I have a class that subclasses a UIPageViewController that which contains 4 controllers, I am trying to figure out how I can change color of the button as I scroll halfway to the second view controller
The button color should be different only on the first controller
This code here almost works but the behaviour is not correct only for the third controller which means the solution is not correct.
I Would really appreciate it if someone could help out. Thanks
public func scrollViewDidScroll(_ scrollView: UIScrollView) {
let point = scrollView.contentOffset
let width = scrollView.frame.width
let percentComplete = abs(point.x - width) / width
let page = Int(round(percentComplete))
if percentComplete >= 0.5 {
if page == 1, currentIndex == 1 {
nextButton.backgroundColor = .red
} else {
nextButton.backgroundColor = .blue
}
print ("percentComplete: ", percentComplete,
"page: ", page,
"currentIndex: ",
currentIndex, "point: ", point.x)
}
}
Even though you say you want to use UIPageViewController, here is an example implementation using UIScrollView that you may find easier to manage:
class PagedScrollViewController: UIViewController, UIScrollViewDelegate {
let scrollView: UIScrollView = {
let v = UIScrollView()
v.isPagingEnabled = true
v.bounces = false
return v
}()
let pageControl: UIPageControl = {
let v = UIPageControl()
return v
}()
let stack: UIStackView = {
let v = UIStackView()
v.axis = .horizontal
v.distribution = .fillEqually
return v
}()
var pages: [UIViewController] = []
override func viewDidLoad() {
super.viewDidLoad()
scrollView.translatesAutoresizingMaskIntoConstraints = false
pageControl.translatesAutoresizingMaskIntoConstraints = false
stack.translatesAutoresizingMaskIntoConstraints = false
scrollView.addSubview(stack)
view.addSubview(scrollView)
view.addSubview(pageControl)
let g = view.safeAreaLayoutGuide
let svCLG = scrollView.contentLayoutGuide
let svFLG = scrollView.frameLayoutGuide
NSLayoutConstraint.activate([
scrollView.topAnchor.constraint(equalTo: g.topAnchor, constant: 20.0),
scrollView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 20.0),
scrollView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -20.0),
scrollView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -80.0),
stack.topAnchor.constraint(equalTo: svCLG.topAnchor, constant: 0.0),
stack.leadingAnchor.constraint(equalTo: svCLG.leadingAnchor, constant: 0.0),
stack.trailingAnchor.constraint(equalTo: svCLG.trailingAnchor, constant: 0.0),
stack.bottomAnchor.constraint(equalTo: svCLG.bottomAnchor, constant: 0.0),
stack.heightAnchor.constraint(equalTo: svFLG.heightAnchor, constant: 0.0),
pageControl.topAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: 8.0),
pageControl.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor),
pageControl.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor),
])
// if we're loading "page" view controllers from Storyboard
/*
if let vc = storyboard?.instantiateViewController(withIdentifier: "psFirst") as? PSFirstViewController {
pages.append(vc)
}
if let vc = storyboard?.instantiateViewController(withIdentifier: "psSecond") as? PSSecondViewController {
pages.append(vc)
}
if let vc = storyboard?.instantiateViewController(withIdentifier: "psThird") as? PSThirdViewController {
pages.append(vc)
}
if let vc = storyboard?.instantiateViewController(withIdentifier: "psFourth") as? PSFourthViewController {
pages.append(vc)
}
pages.forEach { vc in
self.addChild(vc)
stack.addArrangedSubview(vc.view)
vc.view.widthAnchor.constraint(equalTo: scrollView.frameLayoutGuide.widthAnchor, constant: 0.0).isActive = true
vc.didMove(toParent: self)
}
*/
// for this example,
// create 4 view controllers, with background colors
let colors: [UIColor] = [
.red, .brown, .blue, .magenta
]
colors.forEach { c in
let vc = BasePageController()
vc.view.backgroundColor = c
self.addChild(vc)
stack.addArrangedSubview(vc.view)
vc.view.widthAnchor.constraint(equalTo: scrollView.frameLayoutGuide.widthAnchor, constant: 0.0).isActive = true
vc.didMove(toParent: self)
pages.append(vc)
}
pageControl.numberOfPages = pages.count
scrollView.delegate = self
pageControl.addTarget(self, action: #selector(self.pgControlChange(_:)), for: .valueChanged)
}
var pgControlScroll: Bool = false
@objc func pgControlChange(_ sender: UIPageControl) {
pgControlScroll = true
let w = scrollView.frame.size.width
guard w != 0 else { return }
let x = scrollView.contentOffset.x
let cp = min(Int(round(x / w)), pages.count - 1)
let np = sender.currentPage
var r = CGRect.zero
if np > cp {
r = CGRect(x: w * CGFloat(np + 1) - 1.0, y: 0, width: 1, height: 1)
} else {
r = CGRect(x: w * CGFloat(np), y: 0, width: 1, height: 1)
}
scrollView.scrollRectToVisible(r, animated: true)
}
func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
pgControlScroll = false
}
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let w = scrollView.frame.size.width
guard w != 0 else { return }
let x = scrollView.contentOffset.x
let pg = min(Int(round(x / w)), pages.count - 1)
let v = stack.arrangedSubviews[pg]
pageControl.backgroundColor = v.backgroundColor
if pgControlScroll { return }
pageControl.currentPage = pg
}
}
class BasePageController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// add a label at each corner
for (i, s) in ["top-left", "top-right", "bot-left", "bot-right"].enumerated() {
let v = UILabel()
v.backgroundColor = UIColor(white: 0.8, alpha: 1.0)
v.translatesAutoresizingMaskIntoConstraints = false
v.text = s
view.addSubview(v)
let g = view.safeAreaLayoutGuide
switch i {
case 1:
v.topAnchor.constraint(equalTo: g.topAnchor, constant: 4.0).isActive = true
v.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -4.0).isActive = true
case 2:
v.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -4.0).isActive = true
v.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 4.0).isActive = true
case 3:
v.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: -4.0).isActive = true
v.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -4.0).isActive = true
default:
v.topAnchor.constraint(equalTo: g.topAnchor, constant: 4.0).isActive = true
v.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 4.0).isActive = true
}
}
}
}
The code adds a scroll view that takes up most of the screen (with some padding so the frame of the scroll view is obvious), with a UIPageControl underneath.
We add 4 view controllers as child view controllers, and add their views to a UIStackView in the scroll view.
When you scroll from "page-to-page" the page control will update and change background color as you get half-way to the next / previous page.
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