How to detect that a UISlider has been tapped using RubyMotion?

Question

I have UISlider:

slider = UISlider.alloc.initWithFrame([[20, 70)], [260, 40]])

I want to be able to detect when the user clicks on it and know where. I figure that I'd need to use UITapGestureRecognizer or something similar, but I am very new and clueless to all this.

I can get to find out when the slider is tapped with this:

slider.addTarget(self, action:'sliderTaped', forControlEvents:UIControlEventTouchDown)

... but it only works on the thumb, so that's not very useful, I'd rather catch any tap on the slider.

Any pointers or links to documentation would be appreciated.

---

Related question/answer, but with objective-c: Clickable UISlider

Answer 1

To get notified when the slider has been changed, you need to set up the target/action. The target is the object containing the method you want called, and the action is the method you want called. I called my action sliderValueChanged:. You can choose anything. Be sure to append the colon to the name because that tells it to send a pointer to the sender which is the UISlider object. You need the sender so that you can ask for the value of the slider.

If you don't set a minimumValue and maximumValue for the slider, the values will range from 0.0 to 1.0.

def viewDidLoad
    slider = UISlider.alloc.initWithFrame([[20, 70], [260, 40]])
    slider.addTarget(self, action:'sliderValueChanged:', forControlEvents:UIControlEventValueChanged)
    self.view.addSubview(slider)
end

def sliderValueChanged(sender)
    puts sender.value
end

As shown, sliderValueChanged will get called continuously as the user moves the slider. To be notified only when the user stops touching the slider, set:

slider.continuous = no

Now, if you want a clickable slider that moves the thumb to where you click, then you need to add a UITapGestureRecognizer to the slider. This code demonstrates this:

def viewDidLoad
    slider = UISlider.alloc.initWithFrame([[50, 50], [200, 40]])
    tapGestureRecognizer = UITapGestureRecognizer.alloc.initWithTarget(self, action:'sliderTapped:')
    tapGestureRecognizer.numberOfTapsRequired = 2
    slider.addGestureRecognizer(tapGestureRecognizer)

    slider.continuous = false
    slider.minimumValue = 77
    slider.maximumValue = 129
    slider.addTarget(self, action:'sliderValueChanged:', forControlEvents:UIControlEventValueChanged)
    self.view.addSubview(slider)
end

# This is called when the slider changes either from taps or from moving the thumb
def handle_new_slider_value(value)
    puts "New slider value: #{value}"
end

def sliderValueChanged(slider)
    handle_new_slider_value(slider.value)
end

# These were determined empirically by setting the thumb to the minimum and
# then clicking on the center and printing out gestureRecognizer.locationInView(slider).x
# and then repeating for the maximum.
SLIDER_MIN = 11
SLIDER_MAX = 189

def sliderTapped(gestureRecognizer)
    if gestureRecognizer.state == UIGestureRecognizerStateEnded
        slider = gestureRecognizer.view
        x = gestureRecognizer.locationInView(slider).x
        # Uncomment this to determine values for SLIDER_MIN/SLIDER_MAX
        # puts x
        x = SLIDER_MIN if x < SLIDER_MIN
        x = SLIDER_MAX if x > SLIDER_MAX
        slider_min_val = slider.minimumValue
        slider_max_val = slider.maximumValue

        # Convert from the location in the view to the slider value
        slider.value = slider_min_val + (x - SLIDER_MIN) / (SLIDER_MAX - SLIDER_MIN) * (slider_max_val - slider_min_val)
        handle_new_slider_value(slider.value)
    end
end

Note that this code moves the slider on a double tap. I had trouble with just a single tap because if you move the thumb quickly, the code treats it as a tap and snaps the thumb back to its starting position. Set tapGestureRecognizer.numberOfTapsRequired = 1 to play around with the single tap.