Problem combining a date and a time into a single NSDate

Question

I am trying to combine the time value (hours, minutes, seconds) of one NSDate with the date value (day, month, year) of a second NSDate with this method:

+ (NSDate *)combineDate:(NSDate *)date withTime:(NSDate *)time {

    NSCalendar *gregorian = [[NSCalendar alloc]
        initWithCalendarIdentifier:NSGregorianCalendar];

    NSDateComponents *dateComponents = [gregorian components:(NSDayCalendarUnit | 
        NSWeekdayCalendarUnit) fromDate:date];
    NSDateComponents *timeComponents = [gregorian components:(NSDayCalendarUnit | 
        NSWeekdayCalendarUnit) fromDate:time];

    NSDateComponents *comp = [NSDateComponents alloc];
    [comp setSecond:[timeComponents second]];
    [comp setHour:[timeComponents hour]];
    [comp setMinute:[timeComponents minute]];
    [comp setYear:[dateComponents year]];
    [comp setMonth:[dateComponents month]];
    [comp setDay:[dateComponents day]];

    NSDate *combDate = [gregorian dateFromComponents:comp]; 

    [gregorian release];
    [comp release];

    return combDate;
}

... but what it's returning is effectively gibberish (the year comes out as "1", for example). Anybody see what's wrong with this method?

Answer 1

I was using the wrong calendar components. Here's the corrected function (now for ARC):

+ (NSDate *)combineDate:(NSDate *)date withTime:(NSDate *)time {

    NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:
        NSGregorianCalendar];

    unsigned unitFlagsDate = NSYearCalendarUnit | NSMonthCalendarUnit 
        |  NSDayCalendarUnit;
    NSDateComponents *dateComponents = [gregorian components:unitFlagsDate 
        fromDate:date];
    unsigned unitFlagsTime = NSHourCalendarUnit | NSMinuteCalendarUnit 
        |  NSSecondCalendarUnit;
    NSDateComponents *timeComponents = [gregorian components:unitFlagsTime 
        fromDate:time];

    [dateComponents setSecond:[timeComponents second]];
    [dateComponents setHour:[timeComponents hour]];
    [dateComponents setMinute:[timeComponents minute]];

    NSDate *combDate = [gregorian dateFromComponents:dateComponents];   

    return combDate;
}

Answer 2

Swift 3 extension:

func combineDateAndTime(date: Date, time: Date) -> Date {

    let calendar = NSCalendar.current

    let dateComponents = calendar.dateComponents([.year, .month, .day], from: date)
    let timeComponents = calendar.dateComponents([.hour, .minute, .second], from: time)

    var components = DateComponents()
    components.year = dateComponents.year
    components.month = dateComponents.month
    components.day = dateComponents.day
    components.hour = timeComponents.hour
    components.minute = timeComponents.minute
    components.second = timeComponents.second

    return calendar.date(from: components)!
}