倒计时

//
[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerFireMethod:) userInfo:nil repeats:YES];

//

• (void)timerFireMethod:(NSTimer *)theTimer
  {
  BOOL timeStart = YES;
  NSCalendar *cal = [NSCalendar currentCalendar];//定义一个NSCalendar对象
  NSDateComponents *endTime = [[NSDateComponents alloc] init]; //初始化目标时间...
  NSDate *today = [NSDate date]; //得到当前时间

  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
  NSDate *dateString = [dateFormatter dateFromString:todate];
  NSString *overdate = [dateFormatter stringFromDate:dateString];
  // NSLog(@"overdate=%@",overdate);
  static int year;
  static int month;
  static int day;
  static int hour;
  static int minute;
  static int second;
  if(timeStart) {//从NSDate中取出年月日，时分秒，但是只能取一次
  year = [[overdate substringWithRange:NSMakeRange(0, 4)] intValue];
  month = [[overdate substringWithRange:NSMakeRange(5, 2)] intValue];
  day = [[overdate substringWithRange:NSMakeRange(8, 2)] intValue];
  hour = [[overdate substringWithRange:NSMakeRange(11, 2)] intValue];
  minute = [[overdate substringWithRange:NSMakeRange(14, 2)] intValue];
  second = [[overdate substringWithRange:NSMakeRange(17, 2)] intValue];
  timeStart= NO;
  }

  [endTime setYear:year];
  [endTime setMonth:month];
  [endTime setDay:day];
  [endTime setHour:hour];
  [endTime setMinute:minute];
  [endTime setSecond:second];
  NSDate *overTime = [cal dateFromComponents:endTime]; //把目标时间装载入date
  //用来得到具体的时差，是为了统一成北京时间
  unsigned int unitFlags = NSYearCalendarUnit| NSMonthCalendarUnit| NSDayCalendarUnit| NSHourCalendarUnit| NSMinuteCalendarUnit| NSSecondCalendarUnit;
  NSDateComponents *d = [cal components:unitFlags fromDate:today toDate:overTime options:0];
  NSString *t = [NSString stringWithFormat:@"%d", [d day]];
  NSString *h = [NSString stringWithFormat:@"%d", [d hour]];
  NSString *fen = [NSString stringWithFormat:@"%d", [d minute]];
  if([d minute] < 10) {
  fen = [NSString stringWithFormat:@"0%d",[d minute]];
  }
  NSString *miao = [NSString stringWithFormat:@"%d", [d second]];
  if([d second] < 10) {
  miao = [NSString stringWithFormat:@"0%d",[d second]];
  }
  // NSLog(@"===%@天 %@:%@:%@",t,h,fen,miao);
  [_longtime setText:[NSString stringWithFormat:@"%@天 %@:%@:%@",t,h,fen,miao]];
  if([d second] > 0) {
  //计时尚未结束，do_something
  // [_longtime setText:[NSString stringWithFormat:@"%@:%@:%@",d,fen,miao]];
  } else if([d second] == 0) {
  //计时结束 do_something

  } else{
  //计时器失效
  [theTimer invalidate];
  }

}