一：常规方法
- (NSInteger)daysFromDate:(NSDate *)startDate toDate:(NSDate *)endDate{
NSLog(@"start:%@", startDate);
NSLog(@"end:%@", endDate);
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
unsigned int unitFlags = NSDayCalendarUnit;
NSDateComponents *comps = [gregorian components:unitFlags fromDate:startDate toDate:endDate options:0];
return [comps day];
}
常规方法计算时间差，会被2个时间的时分秒所影响，打印时间如下
start:2014-01-19 04:15:22 +0000
end:2014-01-20 04:15:22 +0000
这样有可能会计算为0天。
二：强制计算方法
- (NSInteger)daysFromDate:(NSDate *)startDate toDate:(NSDate *)endDate{
NSDateFormatter *temp = [[NSDateFormatter alloc] init];
NSDate *stDt = [temp dateFromString:[temp stringFromDate:startDate]];
NSDate *endDt = [temp dateFromString:[temp stringFromDate:endDate]];
NSTimeZone *zone = [NSTimeZone systemTimeZone];
NSInteger interval = [zone secondsFromGMTForDate:stDt];
stDt = [stDt dateByAddingTimeInterval: interval];
interval = [zone secondsFromGMTForDate:endDt];
endDt = [endDt dateByAddingTimeInterval:interval];
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
unsigned int unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit;
NSDateComponents *comps = [gregorian components:unitFlags fromDate:stDt toDate:endDt options:0];
return [comps day];
}
