我完全被这个问题难住了。
我有以下代码:
puts block.at_xpath("*/img")["width"].to_i
width = block.at_xpath("*/img")["width"].to_i
我得到这个错误:
NokogiriTUT.rb:70:in `blockProcessor': undefined method `[]' for nil:NilClass (NoMethodError)
当我在这里输入put时它会返回期望的值
更新:
def blockProcessor(block)
header = block.xpath('td[@class="default"]/*/span[@class="comhead"]')
array = header.text.split
if array[0] != nil #checks to make sure we aren't at the top of the parent list
### Date and Time ###
if array[2] == 'hours' || array[2] == 'minutes'
date = Time.now
else
days = (array[1].to_i * 24 * 60 * 60)
date = Time.now - days
end
##Get Comment##
comment = block.at_xpath('*/span[@class="comment"]')
hash = comment.text.hash
#puts hash
##Manage Parent Here##
width = block.at_xpath("*/img")["width"].to_i
prevlevel = @parent_array[@parent_array.length-1][1]
if width == 0 #has parents
parentURL = header.xpath('a[@href][3]').to_s
parentURL = parentURL[17..23]
parentURL = "http://news.ycombinator.com/item?id=#{parentURL}"
parentdoc = Nokogiri::HTML(open(parentURL))
a = parentdoc.at_xpath("//html/body/center/table/tr[3]/td/table/tr")
nodeparent = blockProcessor(a)
@parent_array = []
node = [hash, width, nodeparent] #id, level, parent
@parent_array.push node
elsif width > prevlevel
nodeparent = @parent_array[@parent_array.length-1][0]
node = [hash, width, nodeparent]
@parent_array.push node
elsif width == prevlevel
nodeparent = @parent_array[@parent_array.length-1][2]
node = [hash, width, nodeparent]
@parent_array.push node
elsif width < prevlevel
until prevlevel == w do
@parent_array.pop
prevlevel = @parent_array[@parent_array.length-1][1]
end
nodeparent = @parent_array[@parent_array.length-1][2]
node = [hash, width, nodeparent]
@parent_array.push node
end
puts "Author: #{array[0]} with hash #{hash} with parent: #{nodeparent}"
##Handles Any Parents of Existing Comments ##
return hash
end
end
end
这是它所作用的块
<tr>
<td><img src="http://ycombinator.com/images/s.gif" height="1" width="0"></td>
<td valign="top"><center>
<a id="up_3004849" href="vote?for=3004849&dir=up&whence=%2f%78%3f%66%6e%69%64%3d%34%6b%56%68%71%6f%52%4d%38%44"><img src="http://ycombinator.com/images/grayarrow.gif" border="0" vspace="3" hspace="2"></a><span id="down_3004849"></span>
</center></td>
<td class="default">
<div style="margin-top:2px; margin-bottom:-10px; "><span class="comhead"><a href="user?id=patio11">patio11</a> 12 days ago | <a href="item?id=3004849">link</a> | <a href="item?id=3004793">parent</a> | on: <a href="item?id=3004471">Ask HN: What % of your job interviewees pass FizzB...</a></span></div>
<br><span class="comment"><font color="#000000">Every time FizzBuzz problems come up among engineers, people race to solve them and post their answers, then compete to see who can write increasingly more nifty answers for a question which does not seek niftiness at all.<p>I'm all for intellectual gamesmanship, but these are our professional equivalent of a doctor being asked to identify the difference between blood and water. You can do it. <i>We know</i>. Demonstrating that you can do it is not the point of the exercise. We do it to have a cheap-to-administer test to exclude people-who-cannot-actually-program-despite-previous-job-titles from the expensive portions of the hiring process.</p></font></span><p><font size="1"><u><a href="reply?id=3004849&whence=%2f%78%3f%66%6e%69%64%3d%34%6b%56%68%71%6f%52%4d%38%44">reply</a></u></font></p>
</td>
</tr>
您的基本问题是不理解XPath。(你在那里有很多同伴;XPath非常令人困惑。)你的选择器根本不匹配你认为它们匹配的东西。特别是那个爆炸的
*/img
//img
之类的
现在，因为 xpath选择器不匹配任何东西，这个Ruby语句的值
block.at_xpath("*/img")
是零。nil不支持[]，所以当你尝试调用["width"]时，Ruby会报错undefined method [] for nil:NilClass。
至于为什么只有当你把它赋值给一个变量时它才会爆炸……是啊，事实并非如此。你可能还改变了别的东西。
现在，请允许我做一些其他建设性的代码批评:
你的问题显然是故意让人难以回答的。在将来，请隔离有问题的代码，不要只是粘贴你的整个家庭作业(或这个屏幕刮板的任何用途)。
如果你把它做成一个可运行的Ruby文件，我们可以在我们的计算机上逐字执行，那就太好了，例如:
.
require "nokogiri"
doc = Nokogiri.parse <<-HTML
<tr>
<td><img src="http://ycombinator.com/images/s.gif" height="1" width="0"></td>
<td valign="top"><center>
<a id="up_3004849" href="vote?for=3004849&dir=up&whence=%2f%78%3f%66%6e%69%64%3d%34%6b%56%68%71%6f%52%4d%38%44"><img src="http://ycombinator.com/images/grayarrow.gif" border="0" vspace="3" hspace="2"></a><span id="down_3004849"></span>
</center></td>
<td class="default">
<div style="margin-top:2px; margin-bottom:-10px; ">
<span class="comhead">
<a href="user?id=patio11">patio11</a> 12 days ago | <a href="item?id=3004849">link</a> | <a href="item?id=3004793">parent</a> | on: <a href="item?id=3004471">Ask HN: What % of your job interviewees pass FizzB...</a>
</span>
</div>
<br><span class="comment"><font color="#000000">Every time FizzBuzz problems come up among engineers, people race to solve them and post their answers, then compete to see who can write increasingly more nifty answers for a question which does not seek niftiness at all.<p>I'm all for intellectual gamesmanship, but these are our professional equivalent of a doctor being asked to identify the difference between blood and water. You can do it. <i>We know</i>. Demonstrating that you can do it is not the point of the exercise. We do it to have a cheap-to-administer test to exclude people-who-cannot-actually-program-despite-previous-job-titles from the expensive portions of the hiring process.</p></font></span><p><font size="1"><u><a href="reply?id=3004849&whence=%2f%78%3f%66%6e%69%64%3d%34%6b%56%68%71%6f%52%4d%38%44">reply</a></u></font></p>
</td>
</tr>
HTML
width = doc.at_xpath("*/img")["width"].to_i
这样我们就可以用我们的电脑来调试，而不仅仅是用我们的大脑。
你现在写的是Ruby，而不是Java，所以要遵守Ruby的间距和命名约定:文件名是snake_case，缩进是2个空格，没有制表符，等等。阅读格式错误的代码确实很困难——这里的"错误"意味着"非标准"。"
任何地方你有一个描述性的注释(
### Date and Time ###)是一个机会来提取一个方法(def date_and_time(array))，使你的代码更干净，更容易调试。