accessibilityIncrement / Decrement not called - ios

Question

I looked and cannot find an answer that works for me. I have subclassed UIControl to create a double-knob slider control. I want each knob to be available for voiceover.
To do this, I create UIAccessibilityElements and add them to an array:
func addAccessibilityElements() {
axKnobs = []
let lowKnob = UIAccessibilityElement(accessibilityContainer: self)
lowKnob.accessibilityLabel = doubleKnob ? lowValueKnobAccessibilityLabel : valueKnobAccessibilityLabel
lowKnob.accessibilityPath = UIAccessibilityConvertPathToScreenCoordinates(knobBezierPath(lowKnobPoint), self)
lowKnob.accessibilityTraits = UIAccessibilityTraitAdjustable
lowKnob.accessibilityValue = "\(lowValue)"
axKnobs.append(lowKnob)
if doubleKnob, let highKnobPoint = highKnobPoint {
let highKnob = UIAccessibilityElement(accessibilityContainer: self)
highKnob.accessibilityLabel = highValueKnobAccessibilityLabel
highKnob.accessibilityPath = UIAccessibilityConvertPathToScreenCoordinates(knobBezierPath(highKnobPoint), self)
highKnob.accessibilityTraits = UIAccessibilityTraitAdjustable
highKnob.accessibilityValue = "\(highValue)"
axKnobs.append(highKnob)
}
}
This seems to work perfect. These methods are called and the interface seems to work right:
override func accessibilityElementCount() -> Int {
return axKnobs.count
}
override func indexOfAccessibilityElement(element: AnyObject) -> Int {
let index = axKnobs.indexOf(element as! UIAccessibilityElement)!
if index == 0 {
currentKnob = .Low
} else {
currentKnob = .High
}
return index
}
override func accessibilityElementAtIndex(index: Int) -> AnyObject? {
return axKnobs[index]
}
However, my last 2 methods (accessibilityIncrement and accessibilityDecrement) in the class extension aren't being called at all.
override func accessibilityIncrement() {
if currentKnob == .None {
return
}
if currentKnob == .High {
highValue = max(highValue + 10, maximumValue)
} else {
if doubleKnob {
lowValue = max(lowValue + 10, highValue - 1)
} else {
lowValue = max(lowValue + 10, maximumValue)
}
}
updateDelegate()
redraw()
}
override func accessibilityDecrement() {
if currentKnob == .None {
return
}
if currentKnob == .High {
highValue = min(highValue - 10, lowValue + 1)
} else {
lowValue = min(lowValue - 10, minimumValue)
}
updateDelegate()
redraw()
}
Any ideas why? Full project available at https://github.com/AaronBratcher/SliderTest

Answer 1

UIAccessibilityElements have those 2 methods called, not the UIControl subclass.
extension DLSlider {
class KnobAccessibilityElement: UIAccessibilityElement {
var onIncrement: ((knob: UIAccessibilityElement) -> Void)?
var onDecrement: ((knob: UIAccessibilityElement) -> Void)?
override func accessibilityIncrement() {
if let callback = onIncrement {
callback(knob: self)
}
}
override func accessibilityDecrement() {
if let callback = onDecrement {
callback(knob: self)
}
}
}
func addAccessibilityElements() {
axKnobs = []
let lowKnob = KnobAccessibilityElement(accessibilityContainer: self)
lowKnob.accessibilityLabel = doubleKnob ? lowValueKnobAccessibilityLabel : valueKnobAccessibilityLabel
lowKnob.accessibilityPath = UIAccessibilityConvertPathToScreenCoordinates(knobBezierPath(lowKnobPoint), self)
lowKnob.accessibilityTraits = UIAccessibilityTraitAdjustable
lowKnob.accessibilityValue = "\(lowValue)"
lowKnob.onIncrement = { [unowned self] (knob: UIAccessibilityElement) in
self.incrementKnob(knob)
}
lowKnob.onDecrement = { [unowned self] (knob: UIAccessibilityElement) in
self.decrementKnob(knob)
}
axKnobs.append(lowKnob)
if doubleKnob, let highKnobPoint = highKnobPoint {
let highKnob = KnobAccessibilityElement(accessibilityContainer: self)
highKnob.accessibilityLabel = highValueKnobAccessibilityLabel
highKnob.accessibilityPath = UIAccessibilityConvertPathToScreenCoordinates(knobBezierPath(highKnobPoint), self)
highKnob.accessibilityTraits = UIAccessibilityTraitAdjustable
highKnob.accessibilityValue = "\(highValue)"
highKnob.onIncrement = { [unowned self] (knob: UIAccessibilityElement)in
self.incrementKnob(knob)
}
highKnob.onDecrement = { [unowned self] (knob: UIAccessibilityElement) in
self.decrementKnob(knob)
}
axKnobs.append(highKnob)
}
}
override func accessibilityElementCount() -> Int {
return axKnobs.count
}
override func indexOfAccessibilityElement(element: AnyObject) -> Int {
return axKnobs.indexOf(element as! UIAccessibilityElement)!
}
override func accessibilityElementAtIndex(index: Int) -> AnyObject? {
return axKnobs[index]
}
... // other methods here
}