这是一个通用的方法，它允许您在指定的日期中添加/减去任何类型的单位(年/月/日/小时/秒等)。

使用Swift 2.2

func addUnitToDate(unitType: NSCalendarUnit, number: Int, date:NSDate) -> NSDate {

    return NSCalendar.currentCalendar().dateByAddingUnit(
        unitType,
        value: number,
        toDate: date,
        options: NSCalendarOptions(rawValue: 0))!

}

print( addUnitToDate(.Day, number: 1, date: NSDate()) ) // Adds 1 Day To Current Date
print( addUnitToDate(.Hour, number: 1, date: NSDate()) ) // Adds 1 Hour To Current Date
print( addUnitToDate(.Minute, number: 1, date: NSDate()) ) // Adds 1 Minute To Current Date

// NOTE: You can use negative values to get backward values too

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)

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)

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]);

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。

斯威夫特2.0

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