New XML Features in .NET Version 2: Part III

asp:Feature

LANGUAGES: C#

ASP.NET VERSIONS: 2.0

 

New XML Features in .NET Version 2: Part III

XML Data Binding

 

By Dan Wahlin

 

Version 2 of the .NET Framework provides several new enhancements that make it easier than ever for developers to parse, validate, transform, and bind XML data. Part I of this series demonstrated how to parse XML using new methods found in the XmlReader class and how XML data can be generated using the XmlWriter class. Part II focused on editing XML loaded into memory and validating it using the XmlDocument and XPathNavigator classes. Part II also showed how to perform more efficient XSLT transformations using the new XslCompiledTransform class.

 

In this final article in the series you ll be introduced to several new controls available in ASP.NET 2.0 that simplify working with XML. You ll see how to use the XmlDataSource data source control to bind data to different ASP.NET server controls and be introduced to the TreeView control. Before moving ahead to the new XML features found in version 2, it s worthwhile to take a quick look at how XML data binding occurred in .NET 1.1.

 

XML Data Binding in .NET 1.1

The simplest way to bind XML to server controls in .NET 1.1 was to load an XML document into an XmlDataDocument class and then convert it to a DataSet or simply load a document directly into a DataSet using the ReadXml method. An example of using ReadXml to bind RSS data to a DataList control named dlRss is shown in Figure 1.

 

DataSet ds = new DataSet();

ds.ReadXml("http://msdn.microsoft.com/rss.xml");

//RSS items will be placed into the 3rd DataTable

dlRss.DataSource = ds.Tables[2].DefaultView;

dlRss.DataBind();

Figure 1: Loading XML data into a DataSet using the ReadXml method.

 

If you re new to RSS, Figure 2 shows a simple example of an RSS 2.0 document. Notice that details about an article are marked up using an element. RSS items can have several different child elements that describe an item, such as title, link, pubDate, and creator.

 

 

   

   http://www.xmlforasp.net/XML/RssGenerator.aspx/

   RSS Channel description.

   en-us

   Mon, 23 Jan 2006 14:04:35 GMT

   Mon, 23 Jan 2006 14:04:35 GMT

   XML for ASP.NET Generator

   1440

   

     

     asp.netPRO Magazine Article

     Dan Wahlin

     Sat, 21 Jan 2006 18:00:00 GMT

   

   

 

Figure 2: RSS documents allow different types of items to be marked up using elements. Although RSS documents are often used to mark up articles, they can be used for many other types of things, including product information, software patches, and more.

 

Once an RSS document such as the one shown in Figure 2 is loaded into a DataSet, the appropriate columns in the DataTable must be bound to the target server control. An example of creating a DataList control ItemTemplate that binds to link and title columns is shown here:

 

 

   <%# DataBinder.Eval(Container.DataItem,"title") %>

 

 

Although this approach doesn t require a lot of code, it does requires you to think of the XML data in a relational manner (rows and columns) rather than hierarchically. It also makes locating the data you want from the original RSS document a little tricky because you need to know which DataTable contains the RSS tags that you want to bind to the DataList. This is because of how the DataSet loads XML data. Each level of nesting found in an XML document causes a new DataTable to be created in the DataSet. The tags in an RSS document are automatically loaded into DataTable #3 because these tags are nested three levels deep in the XML hierarchy.

 

If the RSS data being bound to the DataList control needs to be filtered, you ll need to use the DataView class RowFilter property rather than filtering with a simple XPath expression. An example of filtering out RSS items that don t have the word XML in the title is shown in Figure 3.

 

DataSet ds = new DataSet();

ds.ReadXml("http://msdn.microsoft.com/rss.xml");

DataView view = ds.Tables[2].DefaultView;

view.RowFilter = "title LIKE '%XML%'";

DataList1.DataSource = view;

DataList1.DataBind();

Figure 3: Filtering XML data using the DataView class RowFilter property.

 

This type of code certainly works and is fairly simple to write but it doesn t allow you to leverage XML technologies to their full extent and requires more code than should really be necessary for such a simple task. Let s look at how to eliminate this code completely using new classes available in version 2 of the .NET Framework.

 

Using the XmlDataSource Control

ASP.NET version 2 contains several data source controls that are designed to interact with different types of data sources without writing VB.NET or C# code. Data source controls included in .NET version 2 include SqlDataSource, ObjectDataSource, AccessDataSource, XmlDataSource, and SiteMapDataSource. The XmlDataSource control derives from a new class named HierarchicalDataSourceControl and can be used to bind XML documents to different ASP.NET server controls, such as the DataList, TreeView, and Menu controls. It can also be used to bind data to controls normally used with relational data, such as the GridView and DataList controls.

 

Adding an XmlDataSource control to an ASP.NET Web Form is done by using the tag (see Figure 4). In addition to adding the standard ID and Runat attributes, the control also allows you to define the XML document source using the DataFile property. You can also define what nodes contain the actual data that you want to bind by using the XPath property. The XPath property value shown in Figure 4 instructs the XmlDataSource control to start at the root element, move down to the child element, and then select all elements under (refer to Figure 2 to see how these elements are nested).

 

 DataSourceID="RSSDataSource">

   ...DataList templates

 DataFile="http://msdn.microsoft.com/rss.xml"

 XPath="rss/channel/item"

/>

Figure 4: Binding an XmlDataSource data source control to a DataList control.

 

Binding data contained within the XmlDataSource control can be done by using the DataList s new DataSourceID property, as shown in Figure 4. At run time, the DataList will locate the XmlDataSource control based on its ID, and automatically bind the data.

 

You may be wondering how the DataList knows what data to output as it binds to the XmlDataSource control. The XmlDataSource s XPath property identifies which nodes to bind ( nodes in this example), but RSS nodes can have several different children such as