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Windows Presentation Foundation (WPF)
Windows Presentation Foundation (formerly code named Avalon) is a collection of
display technologies—or a display level subsystem—that allows developers to
take advantage of the latest graphic card hardware acceleration features. WPF
is the father of XAML; it is what allows the XAML language to be used in a
declarative way. The term declarative means “to describe” so XAML allows you to
describe your applications UI functionality and components.
Through learning Expression Blend and a little .NET code, you will have the
ability to compile your solutions into either a Silverlight or desktop
deliverable. Technically, there are slight differences to some of the methods
you use, but for the most part you will understand how both Silverlight and
executable-based WPF applications are created.
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By: Brennon Williams
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Reproduced from the book
Microsoft Expression Blend Unleashed
. Copyrightã 2008, Pearson Education, Inc., 800 East 96th Street, Indianapolis,
IN 46240.
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Silverlight enables your applications to be viewed in a browser-hosted
environment like Internet Explorer on any operating system that has the
Silverlight plug-in installed. This gives the user the same experience they
would get if they were using your application from a compiled .exe file running
on a Windows desktop—or so the theory goes. There is some reduced functionality
in Silverlight, such as the ability to create hardwareaccelerated 3D visuals
for example, so care must be taken to understand the construct you are
ultimately deploying to and the users you are working for.
Microsoft describes WPF as “a unified API, allowing developers to present high
definition media content from within their application constructs, as well as
providing extensibility to the .NET Framework for Vista specific technologies.”
This, in reality, means that the best of both WINForms applications and web
applications are available to you in WPF applications running on either Windows
Vista or Windows XP (with Service Pack 2 and the .NET Framework 3.0/3.5
installed).
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It has long been a nightmare for the UI Developer to ensure that content and
visual assets were being managed in terms of layout. Before a generic entry
level set of graphic cards (8Mb) came along, changing screen resolutions and
color settings all pointed to early retirement for a vast number of us. Things
have been getting better, certainly since .NET came along. Now WPF has once and
for all sorted out such issues; never before has it been so easy to create an
application that can adapt its content layout entirely based on the runtime
environment.
I am writing this book on a laptop with a 17" widescreen display running a
resolution of 1920 × 1200. Even though it is one of the most powerful laptops
on the market, some of the biggest companies in the world have managed to
produce software that does not layout correctly on it. One of the biggest joys
I have found in creating applications with Blend is that the layouts
work—perfectly every time.
It may take a little while to get your head around using Blend because most of
the time you no longer need to specify a control’s width and height. You are
now working with dynamic flow and elements layout and positioning that is based
on relevance to its parent and the construct it (the parent) provides. You can
still specify width and height, but in most cases this will be a minimum width
and a minimum height value. See Chapter 5, “UIElement: Control Embedding” for
detailed information.
Silverlight
Microsoft unveiled the plans for Silverlight in the second quarter of 2007.
Along with Silverlight comes the promise of a cut down, cross platform CLR
plug-in that would make creating and distributing XAML-based applications
across differing operating systems and devices simple. At the time of writing,
Microsoft has just released a preview version of Expression Blend 2.5, which
also showed the intended functionality that Blend will be providing in future
for this new technology.
Silverlight delivers a subset of the WPF core and will allow loose XAML-based
applications to run as pseudo web-based application or WBA. You can write the
functionality for your application in your choice of .NET-compliant languages
and/or JavaScript. So, Silverlight applications differ completely from another
type of Internet-delivered XAML application called an XBAP.
XBAP applications run as a compiled application in a browser that supports
additional features such as 3D, where Silverlight applications don’t. There are
many more differences that will change before the final incarnation of both
these technologies are ratified.
In either scenario, though, you must consider that when your application
(Silverlight or XBAP) runs in a browser type environment, it is running in what
is known as a partial trust sandbox. In geek speak, that means the application
is not installed on the end user’s machine (although the plugins and other
delivery mechanisms are).
Partial trust has some rules that you must follow. It is essential that you be
aware of your application requirements before deciding to try and deploy your
application in this manner, in either format. The rules are simple rules that
govern whether an application is able to run based on the user authentication
level and assigned roles or code privilege that is required by certain tasks,
controls, and objects.
The essence of the partial trust sandbox is that it has been developed using the
same security model that is available to all .NET developers using Code Access
Security (CAS). This means that varying levels of an “application code” can
demand and must obtain the correct security privileges before that code can
execute.
In the XBAP deployment scenario, you will find tight controls on File read and
write permissions and registry actions, as well as the inability to call and
execute most areas of unmanaged code. From an application-specific point of
view, you can’t launch new windows from your application. You can’t have
application-defined dialogs present; you can’t even apply BitmapEffects within
your application. However, at the time of writing, the biggest concern is that
you can’t access all the features of Windows Communication Foundation Web
Services. In other words, you are still restricted to only using data from
within the same executing domain. Undoubtedly, Microsoft is working very hard
to change these restrictions, and you should always seek the latest information
from Microsoft with regards to such restrictions.
I have described what has been slated at the time of this writing. Be sure to
check with Microsoft to see if any of the restrictions have been lifted, or if
more have been added. It’s all about security, so it is important to understand
it.
There are still many areas within an application that can run without issue, so
don’t be put off by the restrictions. Instead, look at it as a greater
challenge to your initiative. After all, you can still incorporate 2D, 3D, and
full animations in XBAPs, 2D in Silverlight, and image and audio features, flow
documents and much more in XAML-based offerings—not to mention that your
controls are no longer the clunky old CLR based controls.
Silverlight is exciting and it’s fast. By learning Expression Blend and a little
.NET development you will be able to create rich Internet applications (RIAs)
that will become a standard in future development scenarios.
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