Setting time on UISlider change

Question

I am working on setting time whenever a slider moves, I followed this link Slider with real time in Label and got most of the stuff working, here is the code, which I am presently working on

//This code is to check whether the system settings is 24hr format or 12hr format

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setLocale:[NSLocale currentLocale]];
[formatter setDateStyle:NSDateFormatterNoStyle];
[formatter setTimeStyle:NSDateFormatterShortStyle];
NSString *dateString = [formatter stringFromDate:[NSDate date]];
NSRange amRange = [dateString rangeOfString:[formatter AMSymbol]];
NSRange pmRange = [dateString rangeOfString:[formatter PMSymbol]];
m_is24h = (amRange.location == NSNotFound && pmRange.location == NSNotFound);

Here is the slider code

UISlider *slider = (UISlider *)sender;

NSUInteger numberOfSlots = 24*2 - 1; //total number of 30mins slots

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"h:mm a"];


NSDate *zeroDate;
NSString *amString = [[formatter AMSymbol]uppercaseString];
NSString *timeString = [[[NSString stringWithFormat:@"12:00"]stringByAppendingString:@" "]stringByAppendingString:amString];


if(m_is24h)
{
     zeroDate = [dateFormatter dateFromString:@"00:00"];
}
else
{
     zeroDate = [dateFormatter dateFromString:timeString];
}


NSUInteger actualSlot = roundf(numberOfSlots*slider.value);
NSTimeInterval slotInterval = actualSlot * 30 * 60;

NSDate *slotDate = [NSDate dateWithTimeInterval:slotInterval sinceDate:zeroDate];
[dateFormatter setDateFormat:@"h:mm a"];

m_timeLabel.text = [[dateFormatter stringFromDate:slotDate]uppercaseString];

I tested this code with India region and everything works fine both for 24hr and 12hr format.Now when I change the region to Japan or Europe or any other region, the 24 hour format will not work when I move the slider, but If I change the format to 12hr from settings, it works, I am not understanding what mistake I am doing here.

What exactly does "the 24 hour format will not work" mean? What happens? — user3071962, Apr 04 '14 at 12:05
I assume now that `[dateFormatter dateWithString:]` returns nil into zeroDate, because it cannot parse the string passed. All subsequent operations with zeroDate will also return nil. This should be easily verifiable in the debugger, right? — user3071962, Apr 04 '14 at 21:02
But why?...it works perfectly for india time zone and it works perfectly for 12hr format also — Ranjit, Apr 05 '14 at 04:45

score 3 · Accepted Answer · answered Apr 05 '14 at 07:49

I think you are overcomplicating what you are doing. You don't need to create a date for the slot with a string based on the 12 or 24 hour format that the user is using, you can just use an NSDate and let the formatter display the date appropriately.

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UILabel *timeLabel;
@property (weak, nonatomic) IBOutlet UISlider *slider;
@property (strong, nonatomic) NSDateFormatter *formatter;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.formatter = [NSDateFormatter new];
    [self.formatter setLocale:[NSLocale currentLocale]];
    [self.formatter setDateStyle:NSDateFormatterNoStyle];
    [self.formatter setTimeStyle:NSDateFormatterShortStyle];

    // Lazy way to set up the initial time
    [self sliderMoved:self.slider];

}

#pragma mark - Actions

- (IBAction)sliderMoved:(UISlider *)sender {
    NSUInteger slot = sender.value;
    NSDate *slotDate = [self timeFromSlot:slot];
    self.timeLabel.text = [self.formatter stringFromDate:slotDate];
}


#pragma mark - Private methods

/**
 Converts a slot integer to a valid time in 30 minute increments

 @param slot The slot number

 @return An NSDate for the time representing the slot

 @warning slot should be between 0 and 47
 */

- (NSDate *)timeFromSlot:(NSUInteger)slot{
    if ((slot > 47)) {
        return nil;
    }

    NSDateComponents *components = [NSDateComponents new];
    [components setMinute:30 * slot];

    return [[NSCalendar currentCalendar] dateFromComponents:components];
}

@end

This is the complete view controller implementation that does what you seem to want. The full project is available here if you don't want to create a test project yourself.

Thanks, this is exactly, what I was trying to achieve..I have a doubt though, why their is no need to do this [dateFormatter setDateFormat:@"h:mm a"]; — Ranjit, Apr 05 '14 at 08:34
Because of `[self.formatter setLocale:[NSLocale currentLocale]];` which uses the user's locale to decide whether to use 12 or 24 hour format. — Abizern, Apr 05 '14 at 08:37
@Abizern Please suggest http://stackoverflow.com/questions/33873530/i-want-to-switch-time-scrubber-to-do-15-min-intervals — Himanshu Parashar, Nov 24 '15 at 07:50

Setting time on UISlider change

1 Answers1