An Arbitrary Cycle Method For ASP.NET MVC

asp.net, asp.net mvc comments edit

In his Practical Review of ASP.NET MVC, Josh Charles provides a helpful review of ASP.NET MVC from a Rails developer’s perspective. It seemed fair and balanced, and the end result is that there’s room for improvement, which we’re taking to heart.

However, that’s not the part that caught my attention. He mentioned that he wrote a cycle method but couldn’t write it as an extension method to HtmlHelper.

this was an instance method that would take two strings and return the one that it didn’t return the last time it was called. In my templates, I used this to change the classes for each row of data, to give them different background colors. I considered writing an extension method to the Html object used for other Html operations in the view page, but this method specifically required the use of an additional private variable, so that would not work.

If you don’t mind cheating a bit, there is a way to write this as an extension method. And while we’re doing that, why stop at only two strings? Why not take an indefinite number? :)

public static string Cycle(this HtmlHelper html, params string[] strings) {
    var context = html.ViewContext.HttpContext;
    int index = Convert.ToInt32(context.Items["cycle_index"]);

    string returnValue = strings[index % strings.Length];

    html.ViewContext.HttpContext.Items["cycle_index"] = ++index;
    return returnValue;
}

Perhaps allowing an indefinite number of strings is overkill (who ever heard of a table with tri-color highlighting?) but I thought it was fun to do regardless. Here’s an example of usage with three different CSS styles:

<style>
    .first {background-color: #ddd;}
    .second {background-color: khaki;}
    .third {background-color: #fdd;}
</style>

<table>
<% for (int i = 0; i < 5; i++) { %>
    <tr class="<%= Html.Cycle("first", "second", "third") %>">
        <td>Stuff</td>
    </tr>
<% } %>
</table>

And the output...

<table><tbody>
    <tr class="first">
      <td>Stuff</td>
    </tr>

    <tr class="second">
      <td>Stuff</td>
    </tr>

    <tr class="third">
      <td>Stuff</td>
    </tr>

    <tr class="first">
      <td>Stuff</td>
    </tr>

    <tr class="second">
      <td>Stuff</td>
    </tr>
  </tbody></table>

With this, go forth and spread tri-color highlighted tables all over the web. Or if you’re really crazy player, go with four color highlighting!

Technorati Tags: aspnetmvc,helpers,review

Comments