How Can I Implement Conditional CSS Rendering in Rails 3.1?

Conditional CSS Rendering in Rails 3.1

The Rails 3.1 asset pipeline offers a powerful mechanism for managing static assets, including CSS files. However, rendering CSS conditionally based on specific criteria can be a challenging task.

The Default Approach

By default, the *= require_tree command includes all CSS files within the assets/stylesheets directory. This approach can lead to a large and unreadable CSS bundle.

Individual File Inclusion

As a workaround, you can manually specify each CSS file individually in your application.css manifest. While this method provides finer control, it can be tedious and inflexible.

A Smarter Solution

A more elegant solution involves using separate manifest files to break down CSS requirements into logical groups. This approach allows you to automatically add new stylesheets without the need for manual editing.

Step 1: Reorganize Asset Structure

Start by reorganizing your app/assets/stylesheets folder into the following structure:

• all: Contains your base stylesheet and any stylesheets that apply to all views.
• print: Contains stylesheets specific to printing.
• ie: Contains stylesheets specific to Internet Explorer browsers.
• application-all.css: A manifest file that includes all CSS files within the "all" directory.
• application-print.css: A manifest file that includes all CSS files within the "print" directory.
• application-ie.css: A manifest file that includes all CSS files within the "ie" directory.

Step 2: Edit Manifest Files

Next, edit the three manifest files as shown below:

# application-all.css
*= require_self
*= require_tree ./all

# application-print.css
*= require_self
*= require_tree ./print

# application-ie.css
*= require_self
*= require_tree ./ie

Step 3: Update Application Layout

Modify your application layout to include the new manifest files:

<%= stylesheet_link_tag "application-all", :media => "all" %>
<%= stylesheet_link_tag "application-print", :media => "print" %>

<!--[if lte IE 8]>
    <%= stylesheet_link_tag "application-ie", :media => "all" %>
<![endif]-->

Step 4: Configure Production Environment

Add the new manifest files to your config/environments/production.rb:

config.assets.precompile += %w( application-all.css application-print.css application-ie.css )

Note on Image References

Be aware that this conditional rendering approach may affect image references within your stylesheets. To ensure proper image loading, you can move images to follow the same folder structure, qualify image paths, or use the SASS helper image-url('image.png').

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