因为日期、时间格式化在项目里面用得比较多，所以一般封装成一个方法，放在utils文件夹了，所以我先建了一个utils文件夹，然后新建一个文件叫做tools.dart。

class Tools {   static formatTime(timeStamp, {format = '{y}-{m}-{d} {h}:{i}:{s}'}) {     if(timeStamp == null) return null;     if ('$timeStamp'.length == 10) {       timeStamp *= 1000;     }     DateTime date = DateTime.fromMillisecondsSinceEpoch(timeStamp);     var formatObj = {       'y': date.year,       'm': date.month,       'd': date.day,       'h': date.hour,       'i': date.minute,       's': date.second,       'a': date.weekday,     };     RegExp exp = RegExp("{(y|m|d|h|i|s|a)+}");     var timeStr = format.replaceAllMapped(exp, (Match match) {       var result = match.group(0); // {m}       var key = match.group(1); // m       var value = formatObj[key];       if (key == 'a') return ['一', '二', '三', '四', '五', '六', '日'][value! - 1];       var s = '$value';       if (result!.isNotEmpty && value! < 10) {         s = '0$value';       }       return s;     });     return timeStr;   }    static getWeek(timeStamp) {     if(timeStamp == null) return null;     String week = '';     if ('$timeStamp'.length == 10) {       timeStamp *= 1000;     }     DateTime date = DateTime.fromMillisecondsSinceEpoch(timeStamp);     if (date.weekday == 0) week = "星期日";     if (date.weekday == 1) week = "星期一";     if (date.weekday == 2) week = "星期二";     if (date.weekday == 3) week = "星期三";     if (date.weekday == 4) week = "星期四";     if (date.weekday == 5) week = "星期五";     if (date.weekday == 6) week = "星期六";     return week;   } }