ios - 如何在小时和分钟上倒数计时器并在它为 0 时停止， objective-c

Question

  viewdidload

 {   
    NSDateFormatter *df = [[[NSDateFormatter alloc] init] init];
    [df setDateFormat:@"HH:mm:ss"];

    ctime=([df stringFromDate:[NSDate date]]);
    NSDate *date1 = [df dateFromString:@"12:44"];`
    NSDate *date2 = [df dateFromString:@"20:50"];
    NSTimeInterval interval = [date2 timeIntervalSinceDate:date1];
    int hours = (int)interval / 3600;             // integer division to get the hours part
    int minutes = (interval - (hours*3600)) / 60; // interval minus hours part (in seconds) divided by 60 yields minutes
    NSString *timeDiff = [NSString stringWithFormat:@"%d:%02d", hours, minutes];
    currHour=hours;
    currMinute=minutes;
    currSeconds=00;
    [self start];
}

-(void)start
{
    self.timer=[NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timerFired) userInfo:nil repeats:YES];

}
-(void)timerFired
{
    if((currHour>0 || currMinute>0 || currSeconds>=0) && currMinute>=0)
    {
        if(currSeconds==0)
        {

            currMinute-=1;
            currSeconds=59;
        }
        else if(currSeconds>0)
        {

            currSeconds-=1;
        }
        if(currMinute>-1)


enter code here
            [self.timeonelabel setText:[NSString stringWithFormat:@"%d%@%d%@",currHour,@":",currMinute,@":"]];
        //[self.hourlabel setText:[NSString stringWithFormat:@"%d%@",currHour,@":"]];
          //  [self.timeonelabel setText:[NSString stringWithFormat:@"%d%@%d%@",00,@":",currMinute,@":"]];
        [self.timetwolabel setText:[NSString stringWithFormat:@"%02d",currSeconds]];
    }
    else
    {
        [self.timer invalidate];
    }
}

在经过当前时间和结束时间后，计时器应该倒计时到 0。问题是计时器没有运行倒计时，请帮忙。我什至无法在 tableview 中显示计时器倒计时。请帮忙

Answer 1

关于从字符串创建日期，您的代码中有几处错误。首先，您在 NSDateFormatter 中指定的日期格式与您使用的实际格式不匹配 - 一个有秒，另一个没有。这意味着 dateFromString 将返回 nil。此外，您还应该指定一个日期，而不仅仅是时间，否则您无法确定您会得到今天的日期。

最后，您通过在原始变量中提取和跟踪 NSDate 的所有组件，使事情变得过于复杂。我宁愿做这样的事情:

- (void)viewDidLoad {
    [super viewDidLoad];

    NSDateFormatter *df = [[NSDateFormatter alloc] init];
    [df setDateFormat:@"YYYY/MM/dd HH:mm"];
    self.endTime = [df dateFromString:@"2016/02/23 11:00"];

    self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timerFired) userInfo:nil repeats:YES];
}

-(void)timerFired {
    if ([[NSDate date] compare:self.endTime] == NSOrderedAscending) {
        NSLog(@"still going");
        // enter code here
        // Use NSDateComponentsFormatter to show what you need to show
    }
    else {
        NSLog(@"done");
        [self.timer invalidate];
    }
}