iOS：使用按钮动态向前移动 NSDate

Question

我为我的日期创建了一个自定义类，需要通过按钮向前和向后移动日期。这是我显示今天日期的代码：

- (NSString *) showToday {

    NSCalendar *myCal = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];    
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

    [dateFormatter setCalendar:myCal];

    offsetComponents = [[NSDateComponents alloc] init];
//shows today 
    [offsetComponents setDay:0];

    NSDate *nextDate = [myCal dateByAddingComponents:offsetComponents toDate:[NSDate date] options:0];

    [dateFormatter setDateFormat:@"d"];
    NSString *currDay = [dateFormatter stringFromDate:nextDate];

    [NSString stringWithFormat:@"%@",currDay];

    [myCal release];
    [dateFormatter release];
    return currDay;
}

在我的 viewController 上：

customClass = [[customClass alloc]init];

    day.text = [cal showToday];

所以如果我需要提前一个日期，我只需将此行代码更改为：

//show tomorrow 
[offsetComponents setDay:1];

那么如何通过按钮动态更改此行并更改日期？

Answer 1

您可以为您的offsetComponents 变量声明int。然后：

- (IBAction)moveDatesForward:(id)sender {

    NSCalendar *persCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSPersianCalendar];    
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    NSLocale *IRLocal = [[NSLocale alloc] initWithLocaleIdentifier:@"fa_IR"];
    [dateFormatter setLocale:IRLocal];
    [dateFormatter setCalendar:persCalendar];

    offsetComponents = [[NSDateComponents alloc] init];

    offsetComponents.day = _dayNumber;

    NSDate *nextDate = [persCalendar dateByAddingComponents:offsetComponents toDate:[NSDate date] options:0];

    [dateFormatter setDateFormat:@"d"];
    dayLabel.text = [dateFormatter stringFromDate:nextDate];

    [NSString stringWithFormat:@"%@",dayLabel];

    [persCalendar release];
    [dateFormatter release];

      _dayNumber ++;

}

Answer 2

做这样的事情怎么样：

（使用 ARC - 不要抱怨内存泄漏。）

- (void) refreshDateLabel
{
    NSDateFormatter* dateFormatter = [NSDateFormatter new];
    [dateFormatter setTimeStyle:NSDateFormatterNoStyle];
    [dateFormatter setDateStyle:NSDateFormatterMediumStyle];

    self.dateLabel.text = [dateFormatter stringFromDate: self.date];
}

- (IBAction)forward:(id)sender
{
    self.date = [self.date dateByAddingTimeInterval: 24 * 60 * 60];
    [self refreshDateLabel];
}

- (IBAction)back:(id)sender
{
    self.date = [self.date dateByAddingTimeInterval: -(24 * 60 * 60)];
    [self refreshDateLabel];
}

在https://github.com/st3fan/StackOverflowAnswers/blob/master/DateSelection完成项目