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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 markup for use in a layout through content_for.
module CaptureHelper
# The capture method allows you to extract part of a template into a
# variable. You can then use this variable anywhere in your templates or layout.
#
# ==== Examples
# The capture method can be used in 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 that 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 a block of markup in an identifier for later use.
# You can make subsequent calls to the stored content in other templates or the layout
# by passing the identifier as an argument to <tt>yield</tt>.
#
# ==== Examples
#
# <% content_for :not_authorized do %>
# alert('You are not authorized to do that!')
# <% end %>
#
# You can then use <tt>yield :not_authorized</tt> anywhere in your templates.
#
# <%= yield :not_authorized if current_user.nil? %>
#
# You can also use this syntax alongside an existing call to <tt>yield</tt> 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 to view this page!')</script>
# <% end %>
#
# Then, in another view, you could to do something like this:
#
# <%= link_to_remote 'Logout', :action => 'logout' %>
#
# <% content_for :script do %>
# <%= javascript_include_tag :defaults %>
# <% end %>
#
# That will place <script> tags for Prototype, Scriptaculous, and application.js (if it exists)
# on the page; this technique is useful if you'll only be using these scripts in a few views.
#
# Note that content_for concatenates the blocks it is given for a particular
# identifier in order. For example:
#
# <% content_for :navigation do %>
# <li><%= link_to 'Home', :action => 'index' %></li>
# <% end %>
#
# <%# Add some other content, or use a different template: %>
#
# <% content_for :navigation do %>
# <li><%= link_to 'Login', :action => 'login' %></li>
# <% end %>
#
# Then, in another template or layout, this code would render both links in order:
#
# <ul><%= yield :navigation %></ul>
#
# Lastly, simple content can be passed as a parameter:
#
# <% content_for :script, javascript_include_tag(:defaults) %>
#
# WARNING: content_for is ignored in caches. So you shouldn't use it
# for elements that will be fragment cached.
#
# The deprecated way of accessing a content_for block is to use an instance variable
# named <tt>@content_for_#{name_of_the_content_block}</tt>. The preferred usage is now
# <tt><%= yield :footer %></tt>.
def content_for(name, content = nil, &block)
existing_content_for = instance_variable_get("@content_for_#{name}").to_s
new_content_for = existing_content_for + (block_given? ? capture(&block) : content)
instance_variable_set("@content_for_#{name}", new_content_for)
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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