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 <tt>@content_for_layout</tt> instance
# variable. The preferred notation now is to use <tt>yield</tt>, 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:
#
# <h1><%= @page_title %></h1>
# <%= 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:
#
# <h1>Welcome</h1>
# Off-world colonies offers you a chance to start a new life
#
# == Automatic layout assignment
#
# If there is a template in <tt>app/views/layouts/</tt> 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
# <tt>app/views/layouts/weblog.erb</tt> or <tt>app/views/layouts/weblog.builder</tt> exists then it will be automatically set as
# the layout for your WeblogController. You can create a layout with the name <tt>application.erb</tt> or <tt>application.builder</tt>
# 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 <tt>app/views/layouts/admin/weblog.erb</tt>.
# 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 <tt>app/views/layouts/</tt>.
# 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
# <tt>:only</tt> and <tt>:except</tt> 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 <tt>:only</tt> and <tt>:except</tt> condition can accept an arbitrary number of method references, so
# #<tt>:except => [ :rss, :text_only ]</tt> is valid, as is <tt>:except => :rss</tt>.
#
# == 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 <tt>:layout</tt> option to the <tt>render</tt> 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 <tt>yield</tt>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 = {}, 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 <tt>layout "weblog/standard"</tt> will return
# weblog/standard, but <tt>layout "standard"</tt> 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
