时间运算之Calendars
Creating a Calendar1：You create a calendar object by specifying an identifier for the calendar you want. Mac OS X provides data for several different calendars—Buddhist, Chinese, Gregorian, Hebrew, Islamic, and Japanese—specified by constants in NSLocale.
NSCalendar *japaneseCalendar = [ initWithCalendarIdentifier:NSJapaneseCalendar];
2：You can get the calendar for the user's preferred locale (or in general from any NSLocale object) using the key NSLocaleCalendar,
NSCalendar *usersCalendar = [ initWithCalendarIdentifier: [ objectForKey:NSLocaleCalendar]];
3：or most easily using the NSCalendar method currentCalendar.
NSCalendar *currentCalendar = ;
Calendrical Calculations
取得时间差
NSDate *startDate = ...;NSDate *endDate = ...; NSCalendar *gregorian = [ initWithCalendarIdentifier:NSGregorianCalendar]; unsigned int unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit; NSDateComponents *components = ;int months = ;int days = ;
api：
1：从NSDate 中取得NSDateComponents 对象
Returns a NSDateComponents object containing a given date decomposed into specified components.
- (NSDateComponents *)components:(NSUInteger)unitFlags fromDate:(NSDate *)date
unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit |NSDayCalendarUnit;NSDate *date = ;NSDateComponents *comps = ;
2：取得时间差
Returns, as an NSDateComponents object using specified components, the difference between two supplied dates.
- (NSDateComponents *)components:(NSUInteger)unitFlags fromDate:(NSDate *)startingDate toDate:(NSDate *)resultDate options:(NSUInteger)opts
NSDate *startDate = ...;NSDate *endDate = ...;unsigned int unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit;NSDateComponents *comps = ;int months = ;int days = ;
3：在给定的NSDate 上增加几天，几年等。。。。
Returns a new NSDate object representing the absolute time calculated by adding given components to a given date.
- (NSDate *)dateByAddingComponents:(NSDateComponents *)comps toDate:(NSDate *)date options:(NSUInteger)opts
NSDate *currentDate = ;NSDateComponents *comps = [ init];;;NSDate *date = ;;
4：取得一个指定的时间
Returns a new NSDate object representing the absolute time calculated from given components.
- (NSDate *)dateFromComponents:(NSDateComponents *)comps
NSDateComponents *comps = [ init];;;;;;;NSDate *date = ;;
Calendar Units
Specify calendrical units such as day and month.
enum {
NSEraCalendarUnit = kCFCalendarUnitEra,
NSYearCalendarUnit = kCFCalendarUnitYear,
NSMonthCalendarUnit = kCFCalendarUnitMonth,
NSDayCalendarUnit = kCFCalendarUnitDay,
NSHourCalendarUnit = kCFCalendarUnitHour,
NSMinuteCalendarUnit = kCFCalendarUnitMinute,
NSSecondCalendarUnit = kCFCalendarUnitSecond,
NSWeekCalendarUnit = kCFCalendarUnitWeek,
NSWeekdayCalendarUnit = kCFCalendarUnitWeekday,
NSWeekdayOrdinalCalendarUnit = kCFCalendarUnitWeekdayOrdinal
};
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