Segmented control to switch collection views - ios

Question

Unable to load viewControllers.
There is no initial selection in segmented controller
when my view loads I want my firstCVC be by default the first viewController
Here is my parent viewController
class covidVC: UIViewController {
private let segmentedController: UISegmentedControl = {
let labelArr = ["Covid19","Symptoms","WHO","Vaccine"]
let seg = UISegmentedControl(items: labelArr)
seg.translatesAutoresizingMaskIntoConstraints = false
seg.tintColor = .gray
seg.addTarget(self, action:#selector(segAction(_:)), for: .valueChanged)
return seg
}()
func viewLoader(){
addChild(FirstCVC())
addChild(SecondCVC())
addChild(ThirdCVC())
addChild(FourthCVC())
self.view.addSubview(FirstCVC().view)
self.view.addSubview(SecondCVC().view)
self.view.addSubview(ThirdCVC().view)
self.view.addSubview(FourthCVC().view)
FirstCVC().didMove(toParent: self)
SecondCVC().didMove(toParent: self)
ThirdCVC().didMove(toParent: self)
FourthCVC().didMove(toParent: self)
FirstCVC().view.frame = self.view.bounds
SecondCVC().view.frame = self.view.bounds
ThirdCVC().view.frame = self.view.bounds
FourthCVC().view.frame = self.view.bounds
}
#objc func segAction(_ segmentedControll: UISegmentedControl){
FirstCVC().view.isHidden = true
SecondCVC().view.isHidden = true
ThirdCVC().view.isHidden = true
FourthCVC().view.isHidden = true
switch segmentedControll.selectedSegmentIndex {
case 0:
FirstCVC().view.isHidden = false
case 1:
SecondCVC().view.isHidden = false
case 2:
ThirdCVC().view.isHidden = false
case 3:
FourthCVC().view.isHidden = false
default:
FirstCVC().view.isHidden = false
}
}
override func viewDidLayoutSubviews() {
view.addSubview(segmentedController)
segmentedController.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
segmentedController.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor).isActive = true
}
override func viewDidLoad() {
super.viewDidLoad()
viewLoader()
}
}
All four Child view are collection VC. I want them to be independent VCs
I don't want to relaod collection views as they have different rows & cols
class FirstCVC: UIViewController, UICollectionViewDelegateFlowLayout, UICollectionViewDataSource, UICollectionViewDelegate{
// primary horizantal scrollVIew
private let myCollectionView: UICollectionView = {
let layout = UICollectionViewFlowLayout()
layout.scrollDirection = .vertical
layout.itemSize = CGSize(width: 365 , height: 300)
layout.sectionInset = UIEdgeInsets(top: 10, left: 5, bottom: 10, right: 5)
let view = UICollectionView(frame: .zero, collectionViewLayout:layout)
view.showsVerticalScrollIndicator = false
view.translatesAutoresizingMaskIntoConstraints = false
view.backgroundColor = .red
return view
}()
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 3
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "FirstCustomCell", for: indexPath) as! FirstCustomCell
cell.backgroundColor = .red
return cell
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
view.addSubview(myCollectionView)
myCollectionView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor).isActive = true
myCollectionView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true
myCollectionView.widthAnchor.constraint(equalTo: view.safeAreaLayoutGuide.widthAnchor).isActive = true
}
override func viewDidLoad() {
super.viewDidLoad()
myCollectionView.dataSource = self
myCollectionView.delegate = self
myCollectionView.register(FirstCustomCell.self, forCellWithReuseIdentifier: FirstCustomCell.identifier)
}
}
The Image output I'm getting

Answer 1

You create a different instance each line
addChild(FirstCVC())
addChild(SecondCVC())
addChild(ThirdCVC())
addChild(FourthCVC())
self.view.addSubview(FirstCVC().view)
self.view.addSubview(SecondCVC().view)
self.view.addSubview(ThirdCVC().view)
self.view.addSubview(FourthCVC().view)
FirstCVC().didMove(toParent: self)
SecondCVC().didMove(toParent: self)
ThirdCVC().didMove(toParent: self)
FourthCVC().didMove(toParent: self)
FirstCVC().view.frame = self.view.bounds
SecondCVC().view.frame = self.view.bounds
ThirdCVC().view.frame = self.view.bounds
FourthCVC().view.frame = self.view.bounds
while it should be
let vc1 = FirstCVC()
let vc2 = SecondCVC()
let vc3 = ThirdCVC()
let vc4 = FourthCVC()
addChild(vc1)
addChild(vc2)
addChild(vc3)
addChild(vc4)
self.view.addSubview(vc1.view)
self.view.addSubview(vc2.view)
self.view.addSubview(vc3.view)
self.view.addSubview(vc4.view)
vc1.didMove(toParent: self)
vc2.didMove(toParent: self)
vc3.didMove(toParent: self)
vc4.didMove(toParent: self)
vc1.view.frame = self.view.bounds
vc2.view.frame = self.view.bounds
vc3.view.frame = self.view.bounds
vc4.view.frame = self.view.bounds
Tip : Also you better create an extension instead of repeating the 4 lines for each vc