module ActionController #:nodoc: module Layout #:nodoc: def self.included(base) base.extend(ClassMethods) base.class_eval do class << self alias_method_chain :inherited, :layout end end 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 # 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) write_inheritable_attribute(:layout, template_name) write_inheritable_attribute(:auto_layout, auto) end def layout_conditions #:nodoc: @layout_conditions ||= read_inheritable_attribute(:layout_conditions) end def default_layout(format) #:nodoc: layout = read_inheritable_attribute(:layout) return layout unless read_inheritable_attribute(:auto_layout) find_layout(layout, format) end def find_layout(layout, *formats) #:nodoc: return layout if layout.respond_to?(:render) view_paths.find_template(layout.to_s =~ /layouts\// ? layout : "layouts/#{layout}", *formats) end private def inherited_with_layout(child) inherited_without_layout(child) unless child.name.blank? layout_match = child.name.underscore.sub(/_controller$/, '').sub(/^controllers\//, '') child.layout(layout_match, {}, true) if child.find_layout(layout_match, :all) end end def add_layout_conditions(conditions) write_inheritable_hash(:layout_conditions, normalize_conditions(conditions)) end def normalize_conditions(conditions) conditions.inject({}) {|hash, (key, value)| hash.merge(key => [value].flatten.map {|action| action.to_s})} end end # Returns the name of the active layout. If the layout was specified as a method reference (through a symbol), this method # is called and the return value is used. Likewise if the layout was specified as an inline method (through a proc or method # object). If the layout was defined without a directory, layouts is assumed. So layout "weblog/standard" will return # weblog/standard, but layout "standard" will return layouts/standard. def active_layout(passed_layout = nil) layout = passed_layout || self.class.default_layout(default_template_format) active_layout = case layout when Symbol then __send__(layout) when Proc then layout.call(self) else layout end if active_layout if layout = self.class.find_layout(active_layout, @template.template_format) layout else raise ActionView::MissingTemplate.new(self.class.view_paths, active_layout) end end end private def candidate_for_layout?(options) options.values_at(:text, :xml, :json, :file, :inline, :partial, :nothing, :update).compact.empty? && !@template.__send__(:_exempt_from_layout?, options[:template] || default_template_name(options[:action])) end def pick_layout(options) if options.has_key?(:layout) case layout = options.delete(:layout) when FalseClass nil when NilClass, TrueClass active_layout if action_has_layout? && !@template.__send__(:_exempt_from_layout?, default_template_name) else active_layout(layout) end else active_layout if action_has_layout? && candidate_for_layout?(options) end end def action_has_layout? if conditions = self.class.layout_conditions case when only = conditions[:only] only.include?(action_name) when except = conditions[:except] !except.include?(action_name) else true end else true end end def default_template_format response.template.template_format end end end