    def zip_to_csv(zip_file)
      csv = nil
      @visualizer.unzip_status do
        # Use Zip::File for rubyzip >= 1.0.0, Zip::ZipFile for older.
        klass = defined?(Zip::File) ? Zip::File : Zip::ZipFile
        klass.foreach(zip_file) do |entry|
          File.extname(entry.name).downcase == '.csv' or next
          csv = CSV.parse(entry.get_input_stream.read.encode("utf-8", "sjis"))
          break
        end
      end
      csv
    end