How can I create reusable view controllers inside of UIScrollView? - ios

Question

I am trying to create a full page sized horizontally scrolling UIScrollView. On each page I am adding instances of the same UIViewController class. I would like to create some kind of reusable functionality to conserve both memory and processor use needed. Below is a basic implementation I have created with some toying around with how reusability might work although Im not quite sure. Thank you for any help you can offer.
Current UIScroll ViewController Model
let scrollView:UIScrollView = {
let scrollView = UIScrollView(frame: CGRect.zero)
scrollView.isPagingEnabled = true
scrollView.backgroundColor = UIColor.gray
scrollView.translatesAutoresizingMaskIntoConstraints = false
scrollView.showsVerticalScrollIndicator = false
scrollView.showsHorizontalScrollIndicator = true
return scrollView
}()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
scrollView.frame = CGRect(origin: CGPoint(x: 0, y: 0), size: self.view.bounds.size)
self.view.addSubview(scrollView)
scrollView.delegate = self
scrollView.contentSize = CGSize(width: 3 * self.view.frame.width, height: self.view.frame.height)
NSLayoutConstraint.activate([
scrollView.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 0),
scrollView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: 0),
scrollView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor, constant: 0),
scrollView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor, constant: 0)
])
let viewController1 = UIViewController()
viewController1.view.backgroundColor = UIColor.red
let viewController2 = UIViewController()
viewController2.view.backgroundColor = UIColor.blue
let viewController3 = UIViewController()
viewController3.view.backgroundColor = UIColor.green
self.addChild(viewController1)
viewController1.view.frame = CGRect(origin: CGPoint(x: 0, y: 0), size: self.view.bounds.size)
scrollView.addSubview(viewController1.view)
addViewControllerContraints(viewController: viewController1, index: 0)
viewController1.didMove(toParent: self)
self.addChild(viewController2)
viewController2.view.frame = CGRect(origin: CGPoint(x: self.view.bounds.width, y: 0), size: self.view.bounds.size)
scrollView.addSubview(viewController2.view)
addViewControllerContraints(viewController: viewController2, index: 1)
viewController2.didMove(toParent: self)
self.addChild(viewController3)
viewController3.view.frame = CGRect(origin: CGPoint(x: 2 * self.view.bounds.width, y: 0), size: self.view.bounds.size)
scrollView.addSubview(viewController3.view)
addViewControllerContraints(viewController: viewController3, index: 2)
viewController3.didMove(toParent: self)
}
func addViewControllerContraints( viewController: UIViewController, index:Int){
guard let view = viewController.view else{
print("View found nil")
return
}
view.translatesAutoresizingMaskIntoConstraints = false
let offset:CGFloat = UIScreen.main.bounds.width * CGFloat(index)
print("Offset: \(offset)")
NSLayoutConstraint.activate([
view.topAnchor.constraint(equalTo: scrollView.topAnchor, constant: 0),
view.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor, constant: offset),
view.heightAnchor.constraint(equalToConstant: self.view.bounds.height),
view.widthAnchor.constraint(equalToConstant: self.view.bounds.width)
])
}
Is there a good way to create some type of reuse functionality this is something I was playing around with based on This Answer although I realize that is primarily for UIPageViewControllers where allocation and deallocation of UIViewController's is handled for you.
Possible Reuse Functionality
var reuseableViewControllers:[UIViewController] = [UIViewController]()
private func unusedViewController() -> UIViewController {
let unusedViewControllers = reuseableViewControllers.filter { $0.parent == nil }
if let someUnusedViewController = unusedViewControllers.first {
return someUnusedViewController
} else {
let newViewController = UIViewController()
reuseableViewControllers.append(newViewController)
return newViewController
}
}