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module ActionController
# 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:
#
# <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
#
# == 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 <tt>app/views/layouts</tt>.
# 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 <tt>app/views/layouts/posts.html.erb</tt>,
# 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
# <tt>app/views/layouts/weblog/posts.html.erb</tt>.
#
# Since all your controllers inherit from ApplicationController, they will use
# <tt>app/views/layouts/application.html.erb</tt> if no other layout is specified
# or provided.
#
# == Inheritance Examples
#
# class BankController < ActionController::Base
# layout "bank_standard"
#
# class InformationController < BankController
#
# class TellerController < BankController
# # teller.html.erb exists
#
# class TillController < TellerController
#
# 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.
#
# The TellerController uses +teller.html.erb+, and TillController inherits that layout and
# uses it as well.
#
# == 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 Layouts
extend ActiveSupport::Concern
include ActionController::Rendering
include AbstractController::Layouts
module ClassMethods
# If no layout is provided, look for a layout with this name.
def _implied_layout_name
controller_path
end
end
end
end
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