Action View Capture 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
.
As well as provides a method when using streaming responses through provide
. See ActionController::Streaming
for more information.
Instance Public methods
capture(*args, &block) Link
The capture method extracts part of a template as a string object. You can then use this object anywhere in your templates, layout, or helpers.
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>
The return of capture is the string generated by the block. For Example:
@greeting # => "Welcome to my shiny new web page! The date and time is 2018-09-06 11:09:16 -0500"
# File actionview/lib/action_view/helpers/capture_helper.rb, line 47 def capture(*args, &block) value = nil @output_buffer ||= ActionView::OutputBuffer.new buffer = @output_buffer.capture { value = yield(*args) } string = if @output_buffer.equal?(value) buffer else buffer.presence || value end case string when OutputBuffer string.to_s when ActiveSupport::SafeBuffer string when String ERB::Util.html_escape(string) end end
content_for(name, content = nil, options = {}, &block) Link
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 another 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.
# File actionview/lib/action_view/helpers/capture_helper.rb, line 172 def content_for(name, content = nil, options = {}, &block) if content || block_given? if block_given? options = content if content content = capture(&block) end if content options[:flush] ? @view_flow.set(name, content) : @view_flow.append(name, content) end nil else @view_flow.get(name).presence end end
content_for?(name) Link
content_for?
checks whether any content has been captured yet using content_for
.
Useful to render parts of your layout differently based on what is in your views.
<%# 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 class="<%= content_for?(:right_col) ? 'two-column' : 'one-column' %>">
<%= yield %>
<%= yield :right_col %>
</body>
</html>
provide(name, content = nil, &block) Link
The same as content_for
but when used with streaming flushes straight back to the layout. In other words, if you want to concatenate several times to the same buffer when rendering a given template, you should use content_for
, if not, use provide
to tell the layout to stop looking for more contents.
See ActionController::Streaming
for more information.