require "action_view/rendering" require "active_support/core_ext/module/remove_method" module ActionView # 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 # # bank.html.erb exists # # class ExchangeController < BankController # # exchange.html.erb exists # # class CurrencyController < BankController # # class InformationController < BankController # layout "information" # # class TellerController < InformationController # # teller.html.erb exists # # class EmployeeController < InformationController # # employee.html.erb exists # layout nil # # class VaultController < BankController # layout :access_level_layout # # class TillController < BankController # layout false # # In these examples, we have three implicit lookup scenarios: # * The BankController uses the "bank" layout. # * The ExchangeController uses the "exchange" layout. # * The CurrencyController inherits the layout from BankController. # # However, when a layout is explicitly set, the explicitly set layout wins: # * The InformationController uses the "information" layout, explicitly set. # * The TellerController also uses the "information" layout, because the parent explicitly set it. # * The EmployeeController uses the "employee" layout, because it set the layout to nil, resetting the parent configuration. # * The VaultController chooses a layout dynamically by calling the access_level_layout method. # * The TillController does not 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 # 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" } # end # # If an argument isn't given to the proc, it's evaluated in the context of # the current controller anyway. # # class WeblogController < ActionController::Base # layout proc { logged_in? ? "writer_layout" : "reader_layout" } # end # # 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" # end # # The template will be looked always in app/views/layouts/ folder. But you can point # layouts folder direct also. layout "layouts/demo" is the same as layout "demo". # # Setting the layout to nil forces it to be looked up in the filesystem and fallbacks to the parent behavior if none exists. # Setting it to nil is useful to re-enable template lookup overriding a previous configuration set in the parent: # # class ApplicationController < ActionController::Base # layout "application" # end # # class PostsController < ApplicationController # # Will use "application" layout # end # # class CommentsController < ApplicationController # # Will search for "comments" layout and fallback "application" layout # layout nil # end # # == 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 for all actions except for the +rss+ action, which will # be rendered directly, without wrapping 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 override the controller-wide "weblog_standard" layout, and will render the help action with the "help" layout instead. module Layouts extend ActiveSupport::Concern include ActionView::Rendering included do class_attribute :_layout, :_layout_conditions, :instance_accessor => false self._layout = nil self._layout_conditions = {} _write_layout_method end delegate :_layout_conditions, to: :class module ClassMethods def inherited(klass) # :nodoc: super klass._write_layout_method end # This module is mixed in if layout conditions are provided. This means # that if no layout conditions are used, this method is not used module LayoutConditions # :nodoc: private # Determines whether the current action has a layout definition by # checking the action name against the :only and :except conditions # set by the layout method. # # ==== Returns # * Boolean - True if the action has a layout definition, false otherwise. def _conditional_layout? return unless super conditions = _layout_conditions if only = conditions[:only] only.include?(action_name) elsif except = conditions[:except] !except.include?(action_name) else true end end end # Specify the layout to use for this class. # # If the specified layout is a: # String:: the String is the template name # Symbol:: call the method specified by the symbol, which will return the template name # false:: There is no layout # true:: raise an ArgumentError # nil:: Force default layout behavior with inheritance # # ==== Parameters # * layout - The layout to use. # # ==== Options (conditions) # * :only - A list of actions to apply this layout to. # * :except - Apply this layout to all actions but this one. def layout(layout, conditions = {}) include LayoutConditions unless conditions.empty? conditions.each {|k, v| conditions[k] = Array(v).map {|a| a.to_s} } self._layout_conditions = conditions self._layout = layout _write_layout_method end # If no layout is supplied, look for a template named the return # value of this method. # # ==== Returns # * String - A template name def _implied_layout_name # :nodoc: controller_path end # Creates a _layout method to be called by _default_layout . # # If a layout is not explicitly mentioned then look for a layout with the controller's name. # if nothing is found then try same procedure to find super class's layout. def _write_layout_method # :nodoc: remove_possible_method(:_layout) prefixes = _implied_layout_name =~ /\blayouts/ ? [] : ["layouts"] default_behavior = "lookup_context.find_all('#{_implied_layout_name}', #{prefixes.inspect}).first || super" name_clause = if name default_behavior else <<-RUBY super RUBY end layout_definition = case _layout when String _layout.inspect when Symbol <<-RUBY #{_layout}.tap do |layout| return #{default_behavior} if layout.nil? unless layout.is_a?(String) || !layout raise ArgumentError, "Your layout method :#{_layout} returned \#{layout}. It " \ "should have returned a String, false, or nil" end end RUBY when Proc define_method :_layout_from_proc, &_layout protected :_layout_from_proc <<-RUBY result = _layout_from_proc(#{_layout.arity == 0 ? '' : 'self'}) return #{default_behavior} if result.nil? result RUBY when false nil when true raise ArgumentError, "Layouts must be specified as a String, Symbol, Proc, false, or nil" when nil name_clause end self.class_eval <<-RUBY, __FILE__, __LINE__ + 1 def _layout if _conditional_layout? #{layout_definition} else #{name_clause} end end private :_layout RUBY end end def _normalize_options(options) # :nodoc: super if _include_layout?(options) layout = options.delete(:layout) { :default } options[:layout] = _layout_for_option(layout) end end attr_internal_writer :action_has_layout def initialize(*) # :nodoc: @_action_has_layout = true super end # Controls whether an action should be rendered using a layout. # If you want to disable any layout settings for the # current action so that it is rendered without a layout then # either override this method in your controller to return false # for that action or set the action_has_layout attribute # to false before rendering. def action_has_layout? @_action_has_layout end private def _conditional_layout? true end # This will be overwritten by _write_layout_method def _layout; end # Determine the layout for a given name, taking into account the name type. # # ==== Parameters # * name - The name of the template def _layout_for_option(name) case name when String then _normalize_layout(name) when Proc then name when true then Proc.new { _default_layout(true) } when :default then Proc.new { _default_layout(false) } when false, nil then nil else raise ArgumentError, "String, Proc, :default, true, or false, expected for `layout'; you passed #{name.inspect}" end end def _normalize_layout(value) value.is_a?(String) && value !~ /\blayouts/ ? "layouts/#{value}" : value end # Returns the default layout for this controller. # Optionally raises an exception if the layout could not be found. # # ==== Parameters # * require_layout - If set to true and layout is not found, # an ArgumentError exception is raised (defaults to false) # # ==== Returns # * template - The template object for the default layout (or nil) def _default_layout(require_layout = false) begin value = _layout if action_has_layout? rescue NameError => e raise e, "Could not render layout: #{e.message}" end if require_layout && action_has_layout? && !value raise ArgumentError, "There was no default layout for #{self.class} in #{view_paths.inspect}" end _normalize_layout(value) end def _include_layout?(options) (options.keys & [:text, :inline, :partial]).empty? || options.key?(:layout) end end end