I think you connected your segue with view controller not with navigation controller. To fix this replace your code with:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([segue.identifier isEqualToString:@"AddDate"])
{
DatePickerViewController *datePickerViewController = (DatePickerViewController*)segue.destinationViewController;
datePickerViewController.delegate = self;
}
}