Ruby 为什么'；my instance变量是否指向Watir:：Browser实例？

我真的很困惑。我在自动化测试套件中使用下面的Ruby类：

class FlightSearchPage

  attr_accessor :page_title

  def initialize(browser, page)
    @browser      = browser
    @start_url    = page
  end

  def method_missing(sym, *args, &block)
    @browser.send sym, *args, &block
  end

  @page_title   = @browser.title

  #def page_title
  #  @browser.title
  #end

end

我将其子类化为：

class BrandFlightsPage < FlightSearchPage


    def initialize(browser, page, brand)
      super(browser, page)
      [...snip...]
    end
end

class BrandFlightsPage

当我实例化子类时，传入@browser，一个watir webdriver对象@browser.title抛出：

nil:NilClass（NoMethodError）的未定义方法“title”

但是，如果我在FlightSearchPage中取消对page_title方法的注释，它将按预期工作。我还尝试了构造函数中的变量赋值

我绕了一圈试图找到这个，但我就是看不到

这是stacktrace：

undefined method `title' for nil:NilClass (NoMethodError)
/Users/Dazzla/Dropbox/src/Projects/over_the_watir/pages/flight_search_page.rb:13:in `<class:FlightSearchPage>'
/Users/Dazzla/Dropbox/src/Projects/over_the_watir/pages/flight_search_page.rb:1:in `<top (required)>'
/usr/local/rvm/rubies/ruby-1.9.3-p0/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:55:in `require'
/usr/local/rvm/rubies/ruby-1.9.3-p0/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:55:in `require'
/Users/Dazzla/Dropbox/src/Projects/over_the_watir/pages/brand_flight_search_page.rb:1:in `<top (required)>'
/usr/local/rvm/rubies/ruby-1.9.3-p0/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:55:in `require'
/usr/local/rvm/rubies/ruby-1.9.3-p0/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:55:in `require'
/Users/Dazzla/Dropbox/src/Projects/over_the_watir/features/step_definitions/steps.rb:1:in `<top (required)>'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/rb_support/rb_language.rb:129:in `load'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/rb_support/rb_language.rb:129:in `load_code_file'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime/support_code.rb:171:in `load_file'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime/support_code.rb:83:in `block in load_files!'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime/support_code.rb:82:in `each'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime/support_code.rb:82:in `load_files!'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime.rb:175:in `load_step_definitions'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime.rb:40:in `run!'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/cli/main.rb:43:in `execute!'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/cli/main.rb:20:in `execute'
/usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/bin/cucumber:14:in `<top (required)>'
/usr/local/rvm/gems/ruby-1.9.3-p0/bin/cucumber:19:in `load'
/usr/local/rvm/gems/ruby-1.9.3-p0/bin/cucumber:19:in `<main>'

nil:NilClass（NoMethodError）的未定义方法“title” /Users/Dazzla/Dropbox/src/Projects/over\u the\u watir/pages/flight\u search\u page.rb:13:in`' /Users/Dazzla/Dropbox/src/Projects/over\u the\u watir/pages/flight\u search\u page.rb:1:in`' /usr/local/rvm/rubies/ruby-1.9.3-p0/lib/ruby/site\u ruby/1.9.1/rubygems/custom\u require.rb:55:in'require' /usr/local/rvm/rubies/ruby-1.9.3-p0/lib/ruby/site\u ruby/1.9.1/rubygems/custom\u require.rb:55:in'require' /用户/Dazzla/Dropbox/src/Projects/over\u the\u watir/pages/brand\u flight\u search\u page.rb:1:in`' /usr/local/rvm/rubies/ruby-1.9.3-p0/lib/ruby/site\u ruby/1.9.1/rubygems/custom\u require.rb:55:in'require' /usr/local/rvm/rubies/ruby-1.9.3-p0/lib/ruby/site\u ruby/1.9.1/rubygems/custom\u require.rb:55:in'require' /Users/Dazzla/Dropbox/src/Projects/over_the_watir/features/step_definitions/steps.rb:1:in`' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/rb_-support/rb_-language.rb:129:in'load' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/rb_-support/rb_-language.rb:129:在“加载代码文件”中 /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime/support_code.rb:171:in'load_file' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime/support_code.rb:83:in`block in load_files！' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime/support_code.rb:82:in'each' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime/support_code.rb:82:in'load_files！' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime.rb:175:在“加载步骤定义”中 /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/runtime.rb:40:in'run！' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/cli/main.rb:43:in'execute！' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/lib/cucumber/cli/main.rb:20:in'execute' /usr/local/rvm/gems/ruby-1.9.3-p0/gems/cucumber-1.2.1/bin/cucumber:14:in`' /usr/local/rvm/gems/ruby-1.9.3-p0/bin/cucumber:19:in'load' /usr/local/rvm/gems/ruby-1.9.3-p0/bin/cucumber:19:in`' 这是因为

 attr_accessor :page_title

已经创建了一个getter和一个setter

我会把这个

@page_title   = @browser.title

在初始化方法中

class FlightSearchPage

  attr_accessor :page_title

  def initialize(browser, page)
    @browser      = browser
    @page_title   = @browser.title
    @start_url    = page
  end

  def method_missing(sym, *args, &block)
    @browser.send sym, *args, &block
  end

end

或者（更好）删除属性访问器，只添加一个方法

   class FlightSearchPage

      def initialize(browser, page)
        @browser      = browser
        @start_url    = page
      end

      def method_missing(sym, *args, &block)
        @browser.send sym, *args, &block
      end

      def page_title
        return @browser.title unless @browser
        "browser not set, no title"
      end

    end

正在实例化浏览器：

该文件位于名为env.rb的文件中，该文件在每次测试之前运行：

Before do
  @browser = Watir::Browser.new
end

它是在cucumber's World当前实例的上下文中运行的

---

我不明白的是，除此之外，所有其他浏览器方法在使用访问器实现时都能正常工作。

谢谢-我现在实际上已经恢复使用方法，因为在调用@browser.title时，将赋值放在构造函数中会返回空字符串。是的，因此，最好的方法是二等舱。只需检查浏览器是否为零。我更新了这个例子。谢谢-你知道为什么调用Browser#title会产生一个空字符串吗？不知道，页面有标题吗？也许这是一个时间问题？是的，确实如此-正如我所说的，它在使用该方法时按预期工作，但在实现为attr_访问器或attr_读取器时却不能。