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This chapter is from the book

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.

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 hardware-accelerated 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).

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 x 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.


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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