ruby Win32 注册表 : The system cannot find the file specified when looking for registry key that doesn't exist

Question

我正在编写一个 ruby​​ 函数以从给定的 DisplayName 获取 UninstallString。我的函数只有在我给它一个现有的 DisplayName 来查找时才能成功运行，当我给它一个不存在的东西时它会崩溃。我不确定在什么条件下检查哪个变量(无？空？)所以我可以向我的脚本抛出异常打印一条消息“未找到”而不是崩溃？

require 'win32/registry'

def get_uninstallstring(app_name)

  paths = [ "Software\\Microsoft\\Windows\\CurrentVersion\\Uninstall",
            "Software\\Wow6432Node\\Microsoft\\Windows\\CurrentVersion\\Uninstall",
            "Software\\Wow6464Node\\Microsoft\\Windows\\CurrentVersion\\Uninstall"  ]
  access_type = Win32::Registry::KEY_ALL_ACCESS

  paths.each do |path|         # This is line 9
    Win32::Registry::HKEY_LOCAL_MACHINE.open(path, access_type) do |reg|
      reg.each_key do |key|
        k = reg.open(key) 
        app = k['DisplayName'] rescue nil
        if app == app_name
          str = k['UninstallString'] rescue nil
          return str
        end
      end
    end
  end
  return false
end

puts get_uninstallstring("ABC")    # This is line 24

这是错误输出:

C:/ruby/1.9.1/win32/registry.rb:385:in `open': The system cannot find the file specified. (Win32::Registry::Error)
        from C:/heliopolis/opscode/chef/embedded/lib/ruby/1.9.1/win32/registry.rb:496:in `open'
        from test.rb:10:in `block in get_uninstallstring'
        from test.rb:9:in `each'
        from test.rb:9:in `get_uninstallstring'
        from test.rb:24:in `<main>'

Answer 1

所以我自己找到了解决办法。在我真正获得它的值之前，我不得不编写另一个函数来检查给定路径中是​​否存在该键。

def key_exists?(path)
  begin
    Win32::Registry::HKEY_LOCAL_MACHINE.open(path, ::Win32::Registry::KEY_READ)
    return true
  rescue
    return false
  end
end

这里是修改后的 get 函数:

  paths.each do |path| 
    if key_exists?(path)
      Win32::Registry::HKEY_LOCAL_MACHINE.open(path, access_type) do |reg|
        reg.each_key do |key|
          k = reg.open(key)
          app = k['DisplayName'] rescue nil
          if app == app_name
        return k['UninstallString'] rescue nil
          end
        end
      end
    else
      return false
    end
  end