module ActionController #:nodoc: module Layout #:nodoc: def self.included(base) base.extend(ClassMethods) base.class_inheritable_accessor :layout_name, :layout_conditions end # 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 # # NOTE: The old notation for rendering the view from a layout was to expose the magic @content_for_layout instance # variable. The preferred notation now is to use yield, as documented above. # # == 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 # # == Automatic layout assignment # # If there is a template in app/views/layouts/ with the same name as the current controller then it will be automatically # set as that controller's layout unless explicitly told otherwise. Say you have a WeblogController, for example. If a template named # app/views/layouts/weblog.erb or app/views/layouts/weblog.builder exists then it will be automatically set as # the layout for your WeblogController. You can create a layout with the name application.erb or application.builder # and this will be set as the default controller if there is no layout with the same name as the current controller and there is # no layout explicitly assigned with the +layout+ method. Nested controllers use the same folder structure for automatic layout. # assignment. So an Admin::WeblogController will look for a template named app/views/layouts/admin/weblog.erb. # Setting a layout explicitly will always override the automatic behaviour for the controller where the layout is set. # Explicitly setting the layout in a parent class, though, will not override the child class's layout assignment if the child # class has a layout with the same name. # # == Inheritance for layouts # # Layouts are shared downwards in the inheritance hierarchy, but not upwards. Examples: # # class BankController < ActionController::Base # layout "bank_standard" # # class InformationController < BankController # # 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. # # == 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 ClassMethods extend ActiveSupport::Memoizable # If a layout is specified, all rendered actions will have their result rendered # when the layout yields. This layout can itself depend on instance variables assigned during action # performance and have access to them as any normal template would. def layout(template_name, conditions = {}, auto = false) add_layout_conditions(conditions) self.layout_name = template_name end def memoized_default_layout(formats) #:nodoc: self.layout_name || begin layout = default_layout_name layout.is_a?(String) ? find_layout(layout, formats) : layout rescue ActionView::MissingTemplate end end def default_layout(*args) (@_memoized_default_layout ||= ::ActiveSupport::ConcurrentHash.new)[args] ||= memoized_default_layout(*args) end def memoized_find_layout(layout, formats) #:nodoc: return layout if layout.nil? || layout.respond_to?(:render) prefix = layout.to_s =~ /layouts\// ? nil : "layouts" view_paths.find_by_parts(layout.to_s, formats, prefix) end def find_layout(*args) (@_memoized_find_layout ||= ::ActiveSupport::ConcurrentHash.new)[args] ||= memoized_find_layout(*args) end def layout_list #:nodoc: Array(view_paths).sum([]) { |path| Dir["#{path.to_str}/layouts/**/*"] } end memoize :layout_list def default_layout_name layout_match = name.underscore.sub(/_controller$/, '') if layout_list.grep(%r{layouts/#{layout_match}(\.[a-z][0-9a-z]*)+$}).empty? superclass.default_layout_name if superclass.respond_to?(:default_layout_name) else layout_match end end memoize :default_layout_name private def add_layout_conditions(conditions) # :except => :foo == :except => [:foo] == :except => "foo" == :except => ["foo"] conditions.each {|k, v| conditions[k] = Array(v).map {|a| a.to_s} } write_inheritable_hash(:layout_conditions, conditions) end end def active_layout(name) name = self.class.default_layout(formats) if name == true layout_name = case name when Symbol then __send__(name) when Proc then name.call(self) else name end self.class.find_layout(layout_name, formats) end def _pick_layout(layout_name, implicit = false) return unless layout_name || implicit layout_name = true if layout_name.nil? active_layout(layout_name) if action_has_layout? && layout_name end private def action_has_layout? if conditions = self.class.layout_conditions if only = conditions[:only] return only.include?(action_name) elsif except = conditions[:except] return !except.include?(action_name) end end true end end end