NSDateComponents to NSDate - Swift

问题

I have this function :

private func getCurrentDateComponent() -> NSDateComponents {
        let date = NSDate()
        let calendar = NSCalendar.currentCalendar()
        let components = calendar.components(.CalendarUnitHour | .CalendarUnitMinute | .CalendarUnitMonth | .CalendarUnitYear | .CalendarUnitDay, fromDate: date)
        return components
    }

When I call it and I use the function date

var d = this.getCurrentDateComponent().date

I don't know why the variable d is nil...

Thank you for your help

Ysee

回答1:

That's how I do it:

let allUnits = NSCalendarUnit(rawValue: UInt.max)
return UICalendar.currentCalendar().components(allUnits, fromDate: NSDate())

Note that in Swift 2.0 the bitwise OR operator | is not used any more, instead the NSCalendarUnit conforms to the OptionSetType format:

let timeUnits : NSCalendarUnit = [.Hour, .Minute, .Second]

回答2:

Swift 4 :

let date = NSCalendar.current.date(from: components) 

// components is your component name

回答3:

You need to set the calendar before using NSDateComponents, because without calendar there in no date.

let components = calendar.components(.CalendarUnitHour | .CalendarUnitMinute | .CalendarUnitMonth | .CalendarUnitYear | .CalendarUnitDay, fromDate: date)
components.calendar = NSCalendar.currentCalendar();
return components

回答4:

The conversion between a date and date components always requires a calendar. You have two options (compare NSCalendar dateFromComponents: vs NSDateComponents date):

• Assign a calendar to the date components, i.e. add

  components.calendar = calendar
  

  to your getCurrentDateComponent() method. Then

  var d = getCurrentDateComponent().date
  

  works as expected. (Without assigning a calendar to the date components, the date property returns nil, as you observed.)

• Alternatively, call a calendar method for the conversion:

  let d = NSCalendar.currentCalendar().dateFromComponents(getCurrentDateComponent())
  

来源：https://stackoverflow.com/questions/31287638/nsdatecomponents-to-nsdate-swift