Module | ActionView::Helpers::CaptureHelper |
In: |
vendor/rails/actionpack/lib/action_view/helpers/capture_helper.rb
|
Capture lets you extract parts of code which can be used in other points of the template or even layout file.
<% @script = capture do %> [some html...] <% end %>
content_for("name") is a wrapper for capture which will make the fragment available by name to a yielding layout or template.
layout.rhtml:
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <title>layout with js</title> <script type="text/javascript"> <%= yield :script %> </script> </head> <body> <%= yield %> </body> </html>
view.rhtml
This page shows an alert box! <% content_for("script") do %> alert('hello world') <% end %> Normal view text
Capture allows you to extract a part of the template into an instance variable. You can use this instance variable anywhere in your templates and even in your layout.
Example of capture being used in a .rhtml page:
<% @greeting = capture do %> Welcome To my shiny new web page! <% end %>
Example of capture being used in a .rxml page:
@greeting = capture do 'Welcome To my shiny new web page!' end
# File vendor/rails/actionpack/lib/action_view/helpers/capture_helper.rb, line 56 56: def capture(*args, &block) 57: # execute the block 58: begin 59: buffer = eval("_erbout", block.binding) 60: rescue 61: buffer = nil 62: end 63: 64: if buffer.nil? 65: capture_block(*args, &block) 66: else 67: capture_erb_with_buffer(buffer, *args, &block) 68: end 69: end
Calling content_for stores the block of markup for later use. Subsequently, you can make calls to it by name with yield in another template or in the layout.
Example:
<% content_for("header") do %> alert('hello world') <% end %>
You can use yield :header anywhere in your templates.
<%= yield :header %>
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 %>.
# File vendor/rails/actionpack/lib/action_view/helpers/capture_helper.rb, line 92 92: def content_for(name, &block) 93: eval "@content_for_#{name} = (@content_for_#{name} || '') + capture(&block)" 94: end