Swift 4，如果你真正需要的是24小时轮班(60*60*24秒)而不是“1个日历天”

未来: let dayAhead = Date(timeIntervalSinceNow: TimeInterval(86400.0))

过去: let dayAgo = Date(timeIntervalSinceNow: TimeInterval(-86400.0))

NSDate *now = [NSDate date];
int daysToAdd = 1;
NSDate *tomorrowDate = [now dateByAddingTimeInterval:60*60*24*daysToAdd];

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"EEEE, dd MMM yyyy"];
NSLog(@"%@", [dateFormatter stringFromDate:tomorrowDate]);

简单的Swift扩展昨天和明天从任何日期:

extension Date {
    
    var previousDay: Date {
        Calendar.current.date(byAdding: DateComponents(day:-1), to: self)!
    }
    
    var nextDay: Date {
        Calendar.current.date(byAdding: DateComponents(day:+1), to: self)!
    }
    
}

我在这里根据问题中的建议强制展开可选选项: 何时dateByAddingComponents:toDate:options返回nil?

它的工作原理!

NSCalendar *calendar = [NSCalendar currentCalendar];
NSCalendarUnit unit = NSCalendarUnitDay;
NSInteger value = 1;
NSDate *today = [NSDate date];
NSDate *tomorrow = [calendar dateByAddingUnit:unit value:value toDate:today options:NSCalendarMatchStrictly];

对于swift 2.2:

let today = NSDate()
let tomorrow = NSCalendar.currentCalendar().dateByAddingUnit(
        .Day,
        value: 1,
        toDate: today,
        options: NSCalendarOptions.MatchStrictly)

希望这能帮助到一些人!

字符串扩展:转换String_Date >日期

extension String{
  func DateConvert(oldFormat:String)->Date{ // format example: yyyy-MM-dd HH:mm:ss 
    let isoDate = self
    let dateFormatter = DateFormatter()
    dateFormatter.locale = Locale(identifier: "en_US_POSIX") // set locale to reliable US_POSIX
    dateFormatter.dateFormat = oldFormat
    return dateFormatter.date(from:isoDate)!
  }
}

日期扩展:转换日期>字符串

extension Date{
 func DateConvert(_ newFormat:String)-> String{
    let formatter = DateFormatter()
    formatter.dateFormat = newFormat
    return formatter.string(from: self)
 }
}

日期扩展:获取+/-日期

extension String{
  func next(day:Int)->Date{
    var dayComponent    = DateComponents()
    dayComponent.day    = day
    let theCalendar     = Calendar.current
    let nextDate        = theCalendar.date(byAdding: dayComponent, to: Date())
    return nextDate!
  }

 func past(day:Int)->Date{
    var pastCount = day
    if(pastCount>0){
        pastCount = day * -1
    }
    var dayComponent    = DateComponents()
    dayComponent.day    = pastCount
    let theCalendar     = Calendar.current
    let nextDate        = theCalendar.date(byAdding: dayComponent, to: Date())
    return nextDate!
 }
}

用法:

let today = Date()
let todayString = "2020-02-02 23:00:00"
let newDate = today.DateConvert("yyyy-MM-dd HH:mm:ss") //2020-02-02 23:00:00
let newToday = todayString.DateConvert(oldFormat: "yyyy-MM-dd HH:mm:ss")//2020-02-02
let newDatePlus = today.next(day: 1)//2020-02-03 23:00:00
let newDateMinus = today.past(day: 1)//2020-02-01 23:00:00

参考:来自多重问题 我如何添加1天到一个NSDate? 数学函数转换正整数为负和负到正? 将NSString转换为NSDate(然后再转换回来)