module ActionController #:nodoc: module Layout #:nodoc: def self.included(base) base.extend(ClassMethods) base.class_eval do # NOTE: Can't use alias_method_chain here because +render_without_layout+ is already # defined as a publicly exposed method alias_method :render_with_no_layout, :render alias_method :render, :render_with_a_layout 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 # # Not a word about common structures. 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 # # == 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 assignement 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 by looked for in +app/views/layouts/+. # # == 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. # Some times you'll have exceptions, though, where one action wants to use a different layout than the rest of the controller. # This is possible using the render method. It's just a bit more manual work as you'll have to supply fully # qualified template and layout names as this example shows: # # class WeblogController < ActionController::Base # def help # render :action => "help/index", :layout => "help" # end # end # # As you can see, you pass the template as the first parameter, the status code as the second ("200" is OK), and the layout # as the third. # # 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. module ClassMethods # If a layout is specified, all rendered actions will have their result rendered # when the layoutyield's. 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 = {}) add_layout_conditions(conditions) write_inheritable_attribute "layout", template_name end def layout_conditions #:nodoc: @layout_conditions ||= read_inheritable_attribute("layout_conditions") end def default_layout #:nodoc: @default_layout ||= read_inheritable_attribute("layout") end def layout_list #:nodoc: view_paths.collect do |path| Dir["#{path}/layouts/**/*"] end.flatten end private def inherited_with_layout(child) inherited_without_layout(child) layout_match = child.name.underscore.sub(/_controller$/, '').sub(/^controllers\//, '') child.layout(layout_match) unless child.layout_list.grep(%r{layouts/#{layout_match}(\.[a-z][0-9a-z]*)+$}).empty? 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 def layout_directory_exists_cache @@layout_directory_exists_cache ||= Hash.new do |h, dirname| h[dirname] = File.directory? dirname end 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 active_layout = case layout when String then layout when Symbol then send(layout) when Proc then layout.call(self) end # Explicitly passed layout names with slashes are looked up relative to the template root, # but auto-discovered layouts derived from a nested controller will contain a slash, though be relative # to the 'layouts' directory so we have to check the file system to infer which case the layout name came from. if active_layout if active_layout.include?('/') && ! layout_directory?(active_layout) active_layout else "layouts/#{active_layout}" end end end protected def render_with_a_layout(options = nil, &block) #:nodoc: if template_with_options = options.is_a?(Hash) response.template.template_format = options[:content_type].to_sym if options[:content_type] end if apply_layout?(template_with_options, options) && (layout = pick_layout(template_with_options, options)) assert_existence_of_template_file(layout) options = options.merge :layout => false if template_with_options logger.info("Rendering template within #{layout}") if logger content_for_layout = render_with_no_layout(options, &block) erase_render_results add_variables_to_assigns @template.instance_variable_set("@content_for_layout", content_for_layout) response.layout = layout status = template_with_options ? options[:status] : nil render_for_text(@template.render_file(layout, true), status) else render_with_no_layout(options, &block) end end private def apply_layout?(template_with_options, options) return false if options == :update template_with_options ? candidate_for_layout?(options) : !template_exempt_from_layout? end def candidate_for_layout?(options) (options.has_key?(:layout) && options[:layout] != false) || options.values_at(:text, :xml, :json, :file, :inline, :partial, :nothing).compact.empty? && !template_exempt_from_layout?(default_template_name(options[:action] || options[:template])) end def pick_layout(template_with_options, options) if template_with_options case layout = options[:layout] when FalseClass nil when NilClass, TrueClass active_layout if action_has_layout? else active_layout(layout) end else active_layout if action_has_layout? 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 # Does a layout directory for this class exist? # we cache this info in a class level hash def layout_directory?(layout_name) view_paths.find do |path| next unless template_path = Dir[File.join(path, 'layouts', layout_name) + ".*"].first self.class.send(:layout_directory_exists_cache)[File.dirname(template_path)] end end end end