November 21 2009
Cocoa Tip: Extend NSDate
Categories are a seemless way to extend existing Cocoa classes like NSDate. In my post on relative dates, I see if two timestamps land on the same day, by zeroing out the hour/minute/second components. Recently, while working on an iPhone app, I refactored it, converting it from a transformer into a category.
@implementation NSDate (Utilities)
- (NSDate *)dateAtMidnight {
// Initialize the calendar and flags.
NSCalendar *calendar = [NSCalendar currentCalendar];
unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit |
NSDayCalendarUnit | NSWeekdayCalendarUnit;
// Set date's hour/minute/second to zero.
NSDateComponents *comps = [calendar components:unitFlags fromDate:self];
[comps setHour:0];
[comps setMinute:0];
[comps setSecond:0];
return [calendar dateFromComponents:comps];
}
@end
