Convert circular, continuous UISlider value to a counter - ios

Question

In my app, I have created a circular, continuous slidable CircularSlider (this one). It has a minimumValue of 1.0 and a maximumValue of 10. Now, I'd like my users to be able to just keep sliding in circles to increase an NSInteger used somewhere in the app.
I tried doing that by writing the code below.
- (void)sliderChanged:(UICircularSlider *)slider {
int val = (int)slider.value;
slider.value = val;
int delta = val - self.oldValue;
if (self.oldValue == self.circularSlider.maximumValue && val == 0) {
delta = 1;
}
self.number += delta;
self.oldValue = val;
}
This works, but really sketch. Sometimes the value will drop by 10, caused by the slider giving me value of 10 and right afterwards a value of 0. It also doesn't work if the users starts scrubbing backwards and numbers start decreasing. I was wondering if there's a better way to achieve the same thing. Any ideas?

Answer 1

I think a better approach is to first figure out what direction the user moved. This can be done by checking which direction has the closest distance between the new and the old position. Care must be taken to check for passing the border. Then it is a simple matter of adjusting the delta depending on direction.
My solution code assumes the the slider starts at zero, which I would recommend you to use instead of 1, since calculations are easier. If you really want to start at 1 it can be adjusted. I also have defined the maximum value as a constant SLIDER_MAX_VALUE, which you could change to a variable instead. Finally, I changed self.number to a CGFloat, so do the cast when using the number instead. This is important, otherwise you get rounding errors when sliding. If you really want an integer, use two variables, and assign the integer variable from the float.
#define SLIDER_MAX_VAL 10
- (void)sliderChanged:(UICircularSlider *)slider {
CGFloat delta = slider.value - self.oldValue;
if ((delta > 0 && delta < SLIDER_MAX_VAL / 2) ||
(delta < 0 && delta < -SLIDER_MAX_VAL / 2)) {
// Moving forward
if (delta < 0)
delta += SLIDER_MAX_VAL;
} else {
// Moving backward
if (delta > 0)
delta -= SLIDER_MAX_VAL;
}
self.number += delta; // Change to CGFloat
self.oldValue = slider.value;
}