BannerView-2.swift

import UIKit

class BannerView: UIView {
   
   private let scrollView:UIScrollView = {
        let sc = UIScrollView(frame: .zero)
        sc.translatesAutoresizingMaskIntoConstraints = false
        sc.isPagingEnabled = true
        return sc
    }()
   
   // BannerView DataSources (1)
   private var itemAtIndex:((_ bannerView:BannerView , _ index:Int)->(UIView))!
   private var numberOfItems:Int = 0
   
   override init(frame: CGRect) {
        super.init(frame: frame)
        setUpUI()
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
     private func setUpUI() {
        scrollView.frame = CGRect(x: 0, y: 0, width: self.frame.size.width, height: self.frame.size.height)
        scrollView.delegate = self
        self.addSubview(scrollView)
        scrollView.showsHorizontalScrollIndicator = false
    }
    
     func reloadData(numberOfItems:Int , itemAtIndex:@escaping ((_ bannerView:BannerView , _ index:Int)->(UIView)) ) {
       self.itemAtIndex = itemAtIndex
        self.numberOfItems = numberOfItems
       reloadScrollView()
    }
    
    private func reloadScrollView() {
        guard self.numberOfItems > 0 else { return }
        if self.numberOfItems == 1 {
            let firstItem:UIView = self.itemAtIndex(self , 0)
            addViewToIndex(view: firstItem, index: 0)
            scrollView.isScrollEnabled = false 
            return
        }
        let firstItem:UIView = self.itemAtIndex(self , 0)
        addViewToIndex(view: firstItem, index: numberOfItems+1)
        
        let lastItem:UIView = self.itemAtIndex(self , numberOfItems-1)
        addViewToIndex(view: lastItem, index: 0)
        for index in 0..<self.numberOfItems {
            let item:UIView = self.itemAtIndex(self , index)
            addViewToIndex(view: item, index: index+1)
        }
        scrollView.contentSize = CGSize(width: CGFloat(numberOfItems+2)*scrollView.frame.size.width, height: scrollView.frame.size.height)
        scrollView.contentOffset = CGPoint(x: self.scrollView.frame.size.width, y: self.scrollView.contentOffset.y)
    }
    
    private func addViewToIndex(view:UIView, index:Int) {
        view.translatesAutoresizingMaskIntoConstraints = false
        scrollView.addSubview(view)
        view.frame = CGRect(x: CGFloat(index)*scrollView.frame.size.width, y: 0, width: scrollView.frame.size.width, height: scrollView.frame.size.height)
    }
    
 }