customized_erro_form_builder.rb

require 'hpricot'

class CustomizedErrorFormBuilder < ActionView::Helpers::FormBuilder

  def label(method, text = nil, options = {})
    text = text || method.to_s.humanize
    object = @template.instance_variable_get("@#{@object_name}")

    unless object.nil? || options[:hide_errors]
      errors = object.errors.on(method.to_sym)
      if errors
        text += " <font class=\"error\">#{errors.is_a?(Array) ? errors.first : errors}</font>"
      end
    end
    text += " #{options[:additional_text]}" if options[:additional_text]
    html_tag = super(method, text, options)
    process_field(html_tag)
  end

  def text_field(method, options = {})
    object = @template.instance_variable_get("@#{@object_name}")
    error_class = 'fieldWithErrors'

    unless object.nil? || options[:hide_errors]
      errors = object.errors.on(method.to_sym)
      options[:class] = error_class if errors
    end

    text += " #{options[:additional_text]}" if options[:additional_text]

    html_tag = super(method, options)
    process_field(html_tag)
  end

  private
    def process_field(html_tag)
      html = Hpricot(html_tag)
      inner_html = html.search("//div").inner_html
      (inner_html.nil? or inner_html.strip.length == 0)? html_tag : inner_html
    end
end