UIDatePicker时间

Question

I have a UIDatePicker and a button. When I press the button I want to display in the log the message "Setting a reminder for x" where x is the time displayed by the date picker.

Everytime I press the button, the time logged is precisely 3 hours behind the time displayed by the picker (the time displayed by the picker is my current time). I suspect it has something to do with the time zone. I live in GMT +2 time zone (I guess it's +3 since we are in daylight saving time).

Do you have any idea how I could make the time logged to be the same as the time displayed?

Below is the method that gets executed when I press the button. Thanks.

- (IBAction)addReminder:(id)sender {
    [self.datePicker setTimeZone:[NSTimeZone systemTimeZone]];
    NSLog(@"Setting a reminder for %@", self.datePicker.date);
}

Answer 1

NSDate is simple representation of some moment in time, it knows nothing about your local time. When you log it (actually, when description ) message is sent, it uses GMT to display itself.

UIDatePicker uses your timezone by default (see https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIDatePicker_Class/#//apple_ref/occ/instp/UIDatePicker/timeZone ).

So, here is how it works:

• You choose some time in DatePicker, but time is meaningless unless you specify timezone.
• DatePicker uses your local (GMT+2) timezone and creates NSDate for it.
• You display NSDate and since it knows nothing about timezone, it simply displays itself as GMT.

To display your date, your should use NSDateFormatter . It has Timezone property: https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSDateFormatter_Class/#//apple_ref/occ/instp/NSDateFormatter/timeZone

You can also use NSCalendar and its components.

You should read this guide: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/DatesAndTimes/DatesAndTimes.html since dates, formatters and calendars are not very clear in Cocoa unless you understand its concepts.

Answer 2

Try this...

NSDate *now = [[NSDate alloc] init];
[self.datePicker setDate:now];
[self.picker setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:2*60*60]]; // GMT+2 Your timeZone
NSLog(@"Setting a reminder for %@", self.datePicker.date);