iOS特定日期倒计时计时器

Question

我正在尝试为特定日期设置倒计时计时器。我使用：

-(void) viewWillAppear:(BOOL)animated {
    NSString *str =@"12/27/2013";
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    [formatter setDateFormat:@"MM/dd/yyyy"];
    NSDate *date = [formatter dateFromString:str];
    NSTimeInterval numberOfSecondsUntilSelectedDate = [date timeIntervalSinceNow];
    NSInteger numberOfDays = numberOfSecondsUntilSelectedDate / 86400;

    startTime = [[NSDate date] retain];
    secondsLeft = numberOfDays;
    NSLog(@"number%f", numberOfSecondsUntilSelectedDate);
    [self countdownTimer];
}
- (void)updateCounter:(NSTimer *)theTimer {
    if(secondsLeft > 0 ){
        secondsLeft -- ;
        days = secondsLeft / 86400;
        NSLog(@"%d", days);
        hours = secondsLeft / 3600;
        minutes = (secondsLeft % 3600) / 60;
        seconds = (secondsLeft %3600) % 60;
        myCounterLabel.text = [NSString stringWithFormat:@"%02d Days %02d Hours %02d Minutes %02d Seconds", days, hours, minutes, seconds];
    }
    else{
        secondsLeft = 16925;
    }
}
-(void)countdownTimer{
    secondsLeft = hours = minutes = seconds = 0;
    if([timer isValid])
    {
        [timer release];
    }
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
    timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(updateCounter:) userInfo:nil repeats:YES];
    [pool release];
}

然而，这一天一直是0。我做错了什么？

Answer 1

倒计时到特定日期的方法是启动一个计时器，并在每次触发时询问该日期是否已经过去。第二个问题是如何计算UI的小时-分-秒。答案是NSDateFormatter——绝对不是*60或*24数学。

@property (strong, nonatomic) NSDate *targetDate;
// compute targetDate as you have it
// ...
self.targetDate = [formatter dateFromString:str]
// start a timer
[NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(updateCounter:) userInfo:nil repeats:YES]; 
- (void)updateCounter:(NSTimer *)theTimer {
    NSDate *now = [NSDate date]; 
    // has the target time passed?
    if ([self.targetDate earlierDate:now] == self.targetDate) {
        [theTimer invalidate];
    } else {
        NSUInteger flags = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
        NSDateComponents *components = [[NSCalendar currentCalendar] components:flags fromDate:now toDate:self.targetDate options:0];
        NSLog(@"there are %ld hours, %ld minutes and %ld seconds remaining", (long)[components hour], (long)[components minute], (long)[components second]);
    }
}

Answer 2

逻辑错误。。。。

-(void) viewWillAppear:(BOOL)animated {
    NSString *str =@"12/27/2013";
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    [formatter setDateFormat:@"MM/dd/yyyy"];
    NSDate *date = [formatter dateFromString:str];
    NSTimeInterval numberOfSecondsUntilSelectedDate = [date timeIntervalSinceNow];
    NSInteger numberOfDays = numberOfSecondsUntilSelectedDate / 86400;

    startTime = [[NSDate date] retain];
    secondsLeft = numberOfSecondsUntilSelectedDate;
    NSLog(@"number%f", numberOfSecondsUntilSelectedDate);
    [self countdownTimer];
}