ios - IOS中没有可见的@interface声明选择器 'ordinalityOfUnit:inUnit:forDate:'

Question

我尝试计算两个 NSDate 之间的天数我使用了这个 https://developer.apple.com/library/ios/#documentation/cocoa/Conceptual/DatesAndTimes/Articles/dtCalendricalCalculations.html

Listing 13 Days between two dates, as the number of midnights between

@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

这是我的代码:

@implementation MapViewController
-(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;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
}

@end

但是我遇到了这个错误。请帮助我!!

 No visible @interface for 'MapViewController' declares the selector 'ordinalityOfUnit:inUnit:forDate:'

Answer 1

像这样使用:

[[NSCalendar currentCalendar] ordinalityOfUnit:NSDayCalendarUnit
                                       inUnit: NSEraCalendarUnit forDate:startDate];