将hh：mm：ss格式的NSString转换为NSDate以进行定时器倒计时

Question

我必须为特定间隔运行倒计时器，但如何在此功能中提供self.startDate

- (void)updateCounter:(NSTimer *)theTimer {

    NSDate *now = [NSDate date];
    // has the target time passed?
    if ([self.startDate earlierDate:now] == self.startDate) {
        [theTimer invalidate];
    } else {
        NSUInteger flags = NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
        NSDateComponents *components = [[NSCalendar currentCalendar] components:flags fromDate:now toDate:self.startDate options:0];

        NSLog(@"there are %d hours, %d minutes and %d seconds remaining", [components hour], [components minute], [components second]);
    }
}

Answer 1

使用以下方法将NSString转换为NSDate：

  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  [dateFormatter setDateFormat:@"HH:mm:ss"];
  NSDate *date = [dateFormatter dateFromString:yourString];