layout机制（顺便复习模板机制）
在application.html.erb中加入binding.pry
Pragprog Books Online Store
<%= csrf_meta_tags %>
<%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track': 'reload' %>
<%= javascript_include_tag 'application', 'data-turbolinks-track': 'reload' %>
<% binding.pry %>
<%= yield %>
得调用栈如下
[1] pry(#<#>)> _bsi_
=> {0=>#<binding:70045758642500 #<class:0x007f69cf29f9d8="">#_app_views_layouts_application_html_erb___3541629653556534568_70046211675620 /home/z/test_rails/depot/app/views/layouts/application.html.erb:39>,
1=>#<binding:70045759069160 actionview::template#block="" in="" render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" template.rb:159="">,
2=>#<binding:70045759503020 activesupport::notifications.instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" activesupport-5.0.2="" lib="" active_support="" notifications.rb:166="">,
3=>#<binding:70045759928860 actionview::template#instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" template.rb:354="">,
4=>#<binding:70045760340680 actionview::template#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" template.rb:157="">,
5=>#<binding:70045760696120 actionview::templaterenderer#render_with_layout="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:66="">,
6=>#<binding:70045761106380 actionview::templaterenderer#render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:52="">,
7=>#<binding:70045761507620 actionview::templaterenderer#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:14="">,
8=>#<binding:70045761924980 actionview::renderer#render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" renderer.rb:42="">,
9=>#<binding:70045762326140 actionview::renderer#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" renderer.rb:23="">,
10=>#<binding:70045762736120 storecontroller#_render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" rendering.rb:104="">,
11=>#<binding:70045763147920 storecontroller#_render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" streaming.rb:217="">,
12=>#<binding:70045763278200 storecontroller#render_to_body="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" rendering.rb:83="">,
13=>#<binding:70045763450580 storecontroller#render_to_body="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" rendering.rb:52="">,
14=>#<binding:70045763843520 storecontroller#render_to_body="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" renderers.rb:142="">,
15=>#<binding:70045764050280 storecontroller#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" abstract_controller="" rendering.rb:26="">,
16=>#<binding:70045764197340 storecontroller#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" rendering.rb:36="">,
17=>#<binding:70045764518340 storecontroller#block="" (2="" levels)="" in="" render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" instrumentation.rb:44="">,
18=>#<binding:70045765647320 benchmark.block="" in="" ms="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" activesupport-5.0.2="" lib="" active_support="" core_ext="" benchmark.rb:12="">,
19=>#<binding:70045765803580 benchmark.realtime="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" 2.4.0="" benchmark.rb:308="">,
20=>#<binding:70045765911640 benchmark.ms="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" activesupport-5.0.2="" lib="" active_support="" core_ext="" benchmark.rb:12="">,
21=>#<binding:70045765993640 storecontroller#block="" in="" render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" instrumentation.rb:44="">,
22=>#<binding:70045766068960 storecontroller#cleanup_view_runtime="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" instrumentation.rb:87="">,
23=>#<binding:70045767595920 storecontroller#cleanup_view_runtime="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" activerecord-5.0.2="" lib="" active_record="" railties="" controller_runtime.rb:25="">,
24=>#<binding:70045767620700 storecontroller#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" instrumentation.rb:43="">,
25=>#<binding:70045767654740 storecontroller#default_render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" implicit_render.rb:36="">,
26=>#<binding:70045765986380 storecontroller#block="" in="" send_action="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" basic_implicit_render.rb:4="">,
27=>#<binding:70045765964560 storecontroller#send_action="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" basic_implicit_render.rb:4="">,
28=>#<binding:70045765950940 storecontroller#process_action="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" abstract_controller="" base.rb:188="">,
29=>#<binding:70045767747820 storecontroller#process_action="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" action_controller="" metal="" rendering.rb:30="">,
30=>#<binding:70045767783320 storecontroller#block="" in="" process_action="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionpack-5.0.2="" lib="" abstract_controller="" callbacks.rb:20="">,</binding:70045767783320></binding:70045767747820></binding:70045765950940></binding:70045765964560></binding:70045765986380></binding:70045767654740></binding:70045767620700></binding:70045767595920></binding:70045766068960></binding:70045765993640></binding:70045765911640></binding:70045765803580></binding:70045765647320></binding:70045764518340></binding:70045764197340></binding:70045764050280></binding:70045763843520></binding:70045763450580></binding:70045763278200></binding:70045763147920></binding:70045762736120></binding:70045762326140></binding:70045761924980></binding:70045761507620></binding:70045761106380></binding:70045760696120></binding:70045760340680></binding:70045759928860></binding:70045759503020></binding:70045759069160></binding:70045758642500> 其上一层，也就是ActionView::Template#block in render，是这样的
def render(view, locals, buffer=nil, &block)
instrument("!render_template".freeze) do
compile!(view)
view.send(method_name, locals, buffer, &block)
end
rescue => e
handle_render_error(view, e)
end如无意外，就跟之前研究过的“sinatra如何利用tilt来render”一样，基本上就是，用erb（如果模板是erb）来将模板转换成一个method，method所绑定的对象（即view），带有controller的实例变量，并且该method可接收额外的局部变量
于是稍微验证一下
首先，compile!所做的就是给view加上method
# actionview-5.0.2/lib/action_view/template.rb
def compile(mod)
encode!
method_name = self.method_name
code = @handler.call(self)
# Make sure that the resulting String to be eval'd is in the
# encoding of the code
source = <<-end_src
def #{method_name}(local_assigns, output_buffer)
_old_virtual_path, @virtual_path = @virtual_path, #{@virtual_path.inspect};_old_output_buffer = @output_buffer;#{locals_code};#{code}
ensure
@virtual_path, @output_buffer = _old_virtual_path, _old_output_buffer
end
end_src
# Make sure the source is in the encoding of the returned code
source.force_encoding(code.encoding)
# In case we get back a String from a handler that is not in
# BINARY or the default_internal, encode it to the default_internal
source.encode!
# Now, validate that the source we got back from the template
# handler is valid in the default_internal. This is for handlers
# that handle encoding but screw up
unless source.valid_encoding?
raise WrongEncodingError.new(@source, Encoding.default_internal)
end
mod.module_eval(source, identifier, 0)
ObjectSpace.define_finalizer(self, Finalizer[method_name, mod])
end而这个method中，生成最终html（如果你是返回html）的code，来自@handler.call(self)。于是检查下handler是啥
[10] pry(#<#>)> _bsi_[1].eval("handler.class")
=> ActionView::Template::Handlers::ERB 其源码如下
# actionview-5.0.2/lib/action_view/template/handlers/erb.rb
def call(template)
# First, convert to BINARY, so in case the encoding is
# wrong, we can still find an encoding tag
# (<%# encoding %>) inside the String using a regular
# expression
template_source = template.source.dup.force_encoding(Encoding::ASCII_8BIT)
erb = template_source.gsub(ENCODING_TAG, '')
encoding = $2
erb.force_encoding valid_encoding(template.source.dup, encoding)
# Always make sure we return a String in the default_internal
erb.encode!
self.class.erb_implementation.new(
erb,
:escape => (self.class.escape_whitelist.include? template.type),
:trim => (self.class.erb_trim_mode == "-")
).src
end而handler则是，初始化view的时候就赋予的（其实这不重要）
# actionview-5.0.2/lib/action_view/template.rb
attr_reader :source, :identifier, :handler, :original_encoding, :updated_at
def initialize(source, identifier, handler, details)
format = details[:format] || (handler.default_format if handler.respond_to?(:default_format))
@source = source
@identifier = identifier
@handler = handler
@compiled = false
@original_encoding = nil
@locals = details[:locals] || []
@virtual_path = details[:virtual_path]
@updated_at = details[:updated_at] || Time.now
@formats = Array(format).map { |f| f.respond_to?(:ref) ? f.ref : f }
@variants = [details[:variant]]
@compile_mutex = Mutex.new
end那么，回到如何找layout的问题上，从调用栈可见，这个过程应是如下
5=>#<binding:70045760696120 actionview::templaterenderer#render_with_layout="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:66="">,
6=>#<binding:70045761106380 actionview::templaterenderer#render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:52="">,
7=>#<binding:70045761507620 actionview::templaterenderer#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:14="">,
8=>#<binding:70045761924980 actionview::renderer#render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" renderer.rb:42="">,
9=>#<binding:70045762326140 actionview::renderer#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" renderer.rb:23="">,</binding:70045762326140></binding:70045761924980></binding:70045761507620></binding:70045761106380></binding:70045760696120>都在TemplateRenderer中
module ActionView
class TemplateRenderer < AbstractRenderer
def render(context, options)
@view = context
@details = extract_details(options)
template = determine_template(options)
prepend_formats(template.formats)
@lookup_context.rendered_format ||= (template.formats.first || formats.first)
render_template(template, options[:layout], options[:locals])
end
def render_template(template, layout_name = nil, locals = nil)
view, locals = @view, locals || {}
render_with_layout(layout_name, locals) do |layout|
instrument(:template, :identifier => template.identifier, :layout => layout.try(:virtual_path)) do
template.render(view, locals) { |*name| view._layout_for(*name) }
end
end
end
def render_with_layout(path, locals)
layout = path && find_layout(path, locals.keys, [formats.first])
content = yield(layout)
if layout
view = @view
view.view_flow.set(:layout, content)
layout.render(view, locals){ |*name| view._layout_for(*name) }
else
content
end
end
end
end那么这里的options[:layout]是什么呢
[13] pry(#<#>)> _bsi_[7].lv(:options)
=> {:prefixes=>["store", "application"], :template=>"index", :layout=>#<proc:0x007f69cf29fd70@ home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" layouts.rb:386="">}</proc:0x007f69cf29fd70@> 这里好像有点不对劲了，才发现现在断点就是在application.html.erb这个layout上，那就不好分析了，还是断在内容上吧，于是
<%= notice %>
Your Pragmatic Catalog
<% @products.each do |product| %>
<%= image_tag(product.image_url) %>
<%= product.title %>
<%= sanitize(product.description) %>
<%= number_to_currency product.price %>
<%= button_to 'Add to Cart', line_items_path(product_id: product), remote: true %>
<% end %>
<% binding.pry %>得调用栈如下
[1] pry(#<#>)> _bsi_
=> {0=>#<binding:70045772081600 #<class:0x007f69cf29f9d8="">#_app_views_store_index_html_erb__2763356708539799932_70045772484440 /home/z/test_rails/depot/app/views/store/index.html.erb:17>,
1=>#<binding:70045772032120 actionview::template#block="" in="" render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" template.rb:159="">,
2=>#<binding:70045771966320 activesupport::notifications.instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" activesupport-5.0.2="" lib="" active_support="" notifications.rb:166="">,
3=>#<binding:70045771908740 actionview::template#instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" template.rb:354="">,
4=>#<binding:70045771842300 actionview::template#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" template.rb:157="">,
5=>#<binding:70045771792900 actionview::templaterenderer#block="" (2="" levels)="" in="" render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:54="">,
6=>#<binding:70045771759860 actionview::templaterenderer#block="" in="" instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" abstract_renderer.rb:42="">,
7=>#<binding:70045771686380 activesupport::notifications.block="" in="" instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" activesupport-5.0.2="" lib="" active_support="" notifications.rb:164="">,
8=>#<binding:70045771621060 activesupport::notifications::instrumenter#instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" activesupport-5.0.2="" lib="" active_support="" notifications="" instrumenter.rb:21="">,
9=>#<binding:70045771555580 activesupport::notifications.instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" activesupport-5.0.2="" lib="" active_support="" notifications.rb:164="">,
10=>#<binding:70045771490240 actionview::templaterenderer#instrument="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" abstract_renderer.rb:41="">,
11=>#<binding:70045771416660 actionview::templaterenderer#block="" in="" render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:53="">,
12=>#<binding:70045771351340 actionview::templaterenderer#render_with_layout="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:61="">,
13=>#<binding:70045771285860 actionview::templaterenderer#render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:52="">,
14=>#<binding:70045771219460 actionview::templaterenderer#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" template_renderer.rb:14="">,
15=>#<binding:70045771143900 actionview::renderer#render_template="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" renderer.rb:42="">,
16=>#<binding:70045771069940 actionview::renderer#render="" home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" renderer="" renderer.rb:23="">,</binding:70045771069940></binding:70045771143900></binding:70045771219460></binding:70045771285860></binding:70045771351340></binding:70045771416660></binding:70045771490240></binding:70045771555580></binding:70045771621060></binding:70045771686380></binding:70045771759860></binding:70045771792900></binding:70045771842300></binding:70045771908740></binding:70045771966320></binding:70045772032120></binding:70045772081600> 但发现options[:layout]仍然是如此一个Proc
[2] pry(#<#>)> _bsi_[14].lv(:options)
=> {:prefixes=>["store", "application"], :template=>"index", :layout=>#<proc:0x007f699ac616b8@ home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" layouts.rb:386="">}
[3] pry(#<#>)> _bsi_[13].lv(:layout_name)
=> #<proc:0x007f699ac616b8@ home="" z="" .rbenv="" versions="" 2.4.0="" lib="" ruby="" gems="" 2.4.0="" gems="" actionview-5.0.2="" lib="" action_view="" layouts.rb:386=""></proc:0x007f699ac616b8@> </proc:0x007f699ac616b8@> 但回过头来看，render_template和render_with_layout分别有以下两句
template.render(view, locals) { |*name| view._layout_for(*name) }
layout.render(view, locals){ |*name| view._layout_for(*name) }于是，大概可以这样猜测：当前的view在render时，会找出layout对象（它也是一个view），然后调用layout的render，并带上一个block，在block中调用当前view的render；当layout所转换成的method中调用yield时，即调用了当前view的render，于是layout便嵌套了当前view。
理论上这是可行的，但真要去验证actionview的具体做法的话……好像太麻烦了，先不干了……