NetNewsWire/Multiplatform/iOS/Article/ImageScrollView.swift

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Swift
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//
// ImageScrollView.swift
// Multiplatform iOS
//
// Created by Maurice Parker on 7/6/20.
// Copyright © 2020 Ranchero Software. All rights reserved.
//
import UIKit
@objc public protocol ImageScrollViewDelegate: UIScrollViewDelegate {
func imageScrollViewDidGestureSwipeUp(imageScrollView: ImageScrollView)
func imageScrollViewDidGestureSwipeDown(imageScrollView: ImageScrollView)
}
open class ImageScrollView: UIScrollView {
@objc public enum ScaleMode: Int {
case aspectFill
case aspectFit
case widthFill
case heightFill
}
@objc public enum Offset: Int {
case begining
case center
}
static let kZoomInFactorFromMinWhenDoubleTap: CGFloat = 2
@objc open var imageContentMode: ScaleMode = .widthFill
@objc open var initialOffset: Offset = .begining
@objc public private(set) var zoomView: UIImageView? = nil
@objc open weak var imageScrollViewDelegate: ImageScrollViewDelegate?
var imageSize: CGSize = CGSize.zero
private var pointToCenterAfterResize: CGPoint = CGPoint.zero
private var scaleToRestoreAfterResize: CGFloat = 1.0
var maxScaleFromMinScale: CGFloat = 3.0
var zoomedFrame: CGRect {
return zoomView?.frame ?? CGRect.zero
}
override open var frame: CGRect {
willSet {
if frame.equalTo(newValue) == false && newValue.equalTo(CGRect.zero) == false && imageSize.equalTo(CGSize.zero) == false {
prepareToResize()
}
}
didSet {
if frame.equalTo(oldValue) == false && frame.equalTo(CGRect.zero) == false && imageSize.equalTo(CGSize.zero) == false {
recoverFromResizing()
}
}
}
override public init(frame: CGRect) {
super.init(frame: frame)
initialize()
}
required public init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
initialize()
}
private func initialize() {
showsVerticalScrollIndicator = false
showsHorizontalScrollIndicator = false
bouncesZoom = true
decelerationRate = UIScrollView.DecelerationRate.fast
delegate = self
}
@objc public func adjustFrameToCenter() {
guard let unwrappedZoomView = zoomView else {
return
}
var frameToCenter = unwrappedZoomView.frame
// center horizontally
if frameToCenter.size.width < bounds.width {
frameToCenter.origin.x = (bounds.width - frameToCenter.size.width) / 2
} else {
frameToCenter.origin.x = 0
}
// center vertically
if frameToCenter.size.height < bounds.height {
frameToCenter.origin.y = (bounds.height - frameToCenter.size.height) / 2
} else {
frameToCenter.origin.y = 0
}
unwrappedZoomView.frame = frameToCenter
}
private func prepareToResize() {
let boundsCenter = CGPoint(x: bounds.midX, y: bounds.midY)
pointToCenterAfterResize = convert(boundsCenter, to: zoomView)
scaleToRestoreAfterResize = zoomScale
// If we're at the minimum zoom scale, preserve that by returning 0, which will be converted to the minimum
// allowable scale when the scale is restored.
if scaleToRestoreAfterResize <= minimumZoomScale + CGFloat(Float.ulpOfOne) {
scaleToRestoreAfterResize = 0
}
}
private func recoverFromResizing() {
setMaxMinZoomScalesForCurrentBounds()
// restore zoom scale, first making sure it is within the allowable range.
let maxZoomScale = max(minimumZoomScale, scaleToRestoreAfterResize)
zoomScale = min(maximumZoomScale, maxZoomScale)
// restore center point, first making sure it is within the allowable range.
// convert our desired center point back to our own coordinate space
let boundsCenter = convert(pointToCenterAfterResize, to: zoomView)
// calculate the content offset that would yield that center point
var offset = CGPoint(x: boundsCenter.x - bounds.size.width/2.0, y: boundsCenter.y - bounds.size.height/2.0)
// restore offset, adjusted to be within the allowable range
let maxOffset = maximumContentOffset()
let minOffset = minimumContentOffset()
var realMaxOffset = min(maxOffset.x, offset.x)
offset.x = max(minOffset.x, realMaxOffset)
realMaxOffset = min(maxOffset.y, offset.y)
offset.y = max(minOffset.y, realMaxOffset)
contentOffset = offset
}
private func maximumContentOffset() -> CGPoint {
return CGPoint(x: contentSize.width - bounds.width,y:contentSize.height - bounds.height)
}
private func minimumContentOffset() -> CGPoint {
return CGPoint.zero
}
// MARK: - Set up
open func setup() {
var topSupperView = superview
while topSupperView?.superview != nil {
topSupperView = topSupperView?.superview
}
// Make sure views have already layout with precise frame
topSupperView?.layoutIfNeeded()
}
// MARK: - Display image
@objc open func display(image: UIImage) {
if let zoomView = zoomView {
zoomView.removeFromSuperview()
}
zoomView = UIImageView(image: image)
zoomView!.isUserInteractionEnabled = true
addSubview(zoomView!)
let tapGesture = UITapGestureRecognizer(target: self, action: #selector(doubleTapGestureRecognizer(_:)))
tapGesture.numberOfTapsRequired = 2
zoomView!.addGestureRecognizer(tapGesture)
let downSwipeGesture = UISwipeGestureRecognizer(target: self, action: #selector(swipeUpGestureRecognizer(_:)))
downSwipeGesture.direction = .down
zoomView!.addGestureRecognizer(downSwipeGesture)
let upSwipeGesture = UISwipeGestureRecognizer(target: self, action: #selector(swipeDownGestureRecognizer(_:)))
upSwipeGesture.direction = .up
zoomView!.addGestureRecognizer(upSwipeGesture)
configureImageForSize(image.size)
adjustFrameToCenter()
}
private func configureImageForSize(_ size: CGSize) {
imageSize = size
contentSize = imageSize
setMaxMinZoomScalesForCurrentBounds()
zoomScale = minimumZoomScale
switch initialOffset {
case .begining:
contentOffset = CGPoint.zero
case .center:
let xOffset = contentSize.width < bounds.width ? 0 : (contentSize.width - bounds.width)/2
let yOffset = contentSize.height < bounds.height ? 0 : (contentSize.height - bounds.height)/2
switch imageContentMode {
case .aspectFit:
contentOffset = CGPoint.zero
case .aspectFill:
contentOffset = CGPoint(x: xOffset, y: yOffset)
case .heightFill:
contentOffset = CGPoint(x: xOffset, y: 0)
case .widthFill:
contentOffset = CGPoint(x: 0, y: yOffset)
}
}
}
private func setMaxMinZoomScalesForCurrentBounds() {
// calculate min/max zoomscale
let xScale = bounds.width / imageSize.width // the scale needed to perfectly fit the image width-wise
let yScale = bounds.height / imageSize.height // the scale needed to perfectly fit the image height-wise
var minScale: CGFloat = 1
switch imageContentMode {
case .aspectFill:
minScale = max(xScale, yScale)
case .aspectFit:
minScale = min(xScale, yScale)
case .widthFill:
minScale = xScale
case .heightFill:
minScale = yScale
}
let maxScale = maxScaleFromMinScale*minScale
// don't let minScale exceed maxScale. (If the image is smaller than the screen, we don't want to force it to be zoomed.)
if minScale > maxScale {
minScale = maxScale
}
maximumZoomScale = maxScale
minimumZoomScale = minScale // * 0.999 // the multiply factor to prevent user cannot scroll page while they use this control in UIPageViewController
}
// MARK: - Gesture
@objc func doubleTapGestureRecognizer(_ gestureRecognizer: UIGestureRecognizer) {
// zoom out if it bigger than middle scale point. Else, zoom in
if zoomScale >= maximumZoomScale / 2.0 {
setZoomScale(minimumZoomScale, animated: true)
} else {
let center = gestureRecognizer.location(in: gestureRecognizer.view)
let zoomRect = zoomRectForScale(ImageScrollView.kZoomInFactorFromMinWhenDoubleTap * minimumZoomScale, center: center)
zoom(to: zoomRect, animated: true)
}
}
@objc func swipeUpGestureRecognizer(_ gestureRecognizer: UIGestureRecognizer) {
if gestureRecognizer.state == .ended {
imageScrollViewDelegate?.imageScrollViewDidGestureSwipeUp(imageScrollView: self)
}
}
@objc func swipeDownGestureRecognizer(_ gestureRecognizer: UIGestureRecognizer) {
if gestureRecognizer.state == .ended {
imageScrollViewDelegate?.imageScrollViewDidGestureSwipeDown(imageScrollView: self)
}
}
private func zoomRectForScale(_ scale: CGFloat, center: CGPoint) -> CGRect {
var zoomRect = CGRect.zero
// the zoom rect is in the content view's coordinates.
// at a zoom scale of 1.0, it would be the size of the imageScrollView's bounds.
// as the zoom scale decreases, so more content is visible, the size of the rect grows.
zoomRect.size.height = frame.size.height / scale
zoomRect.size.width = frame.size.width / scale
// choose an origin so as to get the right center.
zoomRect.origin.x = center.x - (zoomRect.size.width / 2.0)
zoomRect.origin.y = center.y - (zoomRect.size.height / 2.0)
return zoomRect
}
open func refresh() {
if let image = zoomView?.image {
display(image: image)
}
}
open func resize() {
self.configureImageForSize(self.imageSize)
}
}
extension ImageScrollView: UIScrollViewDelegate {
public func scrollViewDidScroll(_ scrollView: UIScrollView) {
imageScrollViewDelegate?.scrollViewDidScroll?(scrollView)
}
public func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
imageScrollViewDelegate?.scrollViewWillBeginDragging?(scrollView)
}
public func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
imageScrollViewDelegate?.scrollViewWillEndDragging?(scrollView, withVelocity: velocity, targetContentOffset: targetContentOffset)
}
public func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
imageScrollViewDelegate?.scrollViewDidEndDragging?(scrollView, willDecelerate: decelerate)
}
public func scrollViewWillBeginDecelerating(_ scrollView: UIScrollView) {
imageScrollViewDelegate?.scrollViewWillBeginDecelerating?(scrollView)
}
public func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
imageScrollViewDelegate?.scrollViewDidEndDecelerating?(scrollView)
}
public func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
imageScrollViewDelegate?.scrollViewDidEndScrollingAnimation?(scrollView)
}
public func scrollViewWillBeginZooming(_ scrollView: UIScrollView, with view: UIView?) {
imageScrollViewDelegate?.scrollViewWillBeginZooming?(scrollView, with: view)
}
public func scrollViewDidEndZooming(_ scrollView: UIScrollView, with view: UIView?, atScale scale: CGFloat) {
imageScrollViewDelegate?.scrollViewDidEndZooming?(scrollView, with: view, atScale: scale)
}
public func scrollViewShouldScrollToTop(_ scrollView: UIScrollView) -> Bool {
return false
}
@available(iOS 11.0, *)
public func scrollViewDidChangeAdjustedContentInset(_ scrollView: UIScrollView) {
imageScrollViewDelegate?.scrollViewDidChangeAdjustedContentInset?(scrollView)
}
public func viewForZooming(in scrollView: UIScrollView) -> UIView? {
return zoomView
}
public func scrollViewDidZoom(_ scrollView: UIScrollView) {
adjustFrameToCenter()
imageScrollViewDelegate?.scrollViewDidZoom?(scrollView)
}
}