ios - 尝试仅将 NSDate 用于时间

Question

我正在努力寻找一种仅将 NSDate 用于时间用途的方法。我正在尝试执行以下代码:

- (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

我期待的结果:

periodDuration: 45:00
firstPeriodTime: 08:00

我做错了什么？我怎样才能解决这个问题？谢谢。

Answer 1

日期日志会误导您，如果您只使用少数几个组成部分组成日期，您将无法获得唯一标识日期和时间的正确日期实例。

如果您尝试截取这段代码，您会发现，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