filename method
生成文件名称,目前的文件名称是以日期的天命名的
Implementation
String filename() {
final datetime = DateTime.now();
String yearStr = datetime.year.toString().padLeft(4, "0");
String monthStr = datetime.month.toString().padLeft(2, "0");
String dayStr = datetime.day.toString().padLeft(2, "0");
return yearStr + '-' +monthStr + '-' + dayStr;
}