module ActionView
module Helpers
# CaptureHelper exposes methods to let you extract generated markup which
# can be used in other parts of a template or layout file.
# It provides a method to capture blocks into variables through capture and
# a way to capture a block of code for use in a layout through content_for.
module CaptureHelper
# The capture method allows you to extract a part of the template into a
# variable. You can then use this value anywhere in your templates or layout.
#
# ==== Examples
# The capture method can be used in RHTML (ERb) templates...
#
# <% @greeting = capture do %>
# Welcome to my shiny new web page! The date and time is
# <%= Time.now %>
# <% end %>
#
# ...and Builder (RXML) templates.
#
# @timestamp = capture do
# "The current timestamp is #{Time.now}."
# end
#
# You can then use the content as a variable anywhere else. For
# example:
#
#
# <%= @greeting %>
#
# <%= @greeting %>
#
#
def capture(*args, &block)
# execute the block
begin
buffer = eval(ActionView::Base.erb_variable, block.binding)
rescue
buffer = nil
end
if buffer.nil?
capture_block(*args, &block).to_s
else
capture_erb_with_buffer(buffer, *args, &block).to_s
end
end
# Calling content_for stores the block of markup in an identifier for later use.
# You can make subsequent calls to the stored content in another template or in the layout
# by calling it by name with yield.
#
# ==== Examples
#
# <% content_for("authorized") do %>
# alert('You are not authorized for that!')
# <% end %>
#
# You can then use yield :authorized anywhere in your templates.
#
# <%= yield :authorized if current_user == nil %>
#
# You can also use these variables in a layout. For example:
#
#
#
#
# My Website
# <%= yield :script %>
#
#
# <%= yield %>
#
#
#
# And now we'll create a view that has a content_for call that
# creates the script identifier.
#
#
# Please login!
#
# <% content_for("script") do %>
#
# <% end %>
#
# Then in another view you may want to do something like this:
#
# <%= link_to_remote 'Logout', :action => 'logout' %>
#
# <% content_for("script") do %>
# <%= javascript_include_tag :defaults %>
# <% end %>
#
# That will include Prototype and Scriptaculous into the page; this technique
# is useful if you'll only be using these scripts on a few views.
#
# NOTE: Beware that content_for is ignored in caches. So you shouldn't use it
# for elements that are going to be fragment cached.
#
# The deprecated way of accessing a content_for block was to use a instance variable
# named @@content_for_#{name_of_the_content_block}@. So <%= content_for('footer') %>
# would be avaiable as <%= @content_for_footer %>. The preferred notation now is
# <%= yield :footer %>.
def content_for(name, content = nil, &block)
eval "@content_for_#{name} = (@content_for_#{name} || '') + capture(&block)"
end
private
def capture_block(*args, &block)
block.call(*args)
end
def capture_erb(*args, &block)
buffer = eval(ActionView::Base.erb_variable, block.binding)
capture_erb_with_buffer(buffer, *args, &block)
end
def capture_erb_with_buffer(buffer, *args, &block)
pos = buffer.length
block.call(*args)
# extract the block
data = buffer[pos..-1]
# replace it in the original with empty string
buffer[pos..-1] = ''
data
end
def erb_content_for(name, &block)
eval "@content_for_#{name} = (@content_for_#{name} || '') + capture_erb(&block)"
end
def block_content_for(name, &block)
eval "@content_for_#{name} = (@content_for_#{name} || '') + capture_block(&block)"
end
end
end
end