UIPageViewController can return the wrong index - ios

Question

As the title states, there is a way it can return the wrong index. This messes up the index presentation dots at the bottom of the page. The way this is done is by skipping a page without releasing a finger from the screen. If this happens, it messes of the rest of the presentation dots.
here is what the bug it looks like in action.
And here is the code that was used for the UIPageViewController.
import UIKit
class PageViewController: UIPageViewController {
override func preferredStatusBarStyle() -> UIStatusBarStyle {
return UIStatusBarStyle.LightContent
}
private(set) lazy var orderedViewControllers: [UIViewController] = {
return [self.newColoredViewController("Green"),
self.newColoredViewController("Red"),
self.newColoredViewController("Blue")]
}()
private func newColoredViewController(color: String) -> UIViewController {
return UIStoryboard(name: "Main", bundle: nil) .
instantiateViewControllerWithIdentifier("\(color)ViewController")
}
override func viewDidLoad() {
super.viewDidLoad()
dataSource = self
if let firstViewController = orderedViewControllers.first {
setViewControllers([firstViewController],
direction: .Forward,
animated: true,
completion: nil)
}
// Do any additional setup after loading the view.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
/*
// MARK: - Navigation
// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
// Get the new view controller using segue.destinationViewController.
// Pass the selected object to the new view controller.
}
*/
}
//MARK: UIPageViewControllerDataSource
extension PageViewController: UIPageViewControllerDataSource {
func pageViewController(pageViewController: UIPageViewController, viewControllerBeforeViewController viewController: UIViewController) -> UIViewController? {
guard let viewControllerIndex = orderedViewControllers.indexOf(viewController) else {
return nil
}
let previousIndex = viewControllerIndex - 1
guard previousIndex >= 0 else {
return nil
}
guard orderedViewControllers.count > previousIndex else {
return nil
}
return orderedViewControllers[previousIndex]
}
func pageViewController(pageViewController: UIPageViewController, viewControllerAfterViewController viewController: UIViewController) -> UIViewController? {
guard let viewControllerIndex = orderedViewControllers.indexOf(viewController) else {
return nil
}
let nextIndex = viewControllerIndex + 1
let orderedViewControllersCount = orderedViewControllers.count
guard orderedViewControllersCount != nextIndex else {
return nil
}
guard orderedViewControllersCount > nextIndex else {
return nil
}
return orderedViewControllers[nextIndex]
}
func presentationCountForPageViewController(pageViewController: UIPageViewController) -> Int {
return orderedViewControllers.count
}
func presentationIndexForPageViewController(pageViewController: UIPageViewController) -> Int {
guard let firstViewController = viewControllers?.first,
firstViewControllerIndex = orderedViewControllers.indexOf(firstViewController) else {
return 0
}
return firstViewControllerIndex
}
}
Any help with this would be greatly appreciated, thanks.

Answer 1

I made a workaround because this is still not fixed!! It has been more than 4 years darn it.
Class to subclass instead of UIPageViewController:
import UIKit
class PageController: UIPageViewController {
lazy var pages: [UIViewController] = []
var newOffset: CGFloat = 20
var showReal = true
var pageControlX: CGFloat = 0 // 0 is the middle of the screen
var pageControlY: CGFloat = 200
private var scrollView: UIScrollView?
private var scrollPoints: [UIView] = []
private var oldScrollPoints: [UIView] = []
private var indexKeeper = IndexKeeper()
private var selectedColor = UIColor(white: 1, alpha: 1)
private var unselectedColor = UIColor(white: 1, alpha: 0.2)
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
// whole screen scroll
scrollView = view.subviews.filter{ $0 is UIScrollView }.first! as? UIScrollView
scrollView!.frame = UIScreen.main.bounds
// get pageControl and scroll view from view's subviews
let pageControl = view.subviews.filter{ $0 is UIPageControl }.first! as! UIPageControl
oldScrollPoints = pageControl.subviews
// remove all constraint from view that are tied to pageControl
let const = view.constraints.filter { $0.firstItem as? NSObject == pageControl || $0.secondItem as? NSObject == pageControl }
view.removeConstraints(const)
// customize pageControl
pageControl.translatesAutoresizingMaskIntoConstraints = false
pageControl.frame = CGRect(x: pageControlX, y: pageControlY,
width: view.frame.width, height: 0)
DispatchQueue.main.asyncAfter(deadline: .now() + 0.01) {
self.replacePoints()
self.updateIndex()
}
}
private func replacePoints() {
for point in scrollPoints {
point.removeFromSuperview()
}
scrollPoints = []
for oldPoint in oldScrollPoints {
let newPoint = UIView(frame: oldPoint.frame)
// make rounded
newPoint.layer.borderWidth = 0
newPoint.layer.masksToBounds = false
newPoint.layer.cornerRadius = newPoint.frame.height / 2
newPoint.clipsToBounds = true
newPoint.center = CGPoint(x: oldPoint.center.x, y: newOffset)
newPoint.backgroundColor = oldPoint.backgroundColor
oldPoint.superview?.addSubview(newPoint)
scrollPoints.append(newPoint)
oldPoint.alpha = showReal ? 1 : 0
}
}
private func offsetFromFirstPage() -> CGFloat {
var coordinates: [CGFloat] = []
for (index, page) in pages.enumerated() {
let offset = scrollView!.convert(scrollView!.bounds.origin, to: page.view!)
coordinates.append(offset.x + CGFloat(index) * view.frame.width)
}
let duplicates: [CGFloat] = coordinates.enumerated().map
{ current in
if coordinates.firstIndex(of: current.element) != coordinates.lastIndex(of: current.element) {
return current.element
} else {
return .nan
}
}
return duplicates.first(where: { !$0.isNaN }) ?? 0
}
private var lastIndex: Int = 0
private func pageIndexFrom(offset: CGFloat, visibleRatio: CGFloat=0.6) -> Int {
let adjustedOffset = (offset / view.frame.width)
if adjustedOffset > CGFloat(lastIndex) + visibleRatio {
if lastIndex + 1 < pages.count {
lastIndex += 1
}
} else if adjustedOffset < CGFloat(lastIndex) - visibleRatio {
if lastIndex - 1 >= 0 {
lastIndex -= 1
}
}
return lastIndex
}
private func updateIndex() {
let fastIndex = pages.firstIndex(of: viewControllers!.first!)!
indexKeeper.fastIndexUpdate(index: fastIndex)
let offset = offsetFromFirstPage()
let slowIndex = pageIndexFrom(offset: offset)
indexKeeper.slowIndexUpdate(index: slowIndex)
for (index, point) in scrollPoints.enumerated() {
if index == indexKeeper.finalIndex {
point.backgroundColor = selectedColor
} else {
point.backgroundColor = unselectedColor
}
}
DispatchQueue.main.asyncAfter(deadline: .now() + 0.01) {
self.updateIndex()
}
}
}
class IndexKeeper {
var finalIndex = 0
private var slowIndex = 0
private var fastIndex = 0
func slowIndexUpdate(index: Int) {
if index != slowIndex {
slowIndex = index
finalIndex = slowIndex
}
}
func fastIndexUpdate(index: Int) {
if index != fastIndex {
fastIndex = index
finalIndex = fastIndex
}
}
}
Example Use:
import UIKit
class PageViewController: PageController, UIPageViewControllerDataSource {
private func pageInstance(name:String) -> UIViewController {
return UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: name)
}
override func viewDidLoad() {
super.viewDidLoad()
pages = [
pageInstance(name: "FirstPage"),
pageInstance(name: "SecondPage"),
pageInstance(name: "ThirdPage"),
pageInstance(name: "FourthPage")
]
dataSource = self
setViewControllers([pages.first!], direction: .forward, animated: false, completion: nil)
}
// get page before current page
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
guard let index = pages.firstIndex(of: viewController), index > 0 else {
return nil
}
return pages[index - 1]
}
// get page after current page
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
guard let index = pages.firstIndex(of: viewController), index + 1 < pages.count else {
return nil
}
return pages[index + 1]
}
func presentationCount(for pageViewController: UIPageViewController) -> Int {
return pages.count
}
func presentationIndex(for pageViewController: UIPageViewController) -> Int {
if let vc = viewControllers?.first {
return pages.firstIndex(of: vc)!
}
return 0
}
}