これらの日付比較が多数ある場合、calendar:components:fromDate
start の呼び出しに多くの時間がかかります。私が行ったいくつかのプロファイリングによると、それらはかなり高価なようです。
たとえばNSArray *datesToCompare
、ある日付の配列からどれが特定の日と同じ日であるかを判断しようとしているとします。たとえばNSDate *baseDate
、次のようなものを使用できます(上記の回答から部分的に改作されています)。
NSDate *baseDate = [NSDate date];
NSArray *datesToCompare = [NSArray arrayWithObjects:[NSDate date],
[NSDate dateWithTimeIntervalSinceNow:100],
[NSDate dateWithTimeIntervalSinceNow:1000],
[NSDate dateWithTimeIntervalSinceNow:-10000],
[NSDate dateWithTimeIntervalSinceNow:100000],
[NSDate dateWithTimeIntervalSinceNow:1000000],
[NSDate dateWithTimeIntervalSinceNow:50],
nil];
// determine the NSDate for midnight of the base date:
NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* comps = [calendar components:(NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit)
fromDate:baseDate];
NSDate* theMidnightHour = [calendar dateFromComponents:comps];
// set up a localized date formatter so we can see the answers are right!
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
[dateFormatter setTimeStyle:NSDateFormatterMediumStyle];
// determine which dates in an array are on the same day as the base date:
for (NSDate *date in datesToCompare) {
NSTimeInterval interval = [date timeIntervalSinceDate:theMidnightHour];
if (interval >= 0 && interval < 60*60*24) {
NSLog(@"%@ is on the same day as %@", [dateFormatter stringFromDate:date], [dateFormatter stringFromDate:baseDate]);
}
else {
NSLog(@"%@ is NOT on the same day as %@", [dateFormatter stringFromDate:date], [dateFormatter stringFromDate:baseDate]);
}
}
出力:
Nov 23, 2011 1:32:00 PM is on the same day as Nov 23, 2011 1:32:00 PM
Nov 23, 2011 1:33:40 PM is on the same day as Nov 23, 2011 1:32:00 PM
Nov 23, 2011 1:48:40 PM is on the same day as Nov 23, 2011 1:32:00 PM
Nov 23, 2011 10:45:20 AM is on the same day as Nov 23, 2011 1:32:00 PM
Nov 24, 2011 5:18:40 PM is NOT on the same day as Nov 23, 2011 1:32:00 PM
Dec 5, 2011 3:18:40 AM is NOT on the same day as Nov 23, 2011 1:32:00 PM
Nov 23, 2011 1:32:50 PM is on the same day as Nov 23, 2011 1:32:00 PM