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Using an extension method to strongly type your navigation

, 14 Apr 2009 CPOL
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After writing a very large web-based application with lots of pages, I realized that I was falling into a trap.

Magic strings were going to be the death of me!

If you are not familiar with what a "magic string" is, it is really any type of string in your application that is not strongly typed somehow. For example, if you write a paragraph like this:

...
lblParagraph.Text = "<p>This is a paragraph."; 
...

you have a lot of string magic going on! You probably would want to refactor that to have a strongly typed object that implies you are dealing with a paragraph, and then refer to the text based on its source, whether it's a constant, resource, or another way to inject the information without making it magically reside in the code.

So, what is a common pattern in our website (this is addressed in MVC, by the way, I'm talking the old WebForms engine)?

...
Response.Redirect("~/Some/Page.aspx"); 
...

This seems fine until you end up refactoring the page or splitting it up, etc. Isn't there a better way?

My first step was to start to use constants like this:

const string NAVIGATE_SOME_PAGE = "~/Some/Page.aspx"; 
...
Response.Redirect(NAVIGATE_SOME_PAGE); 

This was a little more satisfying, until I realized that I was dotting my entire application with multiple "NAVIGATE_SOME_PAGE" references. I could have hacked it by referencing them publicly, but was that really the right way?

Fortunately, our application follows strict naming conventions including adhering to proper namespace use. We don't create a folder called "foo" and then stick an entity in that folder into the namespace "bar".

So, I decided to come up with an extension method. Why an extension method? Because, I couldn't think of some dummy utility class to paste then on when it really is a function of the "Page" knowing where "it" is. So, I extended the page, and did this:

/// <span class="code-SummaryComment"><summary>
</span>/// Contains extension methods for System.Web.UI.Page
/// <span class="code-SummaryComment"></summary>
</span>public static class PageExtensions
{
   /// <span class="code-SummaryComment"><summary>
</span>   ///     Gets the redirect url based on type
   /// <span class="code-SummaryComment"></summary>
</span>   /// <span class="code-SummaryComment"><typeparam name="T">The type of the page</typeparam>
</span>   /// <span class="code-SummaryComment"><returns>The path to the page</returns>
</span>   public static string GetRedirect<T>(this System.Web.UI.Page page) 
                        where T : BaseController
   {
       const string ROOT_NAMESPACE = "MyNamespace.Web";

       string str = typeof(T).FullName;

       // remove the prefix 
       str = str.Replace(ROOT_NAMESPACE, "~");

       // build the path
       str = str.Replace(".", "/");

       // append the suffix 
       str += ".aspx";

       return str;
    }
}

Note: this implies you inherit your pages from BaseController .. you could just as easily make it System.Web.UI.Page.

Now, when I want to redirect, I do this:

...
Response.Redirect(Page.GetRedirect<Some.Page>());
...

And, the best part? If I delete the page, my compiler throws errors. If I refactor the page, all of the redirects will get refactored with it.

(I realize hacking the namespace to make a path doesn't seem the most elegant solution, but it's the best I could come up with ... I'm very open to other ideas on how to tackle this).

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Jeremy Likness
Architect Wintellect
United States United States
Jeremy Likness is a principal consultant at Wintellect. Jeremy, an experienced entrepreneur and technology executive, has successfully helped ship commercial enterprise software for 20 years. He specializes in catalyzing growth, developing ideas and creating value through delivering software in technical enterprises. His roles as business owner, technology executive and hands-on developer provided unique opportunities to directly impact the bottom line of multiple businesses by helping them grow and increase their organizational capacity while improving operational efficiency. He has worked with several initially small companies like Manhattan Associates and AirWatch before they grew large and experienced their transition from good to great while helping direct vision and strategy to embrace changing technology and markets. Jeremy is capable of quickly adapting to new paradigms and helps technology teams endure change by providing strong leadership, working with team members “in the trenches” and mentoring them in the soft skills that are key for engineers to bridge the gap between business and technology.
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Comments and Discussions

 
GeneralMy vote of 5 Pinmemberzenwalker198528-Jun-11 18:40 
AnswerAn alternative way to do this that also gives you strongly typed page parameters PinmemberHightechRider14-Apr-09 17:36 

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