It had been leaked before, but last week Microsoft confirmed that Windows Phone 7 Series will use Silverlight and XNA as its primary technologies for developing applications. It has also been made known that previous Windows Mobile applications will not work on WP7S devices. With Silverlight being one of the primary development technologies I’ve seen lots of messages from developers in forums that are evaluating the technology and overall from what I’ve seen opinions are mixed. Some see Silverlight as being advantageous while others see it is being a simple technology for making simple applications. While not yet confirmed it appears that Silverlight and XNA will be the only technologies that Application developers will be able to use for WP7S development while native development will be reserved for OEM use. Do these changes have a positive or negative impact on Windows Phones?

So far I think it will have a positive impact. It contributes to bringing Windows Phones from at times appearing to being a neglected product to being aligned and based off of a technology that Microsoft is strongly supporting. I want to emphasize the positive impacts that Silverlight will have. It’s difficult to start looking at the full picture of what Silverlight will bring to Windows Phones before Microsoft discloses more specific information (such as how phone specific features would be accessed from Silverlight or how simultaneous tasks are managed) so I’m basing my view on what’s known about Silverlight so far. After Mix I may revisit this topic.

I’ve got no doubt that there will be some other developers that will transition to other development technologies or other platforms. But the transition won’t be in one direction. There are a number of developers that have already been developing applications using XNA and Silverlight and I believe that some of these developers will transition into Windows Phone development. New developers coming to the platform will also find the development environment to be more consistent and welcoming than the previous environment. Developers that have used other .Net technologies will also find that they can transfer some of their knowledge to Silverlight development.

I’ve been using Silverlight for developing applications within Enterprise organizations since last year. Despite being one of the younger .Net based technologies (Silverlight 1.0 was released in April 2007) it’s quickly evolved over the past few years. The first two versions of Silverlight ran within a browser (IE, Safari, FireFox) but as of Silverlight 3 developers gained the ability to make applications that run outside of the browser. Silverlight 3 applications currently run on Windows and OS X based machines. Silverlight 2 applications run on Windows, OS X, and Linux (through Moonlight ). With Silverlight 4 the technology gains the ability to act outside of its sandbox. Its capabilities are also expanded to have native support for other devices (webcams, printers, enhanced media capabilities) and gets support for Google Chrome.

One of the prevailing complaints about building user interfaces with Windows Mobile was that the control set looked a little dated; its style was consistent with what you’d expect to see from Windows 95. It was possible to make your own controls to meet your needs but even for some simple scenarios this could mean rebuilding a control from the ground up. By consequence unless a developer made extra effort to improve upon the control set or purchased a better looking third party control set his or her applications would also look like they were inspired by Windows 95.

Windows Mobile form designer with button in Visual Studio.

Silverlight by contrast has a control set that is much more visually appealing, renders consistently across platforms, and more easily adapted to needs. If you find that a control doesn’t fit the visual style that you are aiming for then you can replace the controls template to change its appearance instead of completely rebuilding the control. The Silverlight controls can be combined in ways that one can’t easily do using the other UI technologies.

Silverlight Designer with button in Expressions Blend.

If you’ve ever used a technology that allows you to build your interfaces declaratively then you’ve already seen the advantages it brings. You can create interfaces quickly and usually someone without a full programming skill set can pick up on a declarative language to make changes on their own. HTML is one ubiquitous declarative UI technology. One can either type out tags and elements to describe how things should appear on the screen or use a visual tool to edit the HTML. Something else (in the case of HTML the browser) will interpret the information and use it to create the final interface. Several technologies that use declarative interfaces are also supported through third party tools so that someone can manipulate the interface visually without being exposed to the language. Declarative UIs usually have separation of the UI and code; so a person acting as a designer can edit such interfaces without touching the code associated with the interface. Until now there has been no declarative interface technologies offered by Microsoft for Windows Mobile.

In a Silverlight project the UI is stored in XAML files. The code is saved in a C# or VB file.

Silverlight UIs are usually built declaratively, though this isn’t mandatory. Silverlight’s declarative language (XAML) is XML based and at first glance one can see the similarities between editing XAML and editing HTML. Once a developer or designer learns XAML or learns to use an XAML editor (such as Expressions Blend  ) he or she should be able to build complex interfaces with less effort than what would be required to build the interface with previous technologies.

A button containing a checkbox and the XAML used to create it in Expressions Blend.

Animations, transitions, and media are supported much better in Silverlight than they are in most other UI technologies. Transitions can be created declaratively in the same XAML that one uses to define an interface or in code. One can make animate an elements position, opacity, colour, and apply pixel shaders when making a transition (and yes, Silverlight will take advantage of a device’s graphic acceleration capabilities when rendering elements). Silverlight’s support for media formats  include MP3, MP4, variations of WMV, and several others.

Netflix streaming to PC uses Silverlight. You can usually right-click on an interface and look for a Silverlight context menu to see if a an interface is Silverlight based.t

So far I've only looked on the surface of what Silverlight brings to WP7S since at this time in depth information is available. Mix 2010 is only 8 days away. While I won't be able to attend the MIX sessions are usually available through The Mix Site through Silverlight Streaming and I expect to know a lot more after the event. I'm hoping to hear that Microsofts plans for the entire Windows Phone 7 Series programming experience to equally compliment what I've experienced in Silverlight development so far.