尝试仅使用NSDate时间

Question

我正在努力寻找一种方法来使用NSDate仅用于时间目的.我试图做以下代码:

- (void)awakeFromInsert
{
    NSDateComponents *comps = [[NSDateComponents alloc] init];
    comps.minute = 45;
    comps.second = 0;

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    self.periodDuration = [calendar dateFromComponents:comps];
    NSLog(@"periodDuration: %@",self.periodDuration);

    comps = [[NSDateComponents alloc] init];
    comps.hour = 8;
    comps.minute = 0;
    self.firstPeriodStartTime = [calendar dateFromComponents:comps];
    NSLog(@"firstPeriodTime: %@",self.periodDuration);
}

但我得到的结果是:

periodDuration: 0001-12-31 22:24:04 +0000
firstPeriodTime: 0001-12-31 22:24:04 +0000

结果我期待:

periodDuration: 45:00
firstPeriodTime: 08:00

我究竟做错了什么？我怎样才能解决这个问题？谢谢.

Answer 1

日期日志会误导您,如果您只使用少量组件形成日期,则无法获得唯一标识日期和时间的正确日期实例.

如果您尝试使用此代码剪切,您可以发现,如果您只是将日期转换回字符串,它就像您期望的那样

NSDateComponents *comps = [[NSDateComponents alloc] init];
comps.minute = 45;
comps.second = 0;

NSCalendar *calendar = [NSCalendar currentCalendar];
NSDate *periodDate = [calendar dateFromComponents:comps];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"mm:ss"];
NSLog(@"periodDuration: %@",[dateFormatter stringFromDate:periodDate]);

comps = [[NSDateComponents alloc] init];
comps.hour = 8;
comps.minute = 0;
NSDate *firstPeriodDate = [calendar dateFromComponents:comps];
[dateFormatter setDateFormat:@"HH:mm"];
NSLog(@"firstPeriodTime: %@",[dateFormatter stringFromDate:firstPeriodDate]);

periodDuration:45:00

firstPeriodTime:08:00