XAML)

Extensible Application Markup Language


Extensible Application Markup Language (XAML, pronounced zammel () is a declarative
XML-based language created by Microsoft which is used to initialize structured
values and objects. It is available under Microsoft's Open Specification Promise.
The acronym originally stood for Extensible Avalon Markup Language - Avalon
being the code-name for Windows Presentation Foundation (WPF).


Overview


XAML is used extensively in .NET Framework 3.0 technologies, particularly Windows
Presentation Foundation (WPF) and Windows Workflow Foundation (WF). In WPF,
XAML is used as a user interface markup language to define UI elements, data
binding, eventing, and other features. In WF, workflows can be defined using
XAML.


XAML elements map directly to Common Language Runtime object instances, while
XAML attributes map to Common Language Runtime properties and events on those
objects. XAML files can be created and edited with visual design tools such
as Microsoft Expression Blend, Microsoft Visual Studio, and the hostable Windows
Workflow Foundation visual designer. They can also be created and edited with
a standard text editor, a code editor such as XAMLPad, or a graphical editor
such as Vectropy.


Anything that is created or implemented in XAML can be expressed using a more
traditional .NET language, such as C# or Visual Basic.NET. However, a key aspect
of the technology is the reduced complexity needed for tools to process XAML,
because it is based on XML. As a result, a variety of products are emerging,
particularly in the WPF space, which create XAML-based applications. As XAML
is simply based on XML, developers and designers are able to share and edit
content freely amongst themselves without requiring compilation. As it is strongly
linked to the .NET Framework 3.0 technologies, the only fully compliant implementation
as of today is Microsoft's[citation needed].


Technology


A XAML file can be compiled into a .baml (Binary XAML) file, which may be inserted
as a resource into a .NET Framework assembly. At run-time, the framework engine
extracts the .baml file from assembly resources, parses it, and creates a corresponding
WPF visual tree or workflow.


When used in Windows Presentation Foundation, XAML is used to describe visual
user interfaces. WPF allows for the definition of both 2D and 3D objects, rotations,
animations, and a variety of other effects and features.


When used in Windows Workflow Foundation contexts, XAML is used to describe
potentially long-running declarative logic, such as those created by process
modeling tools and rules systems. The serialization format for workflows was
previously called XOML, to differentiate it from UI markup use of XAML, but
now they are no longer distinguished. However, the file extension for files
containing the workflow markup is still "XOML".


Templates


XAML uses a specific way to define Look and feel called Templates, different
from the Cascading Style Sheets syntax, but closer to XBL.


Example


This Windows Presentation Foundation example shows the text "Hello World!"
in the top-level XAML container called Canvas.


<Canvas xmlns="http://schemas.microsoft.com/client/2007"


xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

<TextBlock>Hello World!</TextBlock>

</Canvas>


The schema (the xmlns="http://schemas.microsoft.com..."
part) may have to be changed to work on your computer. Using a schema that Microsoft
recommends, the example can also be


<Canvas xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation">

<TextBlock>Hello World!</TextBlock>

</Canvas>


This can be integrated into a web page if WPF is installed using XBAPs (XML
Browser Applications) which are compiled applications running in a sandboxed
environment hosted within the browser. Another way is to use the Silverlight
plugin. The code can not be included directly in an html page; rather it must
be loaded into the page via JavaScript. If .NET 3.0 or later is installed, loose
XAML files can also be viewed on their own in a compatible web browser (including
Internet Explorer and FireFox) in conjunction with the .NET Framework 3.0, without
the need for the Silverlight plugin. Loose XAML files are markup-only files
limited to defining the visual content to be rendered. They are not compiled
with an application.


<html xmlns="http://www.w3.org/1999/xhtml">

<head>

<title>XAML Example </title>

<script type="text/javascript" src="MySilverlight.js"
/>

<script type="text/javascript" src="Silver.js" />

</head>

<body>

<div id="MySilverlight" >

</div>

<script type="text/javascript">

createMySilverlight();

</script>

</body>

</html>


The MySilverlight.js file must contain the code that loads the above XAML code
(as an XML file) under the MySilverlight html element.

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