Вы должны реализовать datePickerValueChanged
в качестве селектора и реализовать таким образом.
- (void)datePickerValueChanged:(UIDatePicker*) date_Picker{
NSDateFormatter *df = [[NSDateFormatter alloc] init];
df.dateStyle = NSDateFormatterMediumStyle;
NSString *dateFromPicker = [NSString stringWithFormat:@"%@",[df stringFromDate:date_Picker.date]];
// calculating time difference now
NSDate *timeRightNow = [NSDate date];
NSTimeInterval diff = [timeRightNow timeIntervalSinceDate:date_Picker.date];
// The difference should always be in seconds. Here, 3628800 represents 6 weeks.
if (diff > 3628800){
// Do something if the entered date is six weeks from the iPhone date.
}
}