问题描述
我正在开始为 iPhone 进行开发,因此我在网上查看不同的教程以及自己尝试一些不同的东西.目前,我正在尝试创建一个倒计时直到午夜.要获得小时数、分钟数和秒数,我执行以下操作(我在某处找到了):
I'm getting started developing for the iPhone and as such I am looking at different tutorials online as well as trying some different things out myself. Currently, I'm trying to create a countdown until midnight. To get the number of hour, minutes, and seconds, I do the following (which I found somewhere):
NSDate* now = [NSDate date];
int hour = 23 - [[now dateWithCalendarFormat:nil timeZone:nil] hourOfDay];
int min = 59 - [[now dateWithCalendarFormat:nil timeZone:nil] minuteOfHour];
int sec = 59 - [[now dateWithCalendarFormat:nil timeZone:nil] secondOfMinute];
countdownLabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hour, min,sec];
但是,我使用 -dateWithCalendarFormat:timeZone:
的每个地方都会出现以下错误:
However, each place I use -dateWithCalendarFormat:timeZone:
I get the following error:
warning: 'NSDate' may not respond to '-dateWithCalendarFormat:timeZone:'
(Messages without a matching method signature will be assumed to return 'id' and accept '...' as arguments.)
warning: no '-hourOfDay' method found
error: invalid operands to binary - (have 'int' and 'id')
这看起来很简单.我错过了什么?
This seems like something very simple. What am I missing?
另外,我在不同的地方和不同的时间注意到星号 (*) 位于 NSDate* now
之后或变量 NSDate *now.两者有什么区别,为什么要使用一个而不是另一个?
Also, I've noticed at different places and at different times the asterisk (*) is located either right after the time
NSDate* now
or right before the variable NSDate *now
. What is the difference in the two and why would you use one versus the other?
推荐答案
您必须使用以下内容:
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *dateComponents = [gregorian components:(NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit) fromDate:yourDateHere];
NSInteger hour = [dateComponents hour];
NSInteger minute = [dateComponents minute];
NSInteger second = [dateComponents second];
[gregorian release];
NSDate* now 和 NSDate *now 之间没有区别,只是喜好问题.从编译器的角度来看,没有任何变化.
There is no difference between NSDate* now and NSDate *now, it's just a matter of preference. From the compiler perspective, nothing changes.
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