从NSDate减去分钟

NSDate *today = [[NSDate alloc] init];
NSLog(@"%@", today);
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *offsetComponents = [[NSDateComponents alloc] init];
[offsetComponents setMinute:-10]; // note that I'm setting it to -1
NSDate *endOfWorldWar3 = [gregorian dateByAddingComponents:offsetComponents toDate:today options:0];
NSLog(@"%@", endOfWorldWar3);

// gives new date object with time 15 minutes earlier
NSDate *newDate = [oldDate dateByAddingTimeInterval:-60*15]; 

dateByAddingUnit

//subtract 15 minutes
let calendar = NSCalendar.autoupdatingCurrentCalendar()
newDate = calendar.dateByAddingUnit(.CalendarUnitMinute, value: -15, toDate: originalDate, options: nil)

let originalDate = NSDate() // "Jun 8, 2016, 12:05 AM"
let calendar = NSCalendar.currentCalendar()
let newDate = calendar.dateByAddingUnit(.Minute, value: -15, toDate: originalDate, options: []) // "Jun 7, 2016, 11:50 PM"

NSCalendarUnit

OptionSetType

.Minute

options

nil

Date

Calendar

let originalDate = Date() // "Jun 13, 2016, 1:23 PM"
let calendar = Calendar.current
let newDate = calendar.date(byAdding: .minute, value: -5, to: originalDate, options: []) // "Jun 13, 2016, 1:18 PM"

let newDate = calendar.date(byAdding: .minute, value: -5, to: originalDate) // "Jun 13, 2016, 1:18 PM"