Table 1. A comparison between Silverlight and WinRT apps.

Table 2. Silverlight versus WinRT app files and isolated storage.

I'll break these down into three groups: isolated storage, special folders (such as Documents and Pictures) and local files located anywhere on the hard disk drive (HDD).

For isolated storage, you'll quickly find that there are no differences between Silverlight and the Windows Runtime. A user can create, read, update or delete anything, as in Silverlight. The API for saving the files to isolated storage has changed slightly, but you still have free access to do anything in your sandboxed application.

For special folders, including Documents, Pictures and so on, you have the ability to prompt the user in a WinRT app by using a File or Folder Picker API, or write directly to these folders by specifying them in the Application Manifest.

For any other file or folder located on the local HDD, you have the ability in a WinRT app to write to it through the File and Folder Picker APIs. You can't write to a folder (such as C:\Temp\) in WinRT apps without first prompting the user. (In Silverlight 5, by contrast, you could use full trust to write to that folder without user intervention.)

6. Navigation: No More URI
In Silverlight applications, you typically use NavigationService.Navigate and pass it to a URI to navigate to a new page, like so:

this.NavigationService.Navigate(new Uri("/Page1.xaml", UriKind.Relative));

You can also implement more sophisticated application naviga­tion by using the Frame and Page controls. Page controls represent discrete sections of content, while the Frame acts as a container for Page controls and facilitates navigation to pages.

The Frame control usually uses the UriMapper to navigate to a new page in XAML, rather than codebehind. Here's a sample of the Frame control as well as the UriMapper (both of these reside in the System.Windows.Navigation namespace):

 <navigation:Frame x:Name="ContentFrame" 
  Style="{StaticResource ContentFrameStyle}" 
  Source="/Home" Navigated="ContentFrame_Navigated" NavigationFailed="ContentFrame_NavigationFailed" >
   <navigation:Frame.UriMapper >
     <uriMapper:UriMapper >
       <uriMapper:UriMapping Uri="" MappedUri="/Views/Home.xaml"/ >
       <uriMapper:UriMapping Uri="/{pageName}" 
        MappedUri="/Views/{pageName}.xaml"/ >
     </uriMapper:UriMapper >
   </navigation:Frame.UriMapper >
   </navigation:Frame >

WinRT apps still have the concepts of Frame and Page classes. The Frame is responsible for navigation and determining if you can navigate, go back or go forward to a page. You can create a new page by using one of the built-in templates and navigate to it by calling the following:

this.Frame.Navigate(typeof(NewPage));

Of course, this is generally more helpful if you can pass data to the page to which you're navigating. For example, if you had a TextBox named tb1 and wanted to pass the contents of it to another page, you could use the following code:

this.Frame.Navigate(typeof(NewPage), tb1.Text);

When the new page loads, you can retrieve the contents of the tb1.Text in the OnNavigatedTo event.

7. Controls
Silverlight controls such as Calendar, ChildWindow, DataGrid, DataPager, DescriptionViewer, MultiScaleImage, OpenFileDialog, RichTextBox, SaveFileDialog, TabControl, TabItem, TreeView, Validation and WebBrowser are no longer present in the Windows Runtime. Instead, Microsoft has replaced some of them with controls that interact with touch devices more easily. Here's a list of the most important ones:

• ListView displays a collection as a stack of items.
• GridView is used for grid-based layouts and grouping of items.
• Semantic Zoom allows you to zoom in or zoom out on a collection.
• FlipView is an items control that displays one item at a time.
• Media Player is similar to the MediaElement in Silverlight, but now has built-in playback buttons.
• Progress Ring is a progress indicator with a circular motion.
• Application Bar is typically used to replace menus.
• CarouselPanel, RichTextBlock and WrapGrid are a few other new controls you may find beneficial in your next WinRT app.

Many of these new controls can be found in Figure 3.

[Click on image for larger view.]

Figure 3. Some of the new WinRT app controls.

8. Animations
Animations are a key component of the new Windows UI. After logging into Windows 8 you'll see animated live tiles that display information such as new e-mails, the weather, trending news topics and so on. Opening an application launches an animation. When a user adds or removes an item inside an app, an animation might appear. In short, animations are everywhere in Windows 8, so it makes sense that Microsoft baked animations into the Windows Runtime.

Animation Easing in Silverlight allows you to apply built-in animation functions to your Silverlight controls. The result is a variety of animation effects that make your controls move in a more realistic way. The only issue with this is that few people are interested in Silverlight animations, as Windows XP and Windows 7 don't have the "fast and fluid" feel of Windows 8.

WinRT apps have a built-in animation library provided out of the box. It includes a variety of animations such as page and content transitions, as well as many others that you can see here.

Note that there are two types of WinRT animation:

• Theme transitions animate loading, unloading or changing screen location.
• Theme animations are built to run on user interaction; you must trigger them.

You can also create custom animations if the supplied animations don't fit your needs. I haven't yet found a case for building my own animations.

9. Charms
Charms allow you to have everything at your finger ­tips without going through a whole lot of effort. With a swipe to the right-hand side of the screen you can bring up the Charms bar, which allows you to do things like create Search contracts to allow your application to integrate with the built-in Windows Search.

You can also make use of the Share contract to share content in your application with other apps. For instance, a user that has opened an RSS reader might want to share a link with her friends; this can be done easily with this built-in contract. Many other examples can be found at here. This functionality was missing completely from Silverlight applications, as they were sandboxed inside a Web browser -- you'd have to write code for similar functionality.

10. Monetization
One of the best features of Windows 8 is the built-in marketplace, which is designed for app discovery and reach. One problem that plagued Silverlight developers was an inability to find customers for their applications. The Windows Store already has 231 global markets (at the time of this writing) available to discover and purchase your app.

There's also a solution for customers wanting to deploy their WinRT app to their internal infrastructure, as well as a flexible business model (free, paid or trial) for those wanting public discovery of an application. The Microsoft Advertising SDK is also available if you want to give your app away and make money off of ad impressions.

There's a low barrier to entry, as the registration fee is $49 for individuals and $99 for companies. Microsoft shares up to 80 percent of the revenue generated from app sales, providing even more incentive for developers.

Only the Start
These 10 items are only the start. As you begin building your application, you'll likely find other differences between the Windows Runtime and Silverlight. The good news is that the Windows 8 community is thriving, and many folks are blogging and helping others understand this new platform. Microsoft has also provided excellent guidance about the way apps should look and feel, as well as plenty of sample source code. So what are you waiting for? Go ahead and begin building your first WinRT app!