module ActionController # Layouts reverse the common pattern of including shared headers and footers in many templates to isolate changes in # repeated setups. The inclusion pattern has pages that look like this: # # <%= render "shared/header" %> # Hello World # <%= render "shared/footer" %> # # This approach is a decent way of keeping common structures isolated from the changing content, but it's verbose # and if you ever want to change the structure of these two includes, you'll have to change all the templates. # # With layouts, you can flip it around and have the common structure know where to insert changing content. This means # that the header and footer are only mentioned in one place, like this: # # // The header part of this layout # <%= yield %> # // The footer part of this layout # # And then you have content pages that look like this: # # hello world # # At rendering time, the content page is computed and then inserted in the layout, like this: # # // The header part of this layout # hello world # // The footer part of this layout # # == Accessing shared variables # # Layouts have access to variables specified in the content pages and vice versa. This allows you to have layouts with # references that won't materialize before rendering time: # #

<%= @page_title %>

# <%= yield %> # # ...and content pages that fulfill these references _at_ rendering time: # # <% @page_title = "Welcome" %> # Off-world colonies offers you a chance to start a new life # # The result after rendering is: # #

Welcome

# Off-world colonies offers you a chance to start a new life # # == Layout assignment # # You can either specify a layout declaratively (using the #layout class method) or give # it the same name as your controller, and place it in app/views/layouts. # If a subclass does not have a layout specified, it inherits its layout using normal Ruby inheritance. # # For instance, if you have PostsController and a template named app/views/layouts/posts.html.erb, # that template will be used for all actions in PostsController and controllers inheriting # from PostsController. # # If you use a module, for instance Weblog::PostsController, you will need a template named # app/views/layouts/weblog/posts.html.erb. # # Since all your controllers inherit from ApplicationController, they will use # app/views/layouts/application.html.erb if no other layout is specified # or provided. # # == Inheritance Examples # # class BankController < ActionController::Base # layout "bank_standard" # # class InformationController < BankController # # class TellerController < BankController # # teller.html.erb exists # # class TillController < TellerController # # class VaultController < BankController # layout :access_level_layout # # class EmployeeController < BankController # layout nil # # The InformationController uses "bank_standard" inherited from the BankController, the VaultController overwrites # and picks the layout dynamically, and the EmployeeController doesn't want to use a layout at all. # # The TellerController uses +teller.html.erb+, and TillController inherits that layout and # uses it as well. # # == Types of layouts # # Layouts are basically just regular templates, but the name of this template needs not be specified statically. Sometimes # you want to alternate layouts depending on runtime information, such as whether someone is logged in or not. This can # be done either by specifying a method reference as a symbol or using an inline method (as a proc). # # The method reference is the preferred approach to variable layouts and is used like this: # # class WeblogController < ActionController::Base # layout :writers_and_readers # # def index # # fetching posts # end # # private # def writers_and_readers # logged_in? ? "writer_layout" : "reader_layout" # end # # Now when a new request for the index action is processed, the layout will vary depending on whether the person accessing # is logged in or not. # # If you want to use an inline method, such as a proc, do something like this: # # class WeblogController < ActionController::Base # layout proc{ |controller| controller.logged_in? ? "writer_layout" : "reader_layout" } # # Of course, the most common way of specifying a layout is still just as a plain template name: # # class WeblogController < ActionController::Base # layout "weblog_standard" # # If no directory is specified for the template name, the template will by default be looked for in app/views/layouts/. # Otherwise, it will be looked up relative to the template root. # # == Conditional layouts # # If you have a layout that by default is applied to all the actions of a controller, you still have the option of rendering # a given action or set of actions without a layout, or restricting a layout to only a single action or a set of actions. The # :only and :except options can be passed to the layout call. For example: # # class WeblogController < ActionController::Base # layout "weblog_standard", :except => :rss # # # ... # # end # # This will assign "weblog_standard" as the WeblogController's layout except for the +rss+ action, which will not wrap a layout # around the rendered view. # # Both the :only and :except condition can accept an arbitrary number of method references, so # #:except => [ :rss, :text_only ] is valid, as is :except => :rss. # # == Using a different layout in the action render call # # If most of your actions use the same layout, it makes perfect sense to define a controller-wide layout as described above. # Sometimes you'll have exceptions where one action wants to use a different layout than the rest of the controller. # You can do this by passing a :layout option to the render call. For example: # # class WeblogController < ActionController::Base # layout "weblog_standard" # # def help # render :action => "help", :layout => "help" # end # end # # This will render the help action with the "help" layout instead of the controller-wide "weblog_standard" layout. module Layouts extend ActiveSupport::Concern include ActionController::Renderer include AbstractController::Layouts module ClassMethods # If no layout is provided, look for a layout with this name. def _implied_layout_name controller_path end end private def _determine_template(options) super return if (options.key?(:text) || options.key?(:inline) || options.key?(:partial)) && !options.key?(:layout) layout = options.key?(:layout) ? options[:layout] : :default options[:_layout] = _layout_for_option(layout, options[:_template].details) end def _layout_for_option(name, details) case name when String then _layout_for_name(name, details) when true then _default_layout(details, true) when :default then _default_layout(details, false) when false, nil then nil else raise ArgumentError, "String, true, or false, expected for `layout'; you passed #{name.inspect}" end end end end