Nothing Occurring with ScrollToItem in UICollectionView - swift

Question

I have two collection views within a ViewController. One Collection view represents the tab bar at the top, the other represents pages on the bottom half of the screen. I have the second UICollectionView (on the bottom half) within a custom UIView (loading from another class). My objective is to have when I click on the tab bar, to move the bottom collectionView accordingly, with regards to the scrollToIndex. My issue is that when I click on the tab bar at the top, and call the function that is in my custom UIView, nothing occurs. Do I need to share information through a delegate/protocol? What am I doing incorrectly?
In my MainVC I have:
/** Setting up the top header **/
let topBar = UIView()
/** Setting up the connection to the Bottom Collection View **/
let mainView = MainViewsHome()
override func viewWillAppear(_ animated: Bool) {
self.view.layoutIfNeeded()
/**Setting up the header that the buttons lay on **/
topBar.frame = CGRect(x:self.view.frame.width * 0, y:self.view.frame.height * 0, width:self.view.frame.width,height:self.view.frame.height / 6.2)
topBar.backgroundColor = UIColor.red
self.view.addSubview(topBar)
/** Setting up the buttons in the header**/
setUpHeaderBarButtons()
/** Setting up the bottom half **/
mainView.frame = CGRect(x:self.view.frame.width * 0, y:self.view.frame.height / 6.2, width:self.view.frame.width,height:self.view.frame.height / 1.1925)
mainView.backgroundColor = UIColor.clear
self.view.addSubview(mainView)
mainView.delegate = self
}
& Then setting up the collectionView for the MainVC (the bar buttons)
func setUpHeaderBarButtons() {
let flowLayout = UICollectionViewFlowLayout()
let collectionView = UICollectionView(frame: CGRect(x: topBar.frame.width * 0, y:topBar.frame.height / 1.75, width: topBar.frame.width, height: topBar.frame.height / 3.6), collectionViewLayout: flowLayout)
collectionView.register(SelectionCVC.self, forCellWithReuseIdentifier: cellId)
collectionView.delegate = self
collectionView.dataSource = self
collectionView.backgroundColor = UIColor.clear
topBar.addSubview(collectionView)
}
&& Then the didSelect for the MainVC (The bar buttons)
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
print("selecting cell")
mainView.moveToPage()
}
&& Then my custom UIVIew with the bottom collection view that I wish to trigger a scrollToIndex
class MainViewsHome: UIView, UIGestureRecognizerDelegate, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
var cellId = "Cell"
var collectionView2 : UICollectionView!
override init(frame: CGRect) {
super.init(frame: CGRect(x:0, y:0, width:UIScreen.main.bounds.width, height: UIScreen.main.bounds.height / 1.27))
/**Creation of the View **/
let flowLayout2 : UICollectionViewFlowLayout = UICollectionViewFlowLayout()
flowLayout2.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
flowLayout2.scrollDirection = .horizontal
let collectionView2 = UICollectionView(frame: CGRect(x:self.frame.width * 0,y:self.frame.height * 0,width:self.frame.width,height: self.frame.height), collectionViewLayout: flowLayout2)
collectionView2.register(SelectionCVC.self, forCellWithReuseIdentifier: cellId)
collectionView2.isPagingEnabled = true
collectionView2.delegate = self
collectionView2.dataSource = self
collectionView2.backgroundColor = UIColor.purple
self.addSubview(collectionView2)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func moveToPage() {
// print("we are moving to page")
let indexPath = IndexPath(item: 2, section: 0) //Change section from 0 to other if you are having multiple sections
self.collectionView2?.scrollToItem(at: indexPath, at: [], animated: true)
}
}
where am i going wrong?

Answer 1

In the init of MainViewsHome instead of initializing instance property collectionView2 you are initializing completely new collectionView so you are not having reference in collectionView2.
It should be
self.collectionView2 = UICollectionView(frame: CGRect(x:self.frame.width * 0,y:self.frame.height * 0,width:self.frame.width,height: self.frame.height), collectionViewLayout: flowLayout2)
Instead of
let collectionView2 = UICollectionView(frame: CGRect(x:self.frame.width * 0,y:self.frame.height * 0,width:self.frame.width,height: self.frame.height), collectionViewLayout: flowLayout2)