conditional formatting in rails partials

Question

I am rendering a rails partial and I want to alternate the background color when it renders the partial. I know that is not super clear so here is an example of what I want to do:

Row One grey Background Row Two yellow background Row Three grey Background Row Four yellow background

• sorry stackoverflow seams to prevent the background colors from being shown but I think this makes my idea clear

This is the view code that I am using

<table>
  <%= render :partial => 'row' :collection => @rows %>
</table>

the _row.html.erb partial looks like this

<tr bgcolor="#AAAAAA">
  <td><%= row.name %></td>
</tr>

The problem is I do not know how to change the background color for every other row. Is there a way to do this?

Answer 1

You could use the Cycle helper. Something like this:

<tr class="<%= cycle("even", "odd") %>">
  <td><%= row.name %></td>
</tr>

Or in your case use bgcolor instead, although i would recomend using css classes.

You can cycle through more than two values: cycle(‘first’, ‘second’, ‘third’, ‘and_more’).

There is also: reset_cycle(‘cycle_name’) This makes sure that on each iteration, you will start again with your first value of the cycle list.

Check the rails documentation for more examples.

Answer 2

Another idea, you can use javascript to change the element's style based on (total number of TD's % 2).

That way all your visual stuff are contained in html/css/javascript layer. Then again, this technique does not work if javascript is disabled.

Answer 3

There is one "gotcha" with cycle: If you should append to the string, the cycle breaks. For example,

cycle('odd', 'even') << " some other classes"

will break the cycle. However, reversing the order or constructing a string works fine:

"some other classes " << cycle('odd', 'even')
"#{cycle('odd', 'even')} some other classes"

I've not (yet) delved into the source to see why this may be so. Also, I'm using Rails 3.2.x