Action View templates can be written in three ways. If the template file has a +.erb+ (or +.rhtml+) extension then it uses a mixture of ERb (included in Ruby) and HTML. If the template file has a +.builder+ (or +.rxml+) extension then Jim Weirich‘s Builder::XmlMarkup library is used. If the template file has a +.rjs+ extension then it will use ActionView::Helpers::PrototypeHelper::JavaScriptGenerator.
You trigger ERb by using embeddings such as <% %>, <% -%>, and <%= %>. The <%= %> tag set is used when you want output. Consider the following loop for names:
<b>Names of all the people</b> <% for person in @people %> Name: <%= person.name %><br/> <% end %>
The loop is setup in regular embedding tags <% %> and the name is written using the output embedding tag <%= %>. Note that this is not just a usage suggestion. Regular output functions like print or puts won‘t work with ERb templates. So this would be wrong:
Hi, Mr. <% puts "Frodo" %>
If you absolutely must write from within a function, you can use the TextHelper#concat
<%- and -%> suppress leading and trailing whitespace, including the trailing newline, and can be used interchangeably with <% and %>.
Using sub templates allows you to sidestep tedious replication and extract common display structures in shared templates. The classic example is the use of a header and footer (even though the Action Pack-way would be to use Layouts):
<%= render "shared/header" %> Something really specific and terrific <%= render "shared/footer" %>
As you see, we use the output embeddings for the render methods. The render call itself will just return a string holding the result of the rendering. The output embedding writes it to the current template.
But you don‘t have to restrict yourself to static includes. Templates can share variables amongst themselves by using instance variables defined using the regular embedding tags. Like this:
<% @page_title = "A Wonderful Hello" %> <%= render "shared/header" %>
Now the header can pick up on the @page_title variable and use it for outputting a title tag:
<title><%= @page_title %></title>
You can pass local variables to sub templates by using a hash with the variable names as keys and the objects as values:
<%= render "shared/header", { :headline => "Welcome", :person => person } %>
These can now be accessed in shared/header with:
Headline: <%= headline %> First name: <%= person.first_name %>
If you need to find out whether a certain local variable has been assigned a value in a particular render call, you need to use the following pattern:
<% if local_assigns.has_key? :headline %> Headline: <%= headline %> <% end %>
Testing using defined? headline will not work. This is an implementation restriction.
By default, Rails will compile each template to a method in order to render it. When you alter a template, Rails will check the file‘s modification time and recompile it.
Builder templates are a more programmatic alternative to ERb. They are especially useful for generating XML content. An XmlMarkup object named xml is automatically made available to templates with a +.builder+ extension.
Here are some basic examples:
xml.em("emphasized") # => <em>emphasized</em> xml.em { xml.b("emph & bold") } # => <em><b>emph & bold</b></em> xml.a("A Link", "href"=>"http://onestepback.org") # => <a href="http://onestepback.org">A Link</a> xml.target("name"=>"compile", "option"=>"fast") # => <target option="fast" name="compile"\> # NOTE: order of attributes is not specified.
Any method with a block will be treated as an XML markup tag with nested markup in the block. For example, the following:
xml.div { xml.h1(@person.name) xml.p(@person.bio) }
would produce something like:
<div> <h1>David Heinemeier Hansson</h1> <p>A product of Danish Design during the Winter of '79...</p> </div>
A full-length RSS example actually used on Basecamp:
xml.rss("version" => "2.0", "xmlns:dc" => "http://purl.org/dc/elements/1.1/") do xml.channel do xml.title(@feed_title) xml.link(@url) xml.description "Basecamp: Recent items" xml.language "en-us" xml.ttl "40" for item in @recent_items xml.item do xml.title(item_title(item)) xml.description(item_description(item)) if item_description(item) xml.pubDate(item_pubDate(item)) xml.guid(@person.firm.account.url + @recent_items.url(item)) xml.link(@person.firm.account.url + @recent_items.url(item)) xml.tag!("dc:creator", item.author_name) if item_has_creator?(item) end end end end
More builder documentation can be found at builder.rubyforge.org.
JavaScriptGenerator templates end in +.rjs+. Unlike conventional templates which are used to render the results of an action, these templates generate instructions on how to modify an already rendered page. This makes it easy to modify multiple elements on your page in one declarative Ajax response. Actions with these templates are called in the background with Ajax and make updates to the page where the request originated from.
An instance of the JavaScriptGenerator object named page is automatically made available to your template, which is implicitly wrapped in an ActionView::Helpers::PrototypeHelper#update_page block.
When an .rjs action is called with link_to_remote, the generated JavaScript is automatically evaluated. Example:
link_to_remote :url => {:action => 'delete'}
The subsequently rendered +delete.rjs+ might look like:
page.replace_html 'sidebar', :partial => 'sidebar' page.remove "person-#{@person.id}" page.visual_effect :highlight, 'user-list'
This refreshes the sidebar, removes a person element and highlights the user list.
See the ActionView::Helpers::PrototypeHelper::GeneratorMethods documentation for more details.
assigns | [RW] | |
base_path | [RW] | |
controller | [RW] | |
first_render | [R] | |
headers | [R] | |
logger | [R] | |
response | [R] | |
template_extension | [RW] | |
template_format | [W] | |
view_paths | [RW] |
# File vendor/rails/actionpack/lib/action_view/base.rb, line 255 255: def self.handler_for_extension(extension) 256: (extension && @@template_handlers[extension.to_sym]) || @@default_template_handlers 257: end
# File vendor/rails/actionpack/lib/action_view/base.rb, line 250 250: def self.register_default_template_handler(extension, klass) 251: register_template_handler(extension, klass) 252: @@default_template_handlers = klass 253: end
Register a class that knows how to handle template files with the given extension. This can be used to implement new template types. The constructor for the class must take the ActiveView::Base instance as a parameter, and the class must implement a render method that takes the contents of the template to render as well as the Hash of local assigns available to the template. The render method ought to return the rendered template as a string.
# File vendor/rails/actionpack/lib/action_view/base.rb, line 242 242: def self.register_template_handler(extension, klass) 243: @@template_handlers[extension.to_sym] = klass 244: end
# File vendor/rails/actionpack/lib/action_view/base.rb, line 246 246: def self.template_handler_extensions 247: @@template_handler_extensions ||= @@template_handlers.keys.map(&:to_s).sort 248: end
Adds a view_path to the end of the view_paths array. This change affects the current request only.
@template.append_view_path("views/default") @template.append_view_path(["views/default", "views/custom"])
# File vendor/rails/actionpack/lib/action_view/base.rb, line 440 440: def append_view_path(path) 441: @view_paths.push(*path) 442: end
Gets the full template path with base path for the given template_path and extension.
full_template_path('users/show', 'html.erb') # => '~/rails/app/views/users/show.html.erb
# File vendor/rails/actionpack/lib/action_view/base.rb, line 378 378: def full_template_path(template_path, extension) 379: if @@cache_template_extensions 380: (@@cached_base_paths[template_path] ||= {})[extension.to_s] ||= find_full_template_path(template_path, extension) 381: else 382: find_full_template_path(template_path, extension) 383: end 384: end
Adds a view_path to the front of the view_paths array. This change affects the current request only.
@template.prepend_view_path("views/default") @template.prepend_view_path(["views/default", "views/custom"])
# File vendor/rails/actionpack/lib/action_view/base.rb, line 430 430: def prepend_view_path(path) 431: @view_paths.unshift(*path) 432: end
symbolized version of the :format parameter of the request, or :html by default.
# File vendor/rails/actionpack/lib/action_view/base.rb, line 418 418: def template_format 419: return @template_format if @template_format 420: format = controller && controller.respond_to?(:request) && controller.request.parameters[:format] 421: @template_format = format.blank? ? :html : format.to_sym 422: end