如何从当前日期倒计时到特定的NSDate？

Question

我希望从当前时间到特定日期倒计时,并在标签中显示该值.我查看了一些NSTimer教程,但我无法弄清楚如何将它们应用到我的情况中.

NSTimeInterval TimeInterval = [aString doubleValue]; 
NSDate* upperDate = [aDate dateByAddingTimeInterval:TimeInterval];
NSDate* Today = [NSDate date];

//cell.myLabel.text = here i should write a countdown.

对不起代码不足.我经常尝试写一些自己的代码,然后在这里提问,但这次我无法想象要写什么.

编辑 因此,PartiallyFinite的答案,我想我如何设置计时器.但因为我使用tableview,我无法实现MyTimerLabel的重复消息.这就是我刚刚做的:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"MyCell";
    MekanListesiViewCell *cell = (MyCell *)[tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    if (cell == nil)
    {
        NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"MyCell" owner:self options:nil];
        cell = [nib objectAtIndex:0];
    }


    aClass *aC = [myArray objectAtIndex:indexPath.row];
    NSTimeInterval TimeInterval = [aC.aTimeIntervalwithString doubleValue];
    NSDate* UpperDate = [aC.aNSDate dateByAddingTimeInterval:TimeInterval];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"YYYY-MM-dd"];
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSUInteger unitFlags = NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSHourCalendarUnit|NSMinuteCalendarUnit|NSSecondCalendarUnit;
    NSDateComponents *dateComponents = [calendar components:unitFlags fromDate:[NSDate date] toDate:UpperDate options:0];
    NSInteger days     = [dateComponents day];
    NSInteger months   = [dateComponents month];
    NSInteger years    = [dateComponents year];
    NSInteger hours    = [dateComponents hour];
    NSInteger minutes  = [dateComponents minute];
    NSInteger seconds  = [dateComponents second];
    NSString *countdownText = [NSString stringWithFormat:@"%d Days %d:%d:%d", days, hours, minutes, seconds];
    cell.countdownText= countdownText;
    [self performSelector:@selector(updateCoundown)]; // The delay is in seconds, make it whatever you want.


    return cell;
}
At myCellView.h
@interface MekanListesiViewCell : UITableViewCell
@property (nonatomic, weak) IBOutlet UILabel *MyTimerLabel;
@property(weak)NSString *countdownText;
at myCellView.m

-(void)updateCoundown{

       MyTimerLabel.text = countdownText;
    [self performSelector:@selector(updateCoundown) withObject:nil afterDelay:1];
}

我在MyTimerLabel中什么都没得到.

Answer 1

使用此答案中的代码(下面复制粘贴以获得示例的完整性)来获取倒计时期间的各个组成部分:

- (void)updateCountdown {
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"YYYY-MM-dd"];
    NSDate *startingDate = [dateFormatter dateFromString:@"2005-01-01"];
    NSDate *endingDate = [NSDate date];

    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSUInteger unitFlags = NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSHourCalendarUnit|NSMinuteCalendarUnit|NSSecondCalendarUnit;
    NSDateComponents *dateComponents = [calendar components:unitFlags fromDate:startingDate toDate:endingDate options:0];

    NSInteger days     = [dateComponents day];
    NSInteger months   = [dateComponents month];
    NSInteger years    = [dateComponents year];
    NSInteger hours    = [dateComponents hour];
    NSInteger minutes  = [dateComponents minute];
    NSInteger seconds  = [dateComponents second];

然后我们可以创建一个包含所有这些数字的字符串:

    NSString *countdownText = [NSString stringWithFormat:@"%d Years %d Months %d Days %d Hours %d Minutes %d Seconds", days, months, years, hours, minutes, seconds];
    cell.myLabel.text = countdownText;

然后,我们可以使用performSelector:withObject:afterDelay:在指定的延迟后再次调用此方法(请注意延迟以秒为单位):

    [self performSelector:@selector(updateCountdown) withObject:nil afterDelay:1];
}