Question

我正在尝试使用libxml的SAX解析器（如illustrated here），但我遇到了未定义的方法错误。

我的代码是

$domain_topics = Hash.new { |h,d| h[d] = [] }
parser = LibXML::XML::SaxParser.io(
  File.open("content.rdf.u8", "r:UTF-8")
)
class Callbacks
  include LibXML::XML::SaxParser::Callbacks
  def initialize
    @state = :top
    @topics = nil
  end
  def on_start_element(element, attributes)
    case @state
    when :top
      return unless element == 'ExternalPage'
      @state = :ExternalPage

      domain = attributes['about'].sub(%r!^\w+://([^"/]*)(?:/[^"]*)?$!, '\1')
      @topics = $domain_topics[domain]
    when :ExternalPage
      return unless element == 'topic'
      @state  = :topic
    end
  end
  def on_characters(characters)
    if @state == :topic and @topics
      @topics << characters
    end
  end
  def on_end_element(element)
    case @state
    when :ExternalPage
      @state = :top
      @topics = nil
    when :topic
      @state = :ExternalPage
    end
  end
end
parser.callbacks = Callbacks
parser.parse

当我运行它时：

% ./my_awesome_code.rb
./my_awesome_code.rb:1337:in `parse': undefined method `on_start_document' for Callbacks:Class (NoMethodError)

我在这里做错了什么？不应include LibXML::XML::SaxParser::Callbacks给出默认定义 on_start_document？

irb似乎证实了我的直觉：

 1.9.3p194 :009 > Callbacks.instance_methods.include? :on_start_document
 => true

Answer 1

我很愚蠢，并且错过了#callbacks=需要通过正确的回调传递实例，而不是类。所以我需要做的就是做

parser.callbacks = Callbacks.new

使用libxml的sax解析器时未定义的方法错误

1 个答案: