UISlider get Value while Anmation runs - ios

Question

I animate a UISlider with this function:
func animateSlider(){
slider.value = Float(min)
UIView.animate(withDuration: 2.0, animations: {
self.slider.setValue(Float(self.max), animated:true)
})
When I tap the screen I want to get the current value but it only returns the maximum value. What can I do to solve that problem?

Answer 1

When you schedule an animation Core Animation sets the model layer's properties immediately, and the creates a presentation layer which you may inspect. This presentation layer is what you actually see on screen, and is valid to query its properties such as its frame, bounds, position, etc.
You were asking for the model layer's value which is set immediately in your animation block, when instead what you want is what is displayed through the presentation layer.
You can get the currently displayed presentation value from the label when there is an in-progress animation by using this extension on UISlider:
extension UISlider {
var currentPresentationValue: Float {
guard let presentation = layer.presentation(),
let thumbSublayer = presentation.sublayers?.max(by: {
$0.frame.height < $1.frame.height
})
else { return self.value }
let bounds = self.bounds
let trackRect = self.trackRect(forBounds: bounds)
let minRect = self.thumbRect(forBounds: bounds, trackRect: trackRect, value: 0)
let maxRect = self.thumbRect(forBounds: bounds, trackRect: trackRect, value: 1)
let value = (thumbSublayer.frame.minX - minRect.minX) / (maxRect.minX - minRect.minX)
return Float(value)
}
}
And its usage:
func animateSlider() {
slider.value = 0
DispatchQueue.main.async {
UIView.animate(withDuration: 2, delay: 0, options: .curveLinear, animations: {
self.slider.setValue(1, animated: true)
}, completion: nil)
}
// quarter done:
DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
print(self.slider.currentPresentationValue)
// prints 0.272757, expected 0.25 with some tolerance
}
// half done:
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
print(self.slider.currentPresentationValue)
// prints 0.547876, expected 0.5 with some tolerance
}
// three quarters done:
DispatchQueue.main.asyncAfter(deadline: .now() + 1.5) {
print(self.slider.currentPresentationValue)
// prints 0.769981, expected 0.75 with some tolerance
}
}

Answer 2

I don't think that a slider's value property can be animated using UIView.animate(). However, if you read the documentation on UISlider, you'll find the function
func setValue(Float, animated: Bool)
Use that to animate your slider to a new position.
If you want to animate a change over a longer time period like 2 seconds, though, you'll probably have to set up a repeating timer or a CADisplayLink timer that changes the slider value by small increments each time it fires.
As for your statement "When I tap the screen I want to get the current value but it only returns the maximum" That is the way Cocoa animation works. You can't interrogate an in-flight animation and get a value that's the value of the property you are animating at that instant. (You could do that if you used a repeating timer to animate the slider though.)