在swift 3中检测uislider拇指拖动的方向

let slider = UISlider(frame: CGRect(x: 0, y: 0, width: 200, height: 20))
slider.minimumValue = 0
slider.maximumValue = 100
slider.value = 50

slider.addTarget(self, action: #selector(sliderValueChanged(_:)), for: .valueChanged)

@objc func sliderValueChanged(_ sender: UISlider) {
    let currentValue = sender.value
    let previousValue = sender.previousValue ?? currentValue
    
    if currentValue > previousValue {
        print("向右拖动")
    } else if currentValue < previousValue {
        print("向左拖动")
    } else {
        print("未拖动")
    }
    
    sender.previousValue = currentValue
}