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// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
import UIKit
/// A scroll view that adds a fade at top or bottom when it scroll
/// to indicate more content is available to user
public class FadeScrollView: UIScrollView, UIScrollViewDelegate {
private let fadePercentage: Double = 0.1
private let gradientLayer = CAGradientLayer()
private let transparentColor = UIColor.clear.cgColor
private let opaqueColor = UIColor.black.cgColor
private var needsToScroll: Bool {
return frame.size.height >= contentSize.height
}
private var isAtBottom: Bool {
return contentOffset.y + frame.size.height >= contentSize.height
}
private var isAtTop: Bool {
return contentOffset.y <= 0
}
private var topOpacity: CGColor {
let alpha: CGFloat = (needsToScroll || isAtTop) ? 1 : 0
return UIColor(white: 0, alpha: alpha).cgColor
}
private var bottomOpacity: CGColor {
let alpha: CGFloat = (needsToScroll || isAtBottom) ? 1 : 0
return UIColor(white: 0, alpha: alpha).cgColor
}
override public func layoutSubviews() {
super.layoutSubviews()
self.delegate = self
let maskLayer = CALayer()
maskLayer.frame = bounds
gradientLayer.frame = CGRect(x: bounds.origin.x,
y: 0,
width: bounds.size.width,
height: bounds.size.height)
gradientLayer.colors = [topOpacity, opaqueColor, opaqueColor, bottomOpacity]
gradientLayer.locations = [0,
NSNumber(value: fadePercentage),
NSNumber(value: 1 - fadePercentage),
1]
maskLayer.addSublayer(gradientLayer)
layer.mask = maskLayer
}
public func scrollViewDidScroll(_ scrollView: UIScrollView) {
gradientLayer.colors = [topOpacity, opaqueColor, opaqueColor, bottomOpacity]
}
}