Labels for UISlider values and centering text - ios

Question

I have a slider and would like to display text labels for some of the values on the slider.
I would like numbers to be centered on top of values. Labels are of fixed width - predefined. So I think all I need to do is calculate space width in between labels and keep incrementing x position when positioning each label. The problem that I am seeing though is there more labels there are the more each label slides to the right. I know this because the value set is always in the center of the slider in my test cases. Text is centered within label. Please see pictures on the first picture labels are almost correctly centered. The way to see what I mean is looking at the last label in both pictures. I almost think that it is the border of the label perhaps but I do not set the border either. I am not sure what I could be doing wrong in terms of math, but must be missing something. Also, it seems like the fir label maybe more than 1/2 label width of to the left of slider start position.
EDIT This is because the frame X starting position DOES not match the x starting position of the slider. See pic. Now I just need to figure out how to calculate the offset. The red line is drawn at slider.frame.origin.x. You can see that slider is off by a few points. The ball should be in the center at 3.125 - 25 .. but it is slightly of.
The way space between labels is calculated:
float xPosition = sliderFrame.origin.x;
//Slider adjusted width
float sliderWidth = sliderFrame.size.width - xPosition;
float spacedApart = (sliderWidth - (LABEL_WIDTH * numberofticks)) / (float) (numberofticks);
Each label is displayed at:
CGRect mpkLabelFrame = CGRectMake(xPosition - LABEL_WIDTH/2, (yPosition - spaceBetweenLabelsAndSlider), LABEL_WIDTH, LABEL_HEIGHT)+3; //need to increase by 3 to make it work better
//display label do other things
xPosition += (LABEL_WIDTH + spacedApart);

Answer 1

You don't need to take into account the sliders x coordinate to figure out the spacing. In fact, since they are distributed equally you don't need the label size as well.
CGFloat labelSpacing = sliderFrame.size.width/(numberOfTicks-1);
xPosition = sliderFrame.origin.x;
Set the label's frames:
CGRect mpkLabelFrame = CGRectMake(xPosition - LABEL_WIDTH/2, (yPosition - spaceBetweenLabelsAndSlider), LABEL_WIDTH, LABEL_HEIGHT);
xPosition += labelSpacing;
EDIT: code for testing the approach in an viewController:
- (void)viewDidLoad{
[super viewDidLoad];
self.view.backgroundColor = [UIColor whiteColor];
UISlider *slider = [[UISlider alloc] initWithFrame:CGRectMake(40, 100, 240, 10)];
[self.view addSubview:slider];
int numberOfTicks = 7;
CGFloat labelSpacing = slider.frame.size.width/(numberOfTicks-1);
CGFloat xPosition = slider.frame.origin.x;
CGFloat labelWidth = 10;
CGFloat yPosition = CGRectGetMinY(slider.frame)-20;
for (int i=0;i<numberOfTicks;i++){
CGRect labelFrame = CGRectMake(xPosition - labelWidth/2, (yPosition), labelWidth, 20);
UILabel *label = [[UILabel alloc] initWithFrame:labelFrame];
label.backgroundColor = [UIColor redColor];
label.adjustsFontSizeToFitWidth = YES;
label.text = [NSString stringWithFormat:#"%i",i];
[self.view addSubview:label];
xPosition += labelSpacing;
}
}