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)

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)

你可以使用NSDate的方法- (id)dateByAddingTimeInterval:(NSTimeInterval)秒，其中秒为60 * 60 * 24 = 86400

iOS 8+， OSX 10.9+， Objective-C

NSCalendar *cal = [NSCalendar currentCalendar];    
NSDate *tomorrow = [cal dateByAddingUnit:NSCalendarUnitDay 
                                   value:1 
                                  toDate:[NSDate date] 
                                 options:0];

使用以下代码:

NSDate *now = [NSDate date];
int daysToAdd = 1;
NSDate *newDate1 = [now dateByAddingTimeInterval:60*60*24*daysToAdd];

As

addTimeInterval

现在已弃用。

Swift 4.0(在这个精彩的答案中与Swift 3.0相同，只是为了让像我这样的新手清楚)

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