Rails - Apr 2011 - View helper, blocks and capture. Template output is repeated (rails 3)

I''m having some issues with blocks and capture in erb templates, and
the particular problem shows itself in that the expected output in the
template view is repeated due to something related to how capture
works. (Using Rails 3.x)


I have the following view helper:

module ColumnLayoutHelper

  def layout_columns(options = {}, &content_block)
    raise ArgumentError, "No block given" unless block_given?

    layout = ColumnLayoutBuilder.new
    layout.configure(options)
    content = capture(layout, &content_block)
    content_tag(:div, content, layout.main_wrapping, false)

  end

end

class ColumnLayoutBuilder < Object

  include ActionView::Helpers::TagHelper
  include ActionView::Helpers::CaptureHelper

  attr_accessor :output_buffer, :column_counter
  attr_accessor :main_wrapping
  attr_accessor :column_wrapping

  def configure(options)
    @main_wrapping = options.delete(:main_wrapping)
    @column_wrapping = options.delete(:column_wrapping)
  end

  def column(&block)

    raise ArgumentError, "No block given" unless block_given?

    @column_counter ||= 0
    @column_counter = @column_counter + 1

    column_html_options = (column_wrapping ? column_wrapping.dup : {})
|| {}
    column_html_options.default = ""
    column_html_options[:class] = "column_#{column_counter} " +
column_html_options[:class]
    column_content = content_tag(:div, capture(self, &block),
column_html_options,false)
    column_content
  end

end

--

Now if I use this column builder helper with the following erb
template:

<%= layout_columns do |layout|  %>
<%= layout.column do %>
content_01
<% end %>
<%= layout.column do %>
content02
<% end %>
<% end %>


I get the following output.

<div>
  content_01
  <div class="column_1 ">content_01</div>
  content02
  <div class="column_2 ">
    content_01
    <div class="column_1 ">content_01</div>
    content02
  </div>
</div>


As you can see, the buffer in between the captures doesn''t seem to be
cleared in the separate block scopes. As I sort of expected how
capture would work...

I guess I''m having the same issues as pointed out here
http://stackoverflow.com/questions/4352167/cant-suppress-output-in-nested-block-helper-in-rails-3

Any ideas on how to fix this?  Thanks

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On 14 Apr 2011, at 23:26, christoffer
<christoffer.ahlbin-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> I''m having some issues with blocks and capture in erb templates,
and
> the particular problem shows itself in that the expected output in the
> template view is repeated due to something related to how capture
> works. (Using Rails 3.x)
Here''s my hunch: capture swaps in a temporary output buffer to capture
the output. However because you''ve got your custom builder object, the
call to capture inside your builder object is fiddling with the
builder''s output buffer attribute, which is neither here nor there
because the bits of erb you yield to know nothing of this arrangement an d are
writing to the template''s output_buffer

If you look at the source for fields_for/Formbuilder you can see that they
squirrel away the template object (in your helper method this is just self) for
later. You should probably do the same

Fred


> 
> 
> I have the following view helper:
> 
> module ColumnLayoutHelper
> 
>  def layout_columns(options = {}, &content_block)
>    raise ArgumentError, "No block given" unless block_given?
> 
>    layout = ColumnLayoutBuilder.new
>    layout.configure(options)
>    content = capture(layout, &content_block)
>    content_tag(:div, content, layout.main_wrapping, false)
> 
>  end
> 
> end
> 
> class ColumnLayoutBuilder < Object
> 
>  include ActionView::Helpers::TagHelper
>  include ActionView::Helpers::CaptureHelper
> 
>  attr_accessor :output_buffer, :column_counter
>  attr_accessor :main_wrapping
>  attr_accessor :column_wrapping
> 
>  def configure(options)
>    @main_wrapping = options.delete(:main_wrapping)
>    @column_wrapping = options.delete(:column_wrapping)
>  end
> 
>  def column(&block)
> 
>    raise ArgumentError, "No block given" unless block_given?
> 
>    @column_counter ||= 0
>    @column_counter = @column_counter + 1
> 
>    column_html_options = (column_wrapping ? column_wrapping.dup : {})
> || {}
>    column_html_options.default = ""
>    column_html_options[:class] = "column_#{column_counter} " +
> column_html_options[:class]
>    column_content = content_tag(:div, capture(self, &block),
> column_html_options,false)
>    column_content
>  end
> 
> end
> 
> --
> 
> Now if I use this column builder helper with the following erb
> template:
> 
> <%= layout_columns do |layout|  %>
> <%= layout.column do %>
> content_01
> <% end %>
> <%= layout.column do %>
> content02
> <% end %>
> <% end %>
> 
> 
> I get the following output.
> 
> <div>
>  content_01
>  <div class="column_1 ">content_01</div>
>  content02
>  <div class="column_2 ">
>    content_01
>    <div class="column_1 ">content_01</div>
>    content02
>  </div>
> </div>
> 
> 
> As you can see, the buffer in between the captures doesn''t seem to
be
> cleared in the separate block scopes. As I sort of expected how
> capture would work...
> 
> I guess I''m having the same issues as pointed out here
>
http://stackoverflow.com/questions/4352167/cant-suppress-output-in-nested-block-helper-in-rails-3
> 
> Any ideas on how to fix this?  Thanks
> 
> -- 
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> To post to this group, send email to
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> 
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