module ActionController #:nodoc:
module Layout #:nodoc:
def self.append_features(base)
super
base.class_eval do
alias_method :render_without_layout, :render
alias_method :render, :render_with_layout
class << self
alias_method :inherited_without_layout, :inherited
end
end
base.extend(ClassMethods)
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 is only mentioned in one place, like this:
#
# <!-- The header part of this layout -->
# <%= @content_for_layout %>
# <!-- 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:
#
# <h1><%= @page_title %></h1>
# <%= @content_for_layout %>
#
# ...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.rhtml</tt> or <tt>app/views/layouts/weblog.rxml</tt> exists then it will be automatically set as
# the layout for your WeblogController. You can create a layout with the name <tt>application.rhtml</tt> or <tt>application.rxml</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. Setting a layout explicitly will always override the automatic behaviour.
#
# == 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 <tt>render_with_layout</tt> 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_with_layout "help/index", "200", "layouts/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.
module ClassMethods
# If a layout is specified, all actions rendered through render and render_action will have their result assigned
# to <tt>@content_for_layout</tt>, which can then be used by the layout to insert their contents with
# <tt><%= @content_for_layout %></tt>. 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:
read_inheritable_attribute("layout_conditions")
end
private
def inherited(child)
inherited_without_layout(child)
child.layout(child.controller_name) unless layout_list.grep(/^#{child.controller_name}\.r(?:x|ht)ml$/).empty?
end
def layout_list
Dir.glob("#{template_root}/layouts/*.r{x,ht}ml").map { |layout| File.basename(layout) }
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.read_inheritable_attribute("layout")
active_layout = case layout
when Symbol then send(layout)
when Proc then layout.call(self)
when String then layout
end
active_layout.include?("/") ? active_layout : "layouts/#{active_layout}" if active_layout
end
def render_with_layout(template_name = default_template_name, status = nil, layout = nil) #:nodoc:
if layout ||= active_layout and action_has_layout?
add_variables_to_assigns
logger.info("Rendering #{template_name} within #{layout}") unless logger.nil?
@content_for_layout = @template.render_file(template_name, true)
render_without_layout(layout, status)
else
render_without_layout(template_name, status)
end
end
private
def action_has_layout?
conditions = self.class.layout_conditions
case
when conditions[:only]
conditions[:only].include?(action_name)
when conditions[:except]
!conditions[:except].include?(action_name)
else
true
end
end
end
end
