日期格式 转换

yyyy-MM-dd HH:mm:ss    

1 . HH 表示24小时制

2 .  hh 表示12 小时制

DD  是错误的写法,会出现day解析异常 ,要小写

  var startCompo : DateComponents {         let startCompo = dateFormatter.calendar.dateComponents(yearSet, from: startDate ?? Date.init(timeIntervalSince1970: 0))          return startCompo      }

 var endCompo : DateComponents {         let endCompo = dateFormatter.calendar.dateComponents(yearSet, from: endDate ?? Date.init())          return endCompo      }

   var dateFormatter: DateFormatter {          let dateFormatter = DateFormatter.init()              dateFormatter.dateFormat = formate          return dateFormatter      }

var formate = "yyyy-MM-dd HH:mm:ss"

 let yearSet = Set(arrayLiteral: Calendar.Component.year,Calendar.Component.month,Calendar.Component.day,Calendar.Component.hour,Calendar.Component.minute,Calendar.Component.second)

var component: DateComponents {         return dateFormatter.calendar.dateComponents(yearSet, from: startDate!, to: endDate!)      }