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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:
#
# <html>
# <head><title><%= @greeting %></title></head>
# <body>
# <b><%= @greeting %></b>
# </body></html>
#
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 <tt>yield</tt>.
#
# ==== Examples
#
# <% content_for("authorized") do %>
# alert('You are not authorized for that!')
# <% end %>
#
# You can then use <tt>yield :authorized</tt> anywhere in your templates.
#
# <%= yield :authorized if current_user == nil %>
#
# You can also use these variables in a layout. For example:
#
# <!-- This is the layout -->
# <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
# <head>
# <title>My Website</title>
# <%= yield :script %>
# </head>
# <body>
# <%= yield %>
# </body>
# </html>
#
# And now we'll create a view that has a content_for call that
# creates the <tt>script</tt> identifier.
#
# <!-- This is our view -->
# Please login!
#
# <% content_for("script") do %>
# <script type="text/javascript">alert('You are not authorized for this action!')</script>
# <% 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 <tt><%= content_for('footer') %></tt>
# would be avaiable as <tt><%= @content_for_footer %></tt>. The preferred notation now is
# <tt><%= yield :footer %></tt>.
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
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