Calling #content_for
stores a block of markup in an identifier for later use. In order to access
this stored content in other templates, helper modules or the layout, you
would pass the identifier as an argument to content_for.
Note: yield can still be used to retrieve the stored content,
but calling yield doesn't work in helper modules, while
content_for does.
<% content_for :not_authorized do %>
alert('You are not authorized to do that!')
<% end %>You can then use content_for :not_authorized anywhere in your
templates.
<%= content_for :not_authorized if current_user.nil? %>
This is equivalent to:
<%= yield :not_authorized if current_user.nil? %>
content_for, however, can also be used in helper modules.
module StorageHelper
def stored_content
content_for(:storage) || "Your storage is empty"
end
end
This helper works just like normal helpers.
<%= stored_content %>
You can also use the yield syntax alongside an existing call
to yield 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 script identifier.
<%# This is our view %>
Please login!
<% content_for :script do %>
<script>alert('You are not authorized to view this page!')</script>
<% end %>Then, in another view, you could to do something like this:
<%= link_to 'Logout', action: 'logout', remote: true %> <% content_for :script do %> <%= javascript_include_tag :defaults %> <% end %>
That will place script tags for your default set of JavaScript
files on the page; this technique is useful if you'll only be using
these scripts in a few views.
Note that #content_for concatenates (default) 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 %> And in other place: <% 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><%= content_for :navigation %></ul>
If the flush parameter is true #content_for replaces the blocks it is given. 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, flush: true do %> <li><%= link_to 'Login', action: 'login' %></li> <% end %>
Then, in another template or layout, this code would render only the last link:
<ul><%= content_for :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.
Please login to continue.