（OBJ C）將消息calendarIdentifier發送到NSCalendar的實例並接收null

Question

我試圖將消息calendarIdentifier發送到NSCalendar的實例。 這是我的代碼：

#import <Foundation/Foundation.h> 

int main(int argc, const char * argv[]) { 

//Create a date instance. 
NSDate *now = [NSDate date]; 
NSLog(@"This NSDate Object lives at %p", now); 
NSLog(@"The date now is %@",now); 

//Seconds from the date instance and 1970. 
NSTimeInterval seconds_since_1970 = [now timeIntervalSince1970]; 
NSLog(@"Seconds since 1970: %f", seconds_since_1970); 

//Future date from date instance. 
NSDate *later = [now dateByAddingTimeInterval:100000]; 
NSLog(@"The date after 100,000 seconds from %@ is : %@", now, later); 

//Create calender instance with user settings. 
NSCalendar *cal = [[NSCalendar alloc] init]; 
NSString *calenderIdentity = [cal calendarIdentifier]; 
NSLog(@"My calender is %@", calenderIdentity); 



return 0; 
} 

但是，由於某種原因，我得到這個在控制檯返回：

2015-01-08 19:12:26.651 TimeAfterTime[1325:40863] This NSDate Object lives at 0x10010fe70 
2015-01-08 19:12:26.656 TimeAfterTime[1325:40863] The date now is 2015-01-09 00:12:26 +0000 
2015-01-08 19:12:26.656 TimeAfterTime[1325:40863] Seconds since 1970: 1420762346.651615 
2015-01-08 19:12:26.656 TimeAfterTime[1325:40863] The date after 100,000 seconds 
from 2015-01-09 00:12:26 +0000 is : 2015-01-10 03:59:06 +0000 
2015-01-08 19:12:26.656 TimeAfterTime[1325:40863] My calender is (null) 
Program ended with exit code: 0 

爲什麼我收到空？我試着環顧四周，但似乎無法找到任何東西。

感謝，

Answer 1

你需要一個已知的日曆類型提供給initWithCalendarIdentifier:初始化。只提供任何字符串不起作用。已知類型爲：

NSGregorianCalendar 
NSBuddhistCalendar 
NSChineseCalendar 
NSHebrewCalendar 
NSIslamicCalendar 
NSIslamicCivilCalendar 
NSJapaneseCalendar 
NSRepublicOfChinaCalendar 
NSPersianCalendar 
NSIndianCalendar 
NSISO8601Calendar 

這將爲identifier:消息生成一個非空值。

我發現這些常數在NSLocale.h。