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”。

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)

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?

swift 5更新

let nextDate = fromDate.addingTimeInterval(60*60*24)

NSDateComponents *dayComponent = [[[NSDateComponents alloc] init] autorelease];
dayComponent.day = 1;

NSCalendar *theCalendar = [NSCalendar currentCalendar];
dateToBeIncremented = [theCalendar dateByAddingComponents:dayComponent toDate:dateToBeIncremented options:0];

好吧，我以为这对我有用。但是，如果您使用它在2013年3月31日之后添加一天，它将返回一个只添加了23小时的日期。它实际上可能有24小时，但在计算中只添加了23:00小时。

类似地，如果您向前扩展到2013年10月28日，代码将增加25小时，从而导致日期时间为2013-10-28 01:00:00。

为了添加一天，我正在做的事情在顶部，添加:

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

复杂，主要是由于夏令时。

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)