Mike-Ward.Net

ASP.NET Data Binding Expression Syntax Tip

Bloget™ uses ASP.NET’s built in template syntax for customization (other ASP.NET templated server controls include Repeater and GridView). It’s one of those killer ASP.NET features (IMHO) that doesn’t get enough press. Coupled with data binding, it makes for a formidable template system that I use to develop Bloget blogs. Recently however, I stumbled trying to do something seemingly simple. First, however, let’s quickly review the Data Binding Syntax in ASP.NET

<asp:Hyperlink NavigateUrl='<%# Container.ItemPermaLink %>'  
  runat="server">permalink</asp:HyperLink>

This is an example from a Bloget template I’m developing. The <%# %> contains a data binding expression. The Container is the naming container that Bloget is hosted in and is the standard way to access data bound objects in a template. When the template is realized, Container.ItemPermaLink will expand to the actual permalink for the item. So far so simple.

Where I stumbled was when I wanted to build a custom link to Digg, a popular bookmarking site. The format of the URL to submit a link is as follows:

http://digg.com/submit?phase=2&url=<link>&title=<title>

The <link> and <title> portions are replaced by the link and title of the blog article at run time. The documentation for Data Binding Expressions and every example I could find suggest that only a data binding expression can be contained in the <%# %> portion. Well I’m here to say it ain’t so! You can actually use C# (or VB) in these expressions. It may be common knowledge, but if it is, I couldn’t find it. Armed with this new knowledge, it becomes straightforward to build the link.

<asp:HyperLink NavigateURL='<%# string.Format(  
  "http://digg.com/submit?phase=2&amp;url={0}&amp;title={1}",  
  Container.ItemPermaLink, Container.ItemTitleUrlEncoded) %>'  
  runat="server">Digg this!</asp:HyperLink>

This works fine in ASP.NET 2.0. I don’t use ASP.NET 1.1 so your mileage may vary.

Technorati tags: ASP.NET, C#, Bloget