NSDate *now = [NSDate date];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit fromDate:now];
NSDate *startDate = [calendar dateFromComponents:components];
NSLog(@"StartDate = %@", startDate);

components.day += 1;
NSDate *endDate = [calendar dateFromComponents:components];
NSLog(@"EndDate = %@", endDate);

iOS 8+， OSX 10.9+， Objective-C

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

斯威夫特5

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

objective - c

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
// now build a NSDate object for the next day
NSDateComponents *offsetComponents = [[NSDateComponents alloc] init];
[offsetComponents setDay:1];
NSDate *nextDate = [gregorian dateByAddingComponents:offsetComponents toDate: [NSDate date] options:0];

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

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)

只是为了好玩，通过一些扩展和操作符重载，你可以得到一些不错的东西，比如:

let today = Date()
let tomorrow = today + 1.days

, or

var date = Date()
date += 1.months

下面是支持代码:

extension Calendar {
    struct ComponentWithValue {
        let component: Component
        let value: Int
    }
}

extension Int {
    var days: Calendar.ComponentWithValue {
        .init(component: .day, value: self)
    }
    
    var months: Calendar.ComponentWithValue {
        .init(component: .month, value: self)
    }
}

func +(_ date: Date, _ amount: Calendar.ComponentWithValue) -> Date {
    Calendar.current.date(byAdding: amount.component, value: amount.value, to: date)!
}

func +(_ amount: Calendar.ComponentWithValue, _ date: Date) -> Date {
    date + amount
}

func +=(_ date: inout Date, _ amount: Calendar.ComponentWithValue) {
    date = date + amount
}

代码是最少的，并且可以很容易地扩展到允许.月，.年，.小时等。还可以无缝添加对减法(-)的支持。

虽然在+操作符的实现中有一个强制的展开，但是不确定在哪种情况下日历可以返回nil日期。