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Working with Layouts

Rails uses layouts to interpolate the output of an individual template into a larger whole—a reversal of
the common pattern of including a shared header and footer on every page (which, if you’ve done any
work in languages like PHP and ASP, is all too familiar). The scaffold generator you ran in Chapter 3
created a layout file and placed it in app/views/layouts/application.html.erb. The application.html.erb
layout is applied to all controllers. However, if you like your layout to apply to a specific controller, you
can create a layout file named after the controller you want. For example, a layout that applies only to
the articles controller should be created in app/views/layouts/articles.html.erb. That’s the way it works
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CHAPTER 6
ACTION PACK: WORKING WITH THE VIEW AND THE CONTROLLER
in Rails. Just as an action tries to render itself using a view that matches its name, a controller attempts
to use a layout that matches its name.
Open the app/views/layouts/application.html.erb in your editor. You should see something like

the file shown in Listing 6-6.
Listing 6-6. The app/views/layouts/application.html.erb File
<!DOCTYPE html>
<html>
<head>
<title>Blog</title>
<%= stylesheet_link_tag :all %>
<%= javascript_include_tag :defaults %>
<%= csrf_meta_tag %>
</head>
<body>
<%= yield %>
</body>
</html>
At rendering time, the layout yields the results of the template fragment’s execution in place. See the
<%= yield %> bit that’s highlighted in bold? That’s the important part. Wherever you put the yield
keyword is where your content goes.
One more thing to note: Rails is all about convention over configuration. Here, the convention is
that a layout with the name application.html.erb is automatically applied to all templates unless an
alternate is specified. This means that if you change the name of the layout as it stands, it won’t be
automatically applied. If you want to apply a different layout to a given controller, you can either have a
layout named after the controller or specify it in the controller using the class method layout:
class ExampleController < ApplicationController
layout 'my_layout' # Will use a layout in app/views/layouts/my_layout.html.erb
end