从UIDatePicker中选择的日期与保存的日期不同

Question

This is how I setup my datePicker

self.datePicker = [[UIDatePicker alloc] init];
self.datePicker.timeZone = [NSTimeZone localTimeZone];

This is how I save the date that I selected

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateStyle:NSDateFormatterMediumStyle];
[formatter setTimeZone:[NSTimeZone localTimeZone]];
dateToSave = [formatter dateFromString:self.dateTextField.text];
NSLog(@"date saved = %@", dateToSave);

If I select Nov 18 2013 from the date picker, the NSLog shows

date saved = 2013-11-17 16:00:00 +0000

However, somewhere in my code, I need to get the difference in days between today's date and the date that I selected in the datepicker.

NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:NSDayCalendarUnit fromDate:[NSDate date] toDate:dateSaved options:0];
NSLog(@"number of days => %i", [dateComponents day]);

Today is Nov 10. The date I saved is Nov 18. But the number of days difference is 7, instead of 8.

Answer 1

Your time zone is -8. 2013-11-17 16:00:00 +0000 equals to 2013-11-18 00:00:00 -0800 .

Use [NSTimeZone timeZoneForSecondsFromGMT:0] instead of [NSTimeZone localTimeZone]

Answer 2

(This answer refers to the updated question about calculating the number of days between two dates.)

The problem is that [NSDate date] is the current date+time, not the start of the current day. For example, if

 [NSDate date] = "2013-11-10 10:00:00"
 dateSaved     = "2013-11-18 00:00:00"    (both in your *local* timezone)

then the difference between these two dates is "7 days and 14 hours". Therefore you get 7 as the number of days.

So you have to calculate the start of the current day first:

NSDate *startOfDay;
[[NSCalendar currentCalendar] rangeOfUnit:NSDayCalendarUnit
                                startDate:&startOfDay
                                 interval:NULL
                                  forDate:[NSDate date]];

and then use it in the calculation of the difference:

NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:NSDayCalendarUnit
                                           fromDate:startOfDay
                                             toDate:dateSaved
                                            options:0];

Answer 3

NSDateFormatter *date_form=[[NSDateFormatter alloc]init];

[date_form setDateFormat:@"dd/MM/yyyy"];

NSDate *seletected_date = [datepicker date];

NSString *dateToSave=[[NSString alloc] initWithFormat:@"%@",[date_form stringFromDate:seletected_date]]; 

NSLog(@"date saved = %@", dateToSave);

Remove localtimezone