I would like to subtract 4 hours from a date. I read the date string into an NSDate object use the following code:
NSDateFormatter * dateFormatter = [[[NSDat
NSDate *newDate = [theDate dateByAddingTimeInterval:-3600*4];
Link to documentation.
NSDate *newDate = [[[NSDate alloc] initWithTimeInterval:-3600*4
sinceDate:theDate]] autorelease];
Link to documentation.
dateFromString function returns NSDate, not NSString. you should change,
NSDate * theDate = [dateFormatter dateFromString:datetemp];
//in Swift 3
//subtract 3 hours
let calendar = NSCalendar.autoupdatingCurrent
newDate = calendar.date(byAdding:.hour, value: -3, to: originalDate)
Since iOS 8 there is the more convenient dateByAddingUnit
:
Swift 2.x
//subtract 3 hours
let calendar = NSCalendar.autoupdatingCurrentCalendar()
newDate = calendar.dateByAddingUnit(.Hour, value: -3, toDate: originalDate, options: [])
In Swift 4 :
var baseDate = ... // something
let dateMinus4Hours = Calendar.current.date(byAdding: .hour, value: -4, to: baseDate)
don't go with 24*3600
and stuff, that's asking for trouble.
Here a function which might be useful as it returns the date -4 h considering that this may also change the date and the month and eventually the year. the .searchBackward option is the important part :)
public static func correctSecondComponent(date: Date, calendar: Calendar = Calendar(identifier: Calendar.Identifier.gregorian))->Date {
let hour = calendar.component(.hour, from: date)
let e = (calendar as NSCalendar).date(byAdding: NSCalendar.Unit.hour, value: -4, to: date, options:.searchBackwards)!
return e
}