ios - 在标签中显示倒数计时器

Question

我想显示一个倒数计时器。我有开始日期和结束日期。我需要显示剩余时间

天：时：分：秒

我从这个站点得到了一些代码，但是当结束日期过去时它会显示负号。请任何人帮助我。

-(void) viewWillAppear:(BOOL)animated
{
    timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self     selector:@selector(updateCountdown) userInfo:nil repeats: YES];
}

-(void) updateCountdown 
{
    NSString *dateString = @"14-12-2012";
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

    [dateFormatter setDateFormat:@"dd-MM-yyyy"];
    NSDate *dateFromString = [[NSDate alloc] init];
    // voila!
    dateFromString = [dateFormatter dateFromString:dateString];

    NSDate *now = [NSDate date];
    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSDateComponents *componentsHours = [calendar components:NSHourCalendarUnit fromDate:now];
    NSDateComponents *componentMint = [calendar components:NSMinuteCalendarUnit fromDate:now];    
    NSDateComponents *componentSec = [calendar components:NSSecondCalendarUnit fromDate:now];        

    NSCalendar *gregorianCalendar = [[NSCalendar alloc]      initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *componentsDaysDiff = [gregorianCalendar components:NSDayCalendarUnit
                                                        fromDate:now
                                                          toDate:dateFromString
                                                         options:0];

    lblDaysSetting.text=[NSString stringWithFormat:@"%02d",componentsDaysDiff.day];
    lblHouresSetting.text=[NSString stringWithFormat:@"%02d",(24-componentsHours.hour)];    
    lblMinitSetting.text=[NSString stringWithFormat:@"%02d",(60-componentMint.minute)];  
    lblSecSetting.text=[NSString stringWithFormat:@"%02d",(60-componentSec.second)];  
}

Answer 1

使用以下代码查找两个日期之间的差异：

NSDate *lastDate = fromDate;
NSDate *todaysDate = [NSDate date];

NSCalendar *gregorian = [[NSCalendar alloc]
                         initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *comps = [gregorian components:NSDayCalendarUnit fromDate:lastDate  toDate:todaysDate options:0];
int days = [comps day];
int minute = [comps minute];
int hour = [comps hour];
int second = [comps second];

Answer 2

尝试这个：

if(componentsDayDiff.day < 0) { //DOUBLE CHECK THIS WITH NSLOG, I DON'T KNOW WHICH ONE WILL BE NEGATIVE, BUT ONE OF THEM WILL
    [timer invalidate]; //Stop the timer, it's not needed anymore
    //Not _technically_ needed, but a good thing to have, format as you see fit
    lblDaysSetting.text = @"0";
    lblHouresSetting.text = @"0";
    lblMinitSetting.text = @"0";
    lblSecSetting.text = @"0";
    //[self done] //call whatever method you want when the countdown is complete.
} else {
    lblDaysSetting.text=[NSString stringWithFormat:@"%02d",componentsDaysDiff.day];
    lblHouresSetting.text=[NSString stringWithFormat:@"%02d",(24-componentsHours.hour)];    
    lblMinitSetting.text=[NSString stringWithFormat:@"%02d",(60-componentMint.minute)];  
    lblSecSetting.text=[NSString stringWithFormat:@"%02d",(60-componentSec.second)];  
}