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POiPhone - get number of days between two dates
 

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  1. POiPhone - get number of days between two dates
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    <p>I'm writing a GTD app for the iPhone. For the due tasks, I want to display something like "Due tomorrow" or "Due yesterday" or "Due July 18th". Obviously, I need to display "Tomorrow" even if the task is less than 24 hours away (e.g. the user checks at 11pm on Saturday and sees there's a task on Sunday at 8am). So, I wrote a method to get the number of days in between two dates. Here's the code...</p> <pre><code>NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setDateFormat:@"yyyy-MM-dd-HH-mm"]; NSDate *nowDate = [dateFormatter dateFromString:@"2010-01-01-15-00"]; NSDate *dueDate = [dateFormatter dateFromString:@"2010-01-02-14-00"]; NSLog(@"NSDate *nowDate = %@", nowDate); NSLog(@"NSDate *dueDate = %@", dueDate); NSCalendar *calendar = [NSCalendar currentCalendar]; NSDateComponents *differenceComponents = [calendar components:(NSDayCalendarUnit) fromDate:nowDate toDate:dueDate options:0]; NSLog(@"Days between dates: %d", [differenceComponents day]); </code></pre> <p>... and here's the output:</p> <pre><code>NSDate *nowDate = 2010-01-01 15:00:00 -0700 NSDate *dueDate = 2010-01-02 14:00:00 -0700 Days between dates: 0 </code></pre> <p>As you can see, the method returns incorrect results. It should have returned 1 as the number of days between the two days. What am I doing wrong here?</p> <p>EDIT: I wrote another method. I haven't done extensive unit tests, but so far it seems to work:</p> <pre><code>+ (NSInteger)daysFromDate:(NSDate *)fromDate inTimeZone:(NSTimeZone *)fromTimeZone untilDate:(NSDate *)toDate inTimeZone:(NSTimeZone *)toTimeZone { NSCalendar *calendar = [NSCalendar currentCalendar]; unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit; [calendar setTimeZone:fromTimeZone]; NSDateComponents *fromDateComponents = [calendar components:unitFlags fromDate:fromDate]; [calendar setTimeZone:toTimeZone]; NSDateComponents *toDateComponents = [calendar components:unitFlags fromDate:toDate]; [calendar setTimeZone:[NSTimeZone defaultTimeZone]]; NSDate *adjustedFromDate = [calendar dateFromComponents:fromDateComponents]; NSDate *adjustedToDate = [calendar dateFromComponents:toDateComponents]; NSTimeInterval timeIntervalBetweenDates = [adjustedToDate timeIntervalSinceDate:adjustedFromDate]; NSInteger daysBetweenDates = (NSInteger)(timeIntervalBetweenDates / (60.0 * 60.0 * 24.0)); NSDateComponents *midnightBeforeFromDateComponents = [[NSDateComponents alloc] init]; [midnightBeforeFromDateComponents setYear:[fromDateComponents year]]; [midnightBeforeFromDateComponents setMonth:[fromDateComponents month]]; [midnightBeforeFromDateComponents setDay:[fromDateComponents day]]; NSDate *midnightBeforeFromDate = [calendar dateFromComponents:midnightBeforeFromDateComponents]; [midnightBeforeFromDateComponents release]; NSDate *midnightAfterFromDate = [[NSDate alloc] initWithTimeInterval:(60.0 * 60.0 * 24.0) sinceDate:midnightBeforeFromDate]; NSTimeInterval timeIntervalBetweenToDateAndMidnightBeforeFromDate = [adjustedToDate timeIntervalSinceDate:midnightBeforeFromDate]; NSTimeInterval timeIntervalBetweenToDateAndMidnightAfterFromDate = [adjustedToDate timeIntervalSinceDate:midnightAfterFromDate]; if (timeIntervalBetweenToDateAndMidnightBeforeFromDate &lt; 0.0) { // toDate is before the midnight before fromDate timeIntervalBetweenToDateAndMidnightBeforeFromDate -= daysBetweenDates * 60.0 * 60.0 * 24.0; if (timeIntervalBetweenToDateAndMidnightBeforeFromDate &lt; 0.0) daysBetweenDates -= 1; } else if (timeIntervalBetweenToDateAndMidnightAfterFromDate &gt;= 0.0) { // toDate is after the midnight after fromDate timeIntervalBetweenToDateAndMidnightAfterFromDate -= daysBetweenDates * 60.0 * 60.0 * 24.0; if (timeIntervalBetweenToDateAndMidnightAfterFromDate &gt;= 0.0) daysBetweenDates += 1; } [midnightAfterFromDate release]; return daysBetweenDates; } </code></pre>
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