rails标签值content_tag

 今天阅读《Agile Web Development with Rails》时碰到下面的一段代码比较疑惑

#Download depot_n/app/views/layouts/application.html.erb

<%= hidden_div_if(@cart.line_items.empty?, :id => "cart" ) do %>

    <%= render @cart %>

<% end %>



#Download depot_n/app/helpers/application_helper.rb

module ApplicationHelper

  def hidden_div_if(condition, attributes = {}, &block)

    if condition

      attributes["style" ] = "display: none"

    end

    content_tag("div" , attributes, &block)

  end

end

主要是对content_tag标签和&block合用不怎么明白，先去看看源码上的说明文档。

 1       # Returns an HTML block tag of type +name+ surrounding the +content+. Add
 2       # HTML attributes by passing an attributes hash to +options+.
 3       # Instead of passing the content as an argument, you can also use a block
 4       # in which case, you pass your +options+ as the second parameter.
 5       # Set escape to false to disable attribute value escaping.
 6       #
 7       # ==== Options
 8       # The +options+ hash is used with attributes with no value like (<tt>disabled</tt> and
 9       # <tt>readonly</tt>), which you can give a value of true in the +options+ hash. You can use
10       # symbols or strings for the attribute names.
11       #
12       # ==== Examples
13       #   content_tag(:p, "Hello world!")
14       #    # => <p>Hello world!</p>
15       #   content_tag(:div, content_tag(:p, "Hello world!"), :class => "strong")
16       #    # => <div class="strong"><p>Hello world!</p></div>
17       #   content_tag("select", options, :multiple => true)
18       #    # => <select multiple="multiple">...options...</select>
19       #
20       #   <%= content_tag :div, :class => "strong" do -%>
21       #     Hello world!
22       #   <% end -%>
23       #    # => <div class="strong">Hello world!</div>

从上述我们可以看到content_tag("div" , attributes, &block)中的div为标签信息，attributes为style信息，那么&block是什么意思呢？

在看个示例

 1 #http://api.rubyonrails.org/classes/ActionView/Helpers/RecordTagHelper.html
 2 
 3 div_for(record, *args, &block)
 4 
 5 Produces a wrapper DIV element with id and class parameters that relate to the specified Active Record object. Usage example:
 6 
 7 <%= div_for(@person, :class => "foo") do %>
 8    <%=h @person.name %>
 9 <% end %>
10 
11 produces:
12 
13 <div id="person_123" class="person foo"> Joe Bloggs </div>

大概的意思明白了，content_tag("div" , attributes, &block)这句话就可以翻译成下面的代码

<div id=“cart">

   <% render @cart%>

</div>