MSDN Magazine - April 2008 - (Page 36)

A reasonable method for populating a MenuItem collection is to render information from an XML file. Here’s a possible schema for the document: Something : Figure 2 Nested ListViews <asp:ListView runat=”server” ID=”subMenu” ItemPlaceholderID=”PlaceHolder3” DataSource=’ ’> <a href=’ ’> The following demonstrates how to use LINQ to XML to load and process the content: var doc = XDocument.Load(Server.MapPath(“dataMap.xml”)); var menu = (from e in doc.Descendants(“RightMenuItems”) select e).First(); var menuLinks = from mi in menu.Descendants(“MenuItem”) select new { Title = mi.Value, Links = ( ) }; After loading the document, you select the first node named RightMenuItems and then grab all of its MenuItem children. The content of each MenuItem node is loaded into a new anonymous type with two properties—Title and Links. How would you populate the Links collection? Here’s some code: Links = (from l in mi.Descendants(“Link”) select new {Url=l.Attribute(“url”).Value, Text=l.Attribute(“text”).Value}) The next step is to bind this compound data to the user interface. As mentioned, you use an outer ListView to render the title and a second, nested ListView to render the list of child links (see Figure 2). Note that the innermost ListView must be bound to data using the Eval method—any other approach will not work: <asp:ListView runat=”server” ID=”subMenu” ItemPlaceholderID=”PlaceHolder3” DataSource=’ ’> You start the data binding process by attaching data to the toplevel ListView. When this happens, the body of the ListView is rendered entirely, including the nested ListView. You could, in theory, intercept the ItemDataBound event of the parent ListView, walk your way through the control tree, grab a reference to the child ListView, and bind it programmatically to data. If you do, you won’t throw an exception, but the binding command on the inner ListView is lost because it fires too late to affect the rendering. A databinding expression, on the other hand, is automatically evaluated during any data-binding event at just the right point in the control lifecycle. This ensures that the correct data is bound properly to the user interface. Building a Hierarchical View The same model for populating a hierarchical menu can be employed for building any hierarchical view of data. In this case, an alternate option would be to use a TreeView control to prepare a multi-level representation of the data. Data binding on a TreeView control, though, requires a hierarchical data source. Using nested ListView controls gives you more flexibility with regard to both the structure of the data source and the resulting user interface. Let’s expand on these concepts. Suppose you need to create a hierarchical grid of data where customers, orders, and order details are displayed according to existing table relationships. How would you retrieve the data and bind 36 msdnmagazine Cutting Edge http://www.silverlight-tour.com http://www.silverlight-tour.com

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

MSDN Magazine - April 2008 Contents Toolbox CLR Inside Out Basic Instincts Cutting Edge Foundations Test Run Service Station Windows with C++ Going Places { End Bracket }

MSDN Magazine - April 2008

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