MSDN Magazine - August 2008 - (Page 19)

There are a number of places in the BCL where you can find duplicated functionality. Sometimes the functionality is duplicated within the BCL itself—such is the case with generic collections and non-generic collections. Sometimes the functionality already exists in the base OS, as in the case of globalization support. Not only is it unnecessary to support every alternative in the Silverlight BCL, but we also can provide wins in performance and consistency by eliding this duplicated behavior. Since we introduced support for generic collections in version 2.0 of the .Net Framework, we’ve been advocating that people move to generics. In version 1.x of the runtime, general-purpose data structures had to be based on objects so that the same core data structure class could be used to create collections of different types. With generic-type parameters, the compiler is able to extend these general-purpose data structures to provide type safety, making code easier to write and maintain. Additionally, generic collections generally perform better on value types than non-generic collections because there’s no need to box items. Overall, generics provide all the functionality that non-generic collections provide. And because the duplication is unnecessary, we don’t include nongeneric collections like ArrayList in the Silverlight BCL. Everyone is familiar with at least some of the problems of globalization: many European cultures use a comma as a decimal point; in Chinese numbers are grouped into fours (1000,0000), and so forth. The .NET Framework implements globalization functionality internally so it can work properly in multiple cultures. To do this, it includes globalization data for all supported cultures, allowing .NET–targeted applications to behave consistently across all supported versions of Windows. There are drawbacks, however. The CLR must include large data tables, and the data often becomes stale over time. In addition, the data is Windows-centric, so the data for some .NET cultures is different for the same cultures in Mac OS X. For these reasons, the CoreCLR does not include its own globalization data. Instead, System.Globalization.CultureInfo uses the globalization functionality provided by the host OS. Thus, Silverlight applications will behave more like Mac applications on Mac OS X and like Windows applications on Windows. Overall we’ve tried to maintain a similar API surface area among the CLR, the .NET Compact Framework, and Silverlight, but there are other small differences scattered throughout the BCL. For example, because Silverlight has a single UI thread, it has a single Dispatcher object that holds a queue of work items for the UI. Using the Dispatcher will allow you to update the UI from a non-UI thread. This code will allow you to update a UI element— MyListBox—with a collection created on another thread (say, from a background thread): MyListBox.Dispatcher.BeginInvoke(() => MyListBox.ItemsSource = MyItems); Framework releases. A good example of this is isolated storage, which provides a virtualized file system to sandboxed applications. It’s been around since the .NET Framework 1.0, but it has always We introduced support for generic collections in Silverlight 2. addressed limited scenarios. Silverlight focuses on sandboxed applications and thus can make full use of isolated storage: using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication()) { using (StreamWriter writer = new StreamWriter(isoStore)) { writer.Write(“This is an isolated storage file.”); } } Like cookies in a Web browser, isolated storage allows Silverlight applications to maintain state across invocations. However, isolated storage offers a full virtualized file system that supports creation of directories and files. Although isolated storage is not intended for storage of high-value data such as passwords, the storage loca- We recommend using System.ComponentModel.BackgroundWorker in Silverlight because it encapsulates the updating of the UI on completion, but for compatibility we still include low-level threading APIs such as System.Threading.ThreadPool.QueueUserWorkItem and System.Threading.Monitor.Enter. Like the Security Transparency model, some functionality that is new in the Silverlight BCL actually appeared in previous .NET msdnmagazine.com August 2008 19 http://microsoft.net http://www.ektron.com/msdn http://microsoft.net http://msdnmagazine.com

Table of Contents Feed for the Digital Edition of MSDN Magazine - August 2008

MSDN Magazine - August 2008 Toolbox CLR Inside Out Basic Instincts Cutting Edge Patterns in Practice Data 2.0 - Expose And Consume Data In A Web Services World Biztalk EDI - Build A Robust EDI Solution With BizTalk Server Silverlight - Create Animations With XAML And Expression Blend Write On! - Create Web Apps You Can Draw On With Silverlight 2 Wicked Code - Craft Custom Controls For Silverlight 2 Team System Foundations Windows With C++ Concurrent Affairs Going Places { End Bracket }

MSDN Magazine - August 2008

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