Xcode How to calculate the number of month between two dates

I would like to calculate the amount of month since the last time an app has been started.

To do this, I save the current date at viewdidload to NSUserdefaults as String.

Bef开发者_如何学Pythonore I save the current date, I have to calculate the difference in month between the old(saved) date and the current date.

I am new in programming with NSDates, can someone tell me how to do this? And how to print the count in a lable?

Hope you understand what I mean and also someone could help me...

regards Dennis

The preferred way is to use NSCalendar.

-(int)differenceInMonthsFrom:(NSDate*)older to:(NSDate*)younger {
  NSCalendar *calendar=[NSCalendar currentCalendar];
  NSDateComponents *components=[calendar components:NSMonthCalendarUnit fromDate:older toDate:younger options:0];
  return [components month];
}

Note that this function does not check for ordering. Getting from your stored string to NSDate may be a trick; it might be wiser to store the date as an integer?

you have to use NSDate objects. for example :

 NSDate *now=[NSDate date];   // this is **now** date object
 NSDate *lastSaved=[NSdate lastDate];   // this is last saved object
 NSComparisonResult duration=[now timeIntervalSinceDate:lastSaved];   //this will return time interval between this 2 date object in seconds
 hoursInterval=duration/3600;  // this will return hours of interval between this 2 date
 daysInterval=hoursInterval/24;  // this will return days interval between this 2 date
 monthsInterval=daysInterval/30;  // and this will return month interval between this 2 date