Rails 2.2 Templates

TemplateHandlers have been significantly overhauled in Rails 2.2, and these changes are not backwards-compatible with Rails 2.1.

Instead of being responsible for rendering a template, TemplateHandlers should now provide a string of Ruby that will be eval’ed by ActionView further along the rendering chain.

So, where previously a TemplateHandler might have declared a render method:

class DotHandler < ActionView::TemplateHandlers::ERB

  def render(template, local_assigns = {})
    @view.controller.headers["Content-Type"] ||= 'image/png'

    input = super(template)

    output = IO.popen('dot -Tpng', 'r+') do |io|
      io.write(input)
      io.close_write
      io.read
    end

    output
  end
end

ActionView::Template::register_template_handler 'dot', DotHandler
ActionController::Base.exempt_from_layout :dot

Templates should now provide a compile method that will return ruby code for execution later:

class DotHandler < ActionView::TemplateHandler

  def compile(path)
    <<-EOS
      controller.response.content_type ||= Mime::PNG
      #{ActionView::Template.handler_class_for_extension('erb').call(path)}
      @output_buffer = IO.popen("dot -Tpng", 'r+') do |io|
      io.write(@output_buffer)
      io.close_write
      io.read
      end
    EOS
  end

end

ActionView::Template.register_template_handler 'dot', DotHandler
ActionView::Template.exempt_from_layout 'dot'

To chain template handlers, find the appropriate handler with ActionView::Template#handler_class_for_extension and then call it. The code it returns can then be injected into your compiled template.