n the first article in this series, I discussed how to create Windows Presentation Foundation (WPF; code named Avalon) applications using XAML. In a follow-up article, I discussed the new navigational model in WPF. In this third installment, I will explore another important concept in WPF programming?data binding.

In WPF you can bind UI elements to a wide variety of data sources, including XML data, Web services, as well as databases. Data binding is a big topic in WPF and it is beyond the scope of this article to discuss every nook and cranny of data binding. To keep things manageable, I will show you how you can data bind a typical WPF application to an XML data source and explain the nuts and bolts behind it. To make the example useful, I will build a simple RSS reader that accepts an RSS XML document and displays the various items in the document using data binding. Figure 1 shows the completed application.

Binding to a Static XML Source
To build the sample application in this article, you need Visual Studio 2005 Beta 2 with the WinFX SDK installed. Using Visual Studio 2005 Beta 2, create a new AvalonNavigation application (see Figure 2). Name the application DataBinding and click OK.

Figure 1. The Avalon RSS Reader Application: In this example, the DevX New Articles RSS feed is used to generate the data for the sample application.

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Figure 2. Creating a New AvalonNavigation Application: Start your project in Visual Studio in the usual way, choosing the AvalonNavigation type.

In the default Page1.xaml, you will first build the UI of the application by populating the page with the relevant XAML elements.

First, add a element to the page and set its background color to “Cornsilk”:

Add a element to the page (see Listing 1). The element allows you to define an XML Data source (also known as XML data island) to be used for this application. In this case, the XML source is an RSS document. The XPath attribute is set to “/rss/channel” as the starting node of the document tree so that later on you can simply refer to the child elements using relative paths. The XML data source is given the key RSSData. The code is shown in Listing 1.

Next, add a element to the element. The element is used to bind the content of the XML data island with a control (in this case the TextBlock control). The TextBlock data template is bound to the