如何在Cocoa中获取当前日期

Question

我正在开始为iPhone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,我正在努力创建一个倒计时,直到午夜.要获得小时,分钟和秒的数量,我执行以下操作(我在某处找到):

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,我使用的每个地方-dateWithCalendarFormat:timeZone:都会出现以下错误:

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？

此外,我注意到在不同的地方,在不同的时间,星号(*)位于NSDate* now变量之后或之前NSDate *now.这两者有什么区别,为什么你会使用一个与另一个？

Answer 1

您有iOS 4.2的问题吗？使用此代码:

NSDate *currDate = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
[dateFormatter setDateFormat:@"dd.MM.YY HH:mm:ss"];
NSString *dateString = [dateFormatter stringFromDate:currDate];
NSLog(@"%@",dateString);

- > 20.01.2011 10:36:02

Answer 2

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];

现在NSDate*和NSDate*之间没有区别,这只是一个偏好问题.从编译器的角度看,没有任何变化.

Answer 3

您还可以使用:

CFGregorianDate currentDate = CFAbsoluteTimeGetGregorianDate(CFAbsoluteTimeGetCurrent(), CFTimeZoneCopySystem());
countdownLabel.text = [NSString stringWithFormat:@"%02d:%02d:%02.0f", currentDate.hour, currentDate.minute, currentDate.second];
CFRelease(currentDate); // Don't forget this! VERY important

我认为这有以下优点:

2. 没有直接的内存分配.
3. 秒是双精度而不是整数.
4. 没有消息呼叫.
5. 快点.

Answer 4

//您可以使用以下代码获取当前日期/时间:

    NSDate* date = [NSDate date];
    NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
    NSTimeZone *destinationTimeZone = [NSTimeZone systemTimeZone];
    formatter.timeZone = destinationTimeZone;
    [formatter setDateStyle:NSDateFormatterLongStyle];
    [formatter setDateFormat:@"MM/dd/yyyy hh:mma"];
    NSString* dateString = [formatter stringFromDate:date];

Answer 5

替换这个:

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];

有了这个:

NSDate* now = [NSDate date];
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *dateComponents = [gregorian components:(NSHourCalendarUnit  | NSMinuteCalendarUnit | NSSecondCalendarUnit) fromDate:now];
NSInteger hour = [dateComponents hour];
NSInteger minute = [dateComponents minute];
NSInteger second = [dateComponents second];
[gregorian release];
countdownLabel.text = [NSString stringWithFormat:@"%02d:%02d:%02d", hour, minute, second];