WPF: A Beginner's Guide Series  By Sacha Barber

1.  WPF: A Beginner's Guide - Part 1 of n

An introduction into the WPF layout system .

2. WPF : A Beginners guide part 2 of n

An introduction into XAML / code and WPF resources .

3. WPF : A Beginners guide part 3 of n

An introduction into RoutedEvents / RoutedCommands .

4. WPF: A Beginner's Guide - Part 4 of n

An introduction into WPF Dependancy Properties .

5. WPF: A Beginner's Guide - Part 5 of n

Part 1: Introduction

Chapter 1. Introducing Silverlight 2


Silverlight is Microsoft's new browser-based plug-in for delivering richer interactive applications to users over the web. Silverlight 2 is Microsoft's second release of the Silverlight platform. Silverlight 2's biggest change from Silverlight 1.0 is the inclusion of a compact version of the .NET Framework, complete with the .NET Framework 3.0 Common Language Runtime. By adding .NET to Silverlight, Microsoft makes it easy for .NET developers to reuse their existing programming skills, collaborate with designers, and quickly create rich applications for the Web.

And even though Silverlight 2 brings .NET to the client, it can be integrated easily with many existing Web technologies and backend Web platforms. That means Silverlight will integrate with your existing infrastructure and applications, from IIS and .NET to Apache and PHP to simple JavaScript and XHTML on the client. Silverlight is not a tool meant for exclusive use on ASP.NET web sites, which should result in broader adoption of the new technology.

Still, one of the key benefits of Silverlight 2 is that it can execute any .NET language, including C# and VB.NET. Unlike the CLR included with the "normal" .NET Framework, multiple instances of the core "Silverlight CLR" can be hosted in a single process. With this, the layout markup in the Silverlight XAML file (.xaml file) can be augmented by code-behind code with all programming logic written in any .NET language.

Silverlight 2 ships with a "lightweight" version of the full .NET Framework, which features, among other classes, extensible controls, XML Web Services, networking components, and LINQ APIs. This class library is a subset of (and is considerably smaller than) the .NET Framework's Base Class Library, which enables the Silverlight plug-in to be a fast and small download. For security, all Silverlight code runs in a sandbox environment that prevents invoking platform APIs, protecting user computers from malicious code. Silverlight 2 also adds support for DRM in media files, a fact that will make some people happy and others cringe.

In addition to the .NET Framework classes, Silverlight 2 also ships with a subset of the WPF UI programming model, including support for shapes, documents, media, and WPF animation objects. The Silverlight 2 December CTP did not ship with many WPF UI controls, though, so out-of-the-box controls will remain limited until beta 1. The Silverlight 2 beta 1 release promises to deliver more controls as well as the ability to bind to data. Microsoft says that the data binding limitations are strictly temporary and that future builds of Silverlight 2 will eliminate the problem. Count on future Silverlight releases to add more UI controls, data binding support, and a much needed automated layout manager to the Silverlight mix (see Figure 1-1).

The architecture of Silverlight 1.0 is quite complex (see http://msdn2.microsoft.com/en-us/library/bb404713.aspx for an overview), but it can be broken down into big chunks. The presentation system takes care of everything UI, including animation, text rendering, and audio/video playback. The plug-in itself integrates into the browser so that the content can be shown, as well as accessed using the JavaScript DOM. Finally, using some JavaScript code (or, optimally, the ASP.NET AJAX framework), Silverlight applications can be enriched to access server APIs such as web services. The browser plug-in then parses the markup and runs the code, even if no .NET Framework Redistributable is installed on the client. Silverlight 2 further extends this and offers a partial .NET Framework integration right into Silverlight. So you can write code in languages such as C#; this code will be compiled prior to deployment.

Figure 1-1. Silverlight framework model
 

1.1. Rich Internet Applications
What exactly is a "RIA" web application? And why would you want to adopt the RIA model for your own web development?

Rich Internet Applications, or RIAs, are web applications that have the features and functionality of traditional desktop applications. RIAs typically transfer the processing necessary for the user interface to the web client but keep the bulk of the data processing (such as maintaining the state of the program, the data, etc.) on the application server.

Traditional web applications implement a client/server architecture, in which a thin client (the web browser) interacts with a powerful server. Typically, all processing is done on the server and the client is used only to display static HTML content. The biggest drawback to thin-client implementations is that all interaction with the application must pass through the server. That means data must be sent to the server, the server must respond, and then the page must be reloaded on the client with the server's response. By moving more of this processing to client-side technology that can execute instructions on the client's computer, RIAs can circumvent this slow, synchronous loop for many user interactions.

1.1.1. Benefits of Rich Internet Applications
One of the primary benefits of RIAs is that they can offer user-interface behaviors not possible with only the HTML controls available in standard browser-based web applications. With a RIA platform, web applications are no longer limited by what the browser can do. Rather, they can implement any user interaction that the new RIA platform support, such as drag-and-drop behaviors, smooth animations, and client-side calculations. While some of these interactions are possible without a RIA platform (using Ajax, for example), the RIA approach is typically much more responsive and consistent across platforms.

The benefits of RIAs, however, go beyond their looks. Using a client engine can also produce other performance benefits:

Client-server balance

RIAs shift the balance of computing resources for web applications from the server to the client. This frees up resources on the web server, enabling the same server hardware to handle more concurrent user sessions. On the flip side, the approval it requires that your users have computers that are powerful enough to execute complex client-side code, which is generally not a problem in this day and age.

Asynchronous communication

The RIA client engine can interact with the server asynchronously—that is, without waiting for the user to perform an action such as clicking on a button or link. This feature enables RIA designers to move data between the user's PC and the server without making the user wait for the transfer to finish, similar to what Ajax provides today.

Network efficiency

Network traffic may also be significantly reduced in a RIA because an application-specific client engine can be more intelligent than a standard web browser when deciding what data needs to be exchanged with servers. Transferring less data for each interaction can speed up individual requests and responses, in turn reducing overall network load. Use of asynchronous prefetching techniques, however, can neutralize or even reverse this potential benefit. Because code cannot anticipate exactly what every user will do next, prefetching extra data is common, not all of which is actually needed by many users.

1.1.2. Shortcomings of Rich Internet Applications
While RIAs offer some compelling advantages over current approaches to web development, there are a number of drawbacks that plague the technology—not the least of which are requirements of the browser plug-in itself (in most cases). Among the more serious drawbacks of RIAs are:

Sandbox

Because RIAs run within a sandbox, they have restricted access to system resources. If users modify their systems or have reduced permissions that alter a RIA's ability to access system resources, RIAs may fail to operate correctly.

Disabled scripting

RIAs usually require JavaScript or another scripting language to operate on the client. If the user has disabled active scripting in his browser, the RIA may not function properly, if at all.

Script download time

Although it does not always have to be installed, the additional client-side intelligence (or client engine) of RIA applications needs to be delivered by the server to the client. While much of this is usually automatically cached, it needs to be transferred at least once. Depending on the size and type of delivery, client engine download time may be unpleasantly long, especially for users with slower Internet connections. Some RIA developers can lessen the impact of this delay by compressing scripts and by staging delivery over multiple pages of an application. For client engine s that require a plug-in to be installed, this is not an option.

Loss of visibility to search engines

Search engines may not be able to index the text content of RIA applications. This can be a major problem for web applications that depend on search engine visibility for their success.

Dependence on an Internet connection

While the ideal network-enabled replacement for a desktop application would allow users to be "occasionally connected," wandering in and out of hotspots or from office to office, today (in 2008) the typical RIA requires network connectivity.

我将使用本页链接到有关Silverlight 2的文章和贴子（包括我写的和别人写的），请经常回来查看新的内容，因为我才开始。

入门教程

• Silverlight 2 初览: 我建议先读这个贴子，如果你正考虑开始Silverlight 2开发的话。该文不仅对Silverlight 2提供的功能做了高层次的描述，还链接到了一个八个贴子的系列教程，该教程对如何建造一个Digg客户端例程做了示范。这些教程贴子对Silverlight 2和WPF开发的概念提供了很好的介绍。

• 使用Expression Blend开发Silverlight 2应用 -- 初览: 我建议下载Expression Blend 2.5 三月份预览版，按本教程贴子的步骤进行。我认为它很好地展示了Expression Blend的一些常见功能，用它建造了一个IM聊天客户端例程。

• Unit Testing with Silverlight 2: Silverlight开发团队的Jeff Wilcox有一篇精彩贴子，讨论如何使用Silverlight SDK中的单元测试框架单元测试Silverlight 2应用。

入门讲座

• Building Rich Internet Applications with Silverlight (Part 1 and 2): Joe Stegman和Mike Harsh在MIX 08上做了这分成2个部分的讲座， 讨论如何使用Silverlight建造应用。你可以使用上面的链接观看他们讲座的录像和下载相关讲义和示范例程。

• Creating Rich, Dynamic User Interfaces with Silverlight 2 Controls: Karen Corby在MIX 08上有个极棒的讲座，很好地解释了样式，控件模板，用户控件等等。你可以在这里运行和下载她完整的FlickR应用。

• 我的Silverlight入门讲座: 你可以下载我最近在亚利桑那做的“Silverlight 2入门”讲座的讲义和示范例程，请随意在你自己的讲座中重用这些讲义。

文档链接

• Silverlight 2 QuickStart Tutorials: 这些示范教程在上手Silverlight时会非常有用。

• Silverlight 2 Developer Poster: 下载和打印Silverlight 2开发者海报。

• Silverlight Control Source and Unit Tests: Shawn Burke提供了内置的Silverlight控件的源码以及相关单元测试的链接。

• MSDN Silverlight 2 Beta1 Online Documentation: 这个网页提供了正式的Silverlight 2文档的链接。你可以在这里下载离线版本。

教程和例程

• "How Do I?" with Silverlight: 这个链接连到了含有一堆Silverlight 2录像教程的网页。

• Hard Rock Memorabilia Sample: Vertigo Software公司的Scott Stanfield讨论三月份发布的使用Silverlight 2建造的很酷的Hard Rock Memorabilia网站。

• Using Deep Zoom with Silverlight 2: Jacek Ciereszko有一个很好的博客贴子，描述了如何使用Silverlight 2的 “Deep Zoom”功能实现跟Hard Rock例程类似的图像放大功能。

• Game Programming with Silverlight: Mike Snow正打造一个分成十一个部分的博客系列，讨论如何使用Silverlight开发在线游戏。

• Homepage "Link Cloud" application: Jeff Wilcox讨论他建造的一个很酷的标签云应用。

部署体验

• Providing a Great Silverlight Deployment Experience: Tim Heuer有个很好的贴子，讨论可以为你所用的技术来优化Silverlight安装体验。

• Using Silverlight 2 on a Production Web Server: Brad Abrams有个很好的贴子，讨论在把Silverlight .xap文件拷贝到IIS web服务器时需要注意的几件事情。

控件模板

• Creating a Custom Skin for Silverlight's Button Control: Matt Berseth的一个精彩好贴，讨论Silverlight控件的皮肤和样式功能。

• Writing a Templated Silverlight Control: Shawn Burke有个精彩贴子，详细描述了如何创建定制的Silverlight模板控件。

• Improving Access to Silverlight's Generic.xaml Resources (也阅读 这里的Part 2): David Anson有个很棒的工具，示范如何查看和提取内置Silverlight控件的默认XAML样式。

ListBox和ScrollViewer场景

• Ultimate ListBox and ScrollViewer Frequently Asked Questions Guide: David Anson，Silverlight ListBox和ScrollViewer控件的开发者，编篡了这个很棒的，关于所有这些控件的FAQ以及你可以使用它们的场景。

• Cool (wacky) uses of the ListBox and ScrollViewer controls: David Anson的又一篇精彩贴子，展示了数据和控件模板的灵活性。

DataGrid场景

• Using the Silverlight DataGrid and Defining Columns for a Silverlight DataGrid: Scott Morrison开始了一个精彩贴子系列，描述如何使用新的Silverlight 2 DataGrid控件（他是相关项目的主管，绝对精通！）

• Using Silverlight 2's DataGrid with WCF + LINQ to SQL: 这个15分钟的录像博客示范了如何在服务器上建造一个LINQ to SQL对象模型，然后用WCF将其发布，然后示范了如何建造一个使用了新的Silverlight DataGrid控件的Silverlight客户端，该客户端调用WCF服务获取LINQ to SQL数据，将其绑定到DataGrid上。

• Simple Editing of Web Service Data in a DataGrid: Mike Taulty有一篇好贴，展示如何在服务器上建造WCF服务，然后从Silverlight 2客户端使用它来获取数据，绑定到DataGrid，允许用户更新数据行，添加/删除数据行，然后使用 Silverlight 2 Beta1将数据保存到服务器上。

• Sorting with Silverlight 2's DataGrid Control: Silverlight 2 Beta1中的DataGrid控件还没有内置的列数据排序支持（将在Beta2中提供），但这并没有阻止Matt Berseth！ 在这个贴子里，他展示了如何使用一个定制的header列方法来实现排序。也看一下Matt的 这里的贴子，该文提供了一个DataGrid测试页面，展示了目前DataGrid的若干特性。

Web Services 和 Networking

• Web Services and Silverlight: 这个有用的贴子讨论了如何在Silverlight中使用web服务，并且提供了相关快速入门例程和文档的链接。

• Calling Web Services with Silverlight 2 (Part 1) and (Part 2): Tim Heuer的几篇精彩贴子，讨论如何使用Silverlight调用web服务。

Video场景

• Encoding Video for Microsoft Silverlight Delivery: Ben Waggoner在MIX 08上的讲座，讨论编码Silverlight录像的最佳实践。

Accessibility 和 508相容性

• Accessibility in Silverlight 2: Silverlight开发团队的Mark Rideout讨论 Silverlight 2 中的accessibility支持，以及如何使用Silverlight建造与section 508相容的accessible方案。

希望本文对你有所帮助，

Scott