NSDate类提供了创建date,比较date以及计算两个date之间间隔的功能。Date对象是不可改变的。
如果你要创建date对象并表示当前日期,你可以alloc一个NSDate对象并调用init初始化:
NSDate *now = [[NSDate alloc] init];
创建一定时间间隔的NSDate对象:
NSTimeInterval secondsPerDay = 24 * 60 * 60; NSDate *tomorrow = [[NSDate alloc] initWithTimeIntervalSinceNow:secondsPerDay]; NSDate *yesterday = [[NSDate alloc] initWithTimeIntervalSinceNow:-secondsPerDay]; [tomorrow release]; [yesterday release];
NSTimeInterval secondsPerDay = 24 * 60 * 60; NSDate *today = [[NSDate alloc] init]; NSDate *tomorrow, *yesterday; tomorrow = [today dateByAddingTimeInterval: secondsPerDay]; yesterday = [today dateByAddingTimeInterval: -secondsPerDay]; [today release];
if (fabs([date2 timeIntervalSinceDate:date1]) < 60) ...
日历对象封装了对系统日期的计算,包括这一年开始,总天数以及划分。你将使用日历对象对绝对日期与date components(包括年,月,日,时,分,秒)进行转换。
NSCalendar定义了不同的日历,包括佛教历,格里高利历等(这些都与系统提供的本地化设置相关)。NSCalendar与NSDateComponents对象紧密相关。
你可以通过NSCalendar对象的currentCalendar方法来获得当前系统用户设置的日历。
NSCalendar *currentCalendar = [NSCalendar currentCalendar]; NSCalendar *japaneseCalendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSJapaneseCalendar]; NSCalendar *usersCalendar = [[NSLocale currentLocale] objectForKey:NSLocaleCalendar];usersCalendar和currentCalendar对象是相等的,尽管他们是不同的对象。
你可以使用NSDateComponents对象来表示一个日期对象的组件——例如年,月,日和小时。如果要使一个NSDateComponents对象有意义,你必须将其与一个日历对象相关联。下面的代码示例了如何创建一个NSDateComponents对象:
NSDateComponents *components = [[NSDateComponents alloc] init]; [components setDay:6]; [components setMonth:5]; [components setYear:2004]; NSInteger weekday = [components weekday]; // Undefined (== NSUndefinedDateComponent)
NSDate *today = [NSDate date]; NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; NSDateComponents *weekdayComponents = [gregorian components:(NSDayCalendarUnit | NSWeekdayCalendarUnit) fromDate:today]; NSInteger day = [weekdayComponents day]; NSInteger weekday = [weekdayComponents weekday]; 同样你也可以从NSDateComponents对象来创建NSDate对象: NSDateComponents *components = [[NSDateComponents alloc] init]; [components setWeekday:2]; // Monday [components setWeekdayOrdinal:1]; // The first Monday in the month [components setMonth:5]; // May [components setYear:2008]; NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; NSDate *date = [gregorian dateFromComponents:components];
你也可以创建一个不带年份的NSDate对象,这样的操作系统会自动生成一个年份,但在后面的代码中不会使用其自动生成的年份。
NSDateComponents *components = [[NSDateComponents alloc] init]; [components setMonth:11]; [components setDay:7]; NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; NSDate *birthday = [gregorian dateFromComponents:components];
NSDateComponents *comps = [[NSDateComponents alloc] init]; [comps setDay:6]; [comps setMonth:5]; [comps setYear:2004]; NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; NSDate *date = [gregorian dateFromComponents:comps]; [comps release]; [gregorian release]; NSCalendar *hebrew = [[NSCalendar alloc] initWithCalendarIdentifier:NSHebrewCalendar]; NSUInteger unitFlags = NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit; NSDateComponents *components = [hebrew components:unitFlags fromDate:date]; NSInteger day = [components day]; // 15 NSInteger month = [components month]; // 9 NSInteger year = [components year]; // 5764
在当前时间加上一个半小时:
NSDate *today = [[NSDate alloc] init]; NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; NSDateComponents *offsetComponents = [[NSDateComponents alloc] init]; [offsetComponents setHour:1]; [offsetComponents setMinute:30]; // Calculate when, according to Tom Lehrer, World War III will end NSDate *endOfWorldWar3 = [gregorian dateByAddingComponents:offsetComponents toDate:today options:0];
NSDate *today = [[NSDate alloc] init]; NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; // Get the weekday component of the current date NSDateComponents *weekdayComponents = [gregorian components:NSWeekdayCalendarUnit fromDate:today]; /* Create a date components to represent the number of days to subtract from the current date. The weekday value for Sunday in the Gregorian calendar is 1, so subtract 1 from the number of days to subtract from the date in question. (If today is Sunday, subtract 0 days.) */ NSDateComponents *componentsToSubtract = [[NSDateComponents alloc] init]; [componentsToSubtract setDay: 0 - ([weekdayComponents weekday] - 1)]; NSDate *beginningOfWeek = [gregorian dateByAddingComponents:componentsToSubtract toDate:today options:0]; /* Optional step: beginningOfWeek now has the same hour, minute, and second as the original date (today). To normalize to midnight, extract the year, month, and day components and create a new date from those components. */ NSDateComponents *components = [gregorian components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit) fromDate: beginningOfWeek]; beginningOfWeek = [gregorian dateFromComponents:components];
如何可以计算出一周的第一天(根据系统的日历设置):
NSDate *today = [[NSDate alloc] init]; NSDate *beginningOfWeek = nil; BOOL ok = [gregorian rangeOfUnit:NSWeekCalendarUnit startDate:&beginningOfWeek interval:NULL forDate: today];
NSDate *startDate = ...; NSDate *endDate = ...; NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; NSUInteger unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit; NSDateComponents *components = [gregorian components:unitFlags fromDate:startDate toDate:endDate options:0]; NSInteger months = [components month]; NSInteger days = [components day];
使用Category来计算同一时代(AD|BC)两个日期午夜之间的天数:
@implementation NSCalendar (MySpecialCalculations) -(NSInteger)daysWithinEraFromDate:(NSDate *) startDate toDate:(NSDate *) endDate { NSInteger startDay=[self ordinalityOfUnit:NSDayCalendarUnit inUnit: NSEraCalendarUnit forDate:startDate]; NSInteger endDay=[self ordinalityOfUnit:NSDayCalendarUnit inUnit: NSEraCalendarUnit forDate:endDate]; return endDay-startDay; } @end
@implementation NSCalendar (MyOtherMethod) -(NSInteger) daysFromDate:(NSDate *) startDate toDate:(NSDate *) endDate { NSCalendarUnit units=NSEraCalendarUnit | NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit; NSDateComponents *comp1=[self components:units fromDate:startDate]; NSDateComponents *comp2=[self components:units fromDate endDate]; [comp1 setHour:12]; [comp2 setHour:12]; NSDate *date1=[self dateFromComponents: comp1]; NSDate *date2=[self dateFromComponents: comp2]; return [[self components:NSDayCalendarUnit fromDate:date1 toDate:date2 options:0] day]; } @end
-(BOOL)isDateThisWeek:(NSDate *)date { NSDate *start; NSTimeInterval extends; NSCalendar *cal=[NSCalendar autoupdatingCurrentCalendar]; NSDate *today=[NSDate date]; BOOL success= [cal rangeOfUnit:NSWeekCalendarUnit startDate:&start interval: &extends forDate:today]; if(!success) return NO; NSTimeInterval dateInSecs = [date timeIntervalSinceReferenceDate]; NSTimeInterval dayStartInSecs= [start timeIntervalSinceReferenceDate]; if(dateInSecs > dayStartInSecs && dateInSecs < (dayStartInSecs+extends)){ return YES; } else { return NO; } }