Assign UIScrollView Delegate And UICollectionView Delegate to the Same Class

I have a paging UIScrollView, each page being populated with a different view controller. Above the scrollview is a UICollectionView that acts as a menu bar. As you scroll through the scrollview pages, the menu bar moves just a little bit. You can see from the gif on the left.

Setting their delegates to different classes keeps everything working correctly as seen in the gif on the left. BUT, setting them to the same class messes up the UICollectionViews behavior.

How do I set their delegates to the same class?

import UIKit

class MenuView: UIView, UICollectionViewDataSource {

    let collcetionView: UICollectionView = {
        let view = UICollectionView()
        // Setup...
        return view
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupCollectionView()
        collcetionView.dataSource = self
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    fileprivate func setupCollectionView() {
        // Autolayout code...
    }

    // Datasource methods to populate collection view cells
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    // Populate cell code...
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        // Populate cell code...
    }
}


class MainView: UIView {
    // Contains paging scroll view and menu bar
    var menu: MenuView!

    let scrollView: UIScrollView = {
        let view = UIScrollView()
        // Setup...
        return view
    }()

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupMenu()
        setupScrollView()

    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    fileprivate func setupScrollView() {
        // Autolayout code...
    }
    fileprivate func setupMenu() {
        menu = MenuView()
        // Autolayout code...
    }
}


class MainController: UIViewController, UIScrollViewDelegate, UICollectionViewDelegate {
    var mainView: MainView!

    override func loadView() {
        super.loadView()
        mainView = MainView()
        view = mainView
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        mainView.scrollView.delegate = self
        mainView.menu.collcetionView.delegate = self // <<--- THIS IS WHAT BREAKS EVERYTHING
    }


func scrollViewDidScroll(_ scrollView: UIScrollView) {

        // Moving menu bar with page scroll
        mainView.menu.collectionView.contentOffset = CGPoint(x: scrollView.contentOffset.x/SCROLL_FACTOR - (firstIndexPosition/SCROLL_FACTOR - difference/2), y: 0)



        // Fade in and out highlighted state of menu bar cell
        let exactPage = (scrollView.contentOffset.x / SCREEN_WIDTH)
        let currentPage = (scrollView.contentOffset.x / SCREEN_WIDTH).rounded()
        let unitExact = currentPage - exactPage
        //print(String(format: "exact: %.2f, ", exactPage) + "current: \(currentPage), " + String(format: "unit: %.2f, ", unitExact))

        if exactPage > currentPage {
            // exact > current
            // fade out/in left icon
            // select current
            let unit = 0 - unitExact // from 0 - 0.5
            let cell = mainView.menu.collectionView.cellForItem(at: IndexPath(item: Int(currentPage), section: 0)) as! MenuBarCell
            let mapped = unit.map(from: 0.0...0.5, to: 0...149.0)
            print(cell)
            setCellColor(cell: cell, value: mapped)
        } else if exactPage < currentPage {
            // exact < current
            // fade out/in right icon
            // select current
            let unit = unitExact // from 0 - 0.5
            let cell = mainView.menu.collectionView.cellForItem(at: IndexPath(item: Int(currentPage), section: 0)) as! MenuBarCell
            let mapped = unit.map(from: 0.0...0.5, to: 0...149.0)
            setCellColor(cell: cell, value: mapped)
        } else if exactPage == currentPage {
            // exact = current
            // darken that icon
            // select current
        }
    }
}

UICollectionView and UITableView inherit from UIScrollView,

The scrollViewDidScroll delegate method will be called for both your collection view and your scrollview if you set the delegate for both objects to the same class.

You need to check why scrollViewDidScroll is being called and act accordingly.

The simplest approach is a guard statement that returns if the delegate method isn't called for the scroll view you are interested in.

If you needed to execute different code depending on the scroll view involved you could use a series of if statements or a switch statement.

func scrollViewDidScroll(_ scrollView: UIScrollView) {

   guard scrollView == self.scrollView else {
       return
   }

    // Moving menu bar with page scroll
    mainView.menu.collectionView.contentOffset = CGPoint(x: scrollView.contentOffset.x/SCROLL_FACTOR - (firstIndexPosition/SCROLL_FACTOR - difference/2), y: 0)



    // Fade in and out highlighted state of menu bar cell
    let exactPage = (scrollView.contentOffset.x / SCREEN_WIDTH)
    let currentPage = (scrollView.contentOffset.x / SCREEN_WIDTH).rounded()
    let unitExact = currentPage - exactPage
    //print(String(format: "exact: %.2f, ", exactPage) + "current: \(currentPage), " + String(format: "unit: %.2f, ", unitExact))

    if exactPage > currentPage {
        // exact > current
        // fade out/in left icon
        // select current
        let unit = 0 - unitExact // from 0 - 0.5
        let cell = mainView.menu.collectionView.cellForItem(at: IndexPath(item: Int(currentPage), section: 0)) as! MenuBarCell
        let mapped = unit.map(from: 0.0...0.5, to: 0...149.0)
        print(cell)
        setCellColor(cell: cell, value: mapped)
    } else if exactPage < currentPage {
        // exact < current
        // fade out/in right icon
        // select current
        let unit = unitExact // from 0 - 0.5
        let cell = mainView.menu.collectionView.cellForItem(at: IndexPath(item: Int(currentPage), section: 0)) as! MenuBarCell
        let mapped = unit.map(from: 0.0...0.5, to: 0...149.0)
        setCellColor(cell: cell, value: mapped)
    } else if exactPage == currentPage {
        // exact = current
        // darken that icon
        // select current
    }
}