从iOS 8开始，你可以使用NSCalendar.dateByAddingUnit

Swift 1.x中的示例:

let today = NSDate()
let tomorrow = NSCalendar.currentCalendar()
    .dateByAddingUnit(
         .CalendarUnitDay, 
         value: 1, 
         toDate: today, 
         options: NSCalendarOptions(0)
    )

斯威夫特2.0:

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

斯威夫特3.0:

let today = Date()
let tomorrow = Calendar.current.date(byAdding: .day, value: 1, to: today)

我也有同样的问题;使用NSDate扩展:

- (id)dateByAddingYears:(NSUInteger)years
                 months:(NSUInteger)months
                   days:(NSUInteger)days
                  hours:(NSUInteger)hours
                minutes:(NSUInteger)minutes
                seconds:(NSUInteger)seconds
{
    NSDateComponents * delta = [[[NSDateComponents alloc] init] autorelease];
    NSCalendar * gregorian = [[[NSCalendar alloc]
                               initWithCalendarIdentifier:NSCalendarIdentifierGregorian] autorelease];

    [delta setYear:years];
    [delta setMonth:months];
    [delta setDay:days];
    [delta setHour:hours];
    [delta setMinute:minutes];
    [delta setSecond:seconds];

    return [gregorian dateByAddingComponents:delta toDate:self options: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]);

斯威夫特4.0

extension Date {
    func add(_ unit: Calendar.Component, value: Int) -> Date? {
        return Calendar.current.date(byAdding: unit, value: value, to: self)
    }
}

使用

date.add(.day, 3)!   // adds 3 days
date.add(.day, -14)!   // subtracts 14 days

注意:如果你不知道为什么代码行以感叹号结尾，可以在谷歌上查找“Swift optional”。

基于highmaintenance的回答和vikingosegundo的评论，一个工作的Swift 3+实现。这个日期扩展也有额外的选项来改变年，月和时间:

extension Date {

    /// Returns a Date with the specified amount of components added to the one it is called with
    func add(years: Int = 0, months: Int = 0, days: Int = 0, hours: Int = 0, minutes: Int = 0, seconds: Int = 0) -> Date? {
        let components = DateComponents(year: years, month: months, day: days, hour: hours, minute: minutes, second: seconds)
        return Calendar.current.date(byAdding: components, to: self)
    }

    /// Returns a Date with the specified amount of components subtracted from the one it is called with
    func subtract(years: Int = 0, months: Int = 0, days: Int = 0, hours: Int = 0, minutes: Int = 0, seconds: Int = 0) -> Date? {
        return add(years: -years, months: -months, days: -days, hours: -hours, minutes: -minutes, seconds: -seconds)
    }

}

如果按照OP的要求只增加一天，则用法如下:

let today = Date() // date is then today for this example
let tomorrow = today.add(days: 1)

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)