Swift 3 Carousel view

CarouselView.swift

//
// Author: Robert Dimitrov
//
// License: MIT
//

import UIKit

//MARK: - CarouselViewDelegate protocol

// Carousel view delegate, responsible for displayed pages and their count
public protocol CarouselViewDelegate: class {
    
    // Returns a view for the given page
    func carouselView(carouselView: CarouselView, viewFor Page: Int) -> UIView
    
    // Returns the number of pages carousel has
    func numberOfPagesInCarouselView(carouselView: CarouselView) -> Int
    
    // Notify the delegate about a tap gesture
    func carouselView(carouselView: CarouselView, didTap page: Int)
    
}

//MARK: - CarouselView class

// Carousel scrollable view used for displaying custom page views
public class CarouselView: UIView {

    weak var delegate: CarouselViewDelegate? {
        didSet {
            reloadData()
        }
    }
    @IBOutlet weak var scrollView: UIScrollView?
    @IBOutlet weak var pageControl: UIPageControl?
    @IBOutlet weak var separator: UIView?
    weak var tapGestureRecognizer: UITapGestureRecognizer?
    
    var views: [UIView] = []
    
    var numberOfPages: Int = 0
    var currentPage: Int {
        get {
            return pageControl?.currentPage ?? 0
        }
        set {
            setCurrentPage(newValue, animated: false)
        }
    }
    
    public override func awakeFromNib() {
        super.awakeFromNib()
        
        // Setup scroll view
        scrollView?.pagingEnabled = true
        scrollView?.alwaysBounceVertical = false
        scrollView?.showsVerticalScrollIndicator = false
        scrollView?.showsHorizontalScrollIndicator = false
        
        // Setup page conrol
        pageControl?.hidesForSinglePage = true
        
        let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(tapGesture(_:)))
        tapGestureRecognizer.cancelsTouchesInView = false
        scrollView?.addGestureRecognizer(tapGestureRecognizer)
        self.tapGestureRecognizer = tapGestureRecognizer
    }
    
    func tapGesture(sender: UITapGestureRecognizer) {
        let point = sender.locationInView(scrollView)
        let page = Int(point.x / bounds.width)
        
        delegate?.carouselView(self, didTap: page)
    }
    
    func setCurrentPage(page: Int, animated: Bool) {
        scrollToPage(page, animated: animated)
        pageControl?.currentPage = page
    }
    
    func scrollToPage(page: Int, animated: Bool) {
        scrollView?.setContentOffset(CGPoint(x: CGFloat(page) * bounds.width, y: 0), animated: animated)
    }
    
    @IBAction func changePage(sender: UIPageControl) {
        setCurrentPage(sender.currentPage, animated: true)
    }
    
    public class func createCarouselView() -> CarouselView? {
        let items: [AnyObject] = NSBundle(forClass: CarouselView.self).loadNibNamed("CarouselView", owner: self, options: nil) ?? []
        
        for item: AnyObject in items {
            if let view = item as? CarouselView {
                return view
            }
        }
        
        return nil
    }
    
    public func reloadData() {
        // remove existing subviews
        for view in views {
            view.removeFromSuperview()
        }
        
        views.removeAll()
        
        // Get new data and setup elements
        numberOfPages = delegate?.numberOfPagesInCarouselView(self) ?? 0
        pageControl?.numberOfPages = numberOfPages
        pageControl?.currentPage = currentPage
        
        scrollView?.contentSize = CGSize(width: bounds.width * CGFloat(numberOfPages), height: 0)
        
        // Get relevant pages
        if let scrollView = scrollView {
            scrollViewDidScroll(scrollView)
        }
        
        // Move to beginning
        setCurrentPage(0, animated: false)
    }
    
    private func frameFor(page: Int) -> CGRect {
        return CGRect(x: CGFloat(page) * bounds.width,
                      y: 0,
                      width: bounds.width,
                      height: bounds.height)
    }
    
    private func loadView(for page: Int) {
        guard page >= 0 && page < numberOfPages else {
            return
        }
        
        // Already exists, return
        if views.count > page {
            return
        }
        
        // New page, add to scrollView and views array
        if let view = delegate?.carouselView(self, viewFor: page) {
            view.frame = frameFor(page)
            views.append(view)
            scrollView?.addSubview(view)
        }
    }

}

//MARK: - UIScrollViewDelegate

extension CarouselView: UIScrollViewDelegate {
    
    public func scrollViewDidScroll(scrollView: UIScrollView) {
        // Calculate current page
        let page = Int(scrollView.contentOffset.x / scrollView.bounds.width)
        
        // Load previous, current and next pages
        loadView(for: page - 1)
        loadView(for: page)
        loadView(for: page + 1)
    }
    
    public func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
        // Calculate current page
        let page = Int(scrollView.contentOffset.x / scrollView.bounds.width)
        
        pageControl?.currentPage = page
    }
    
}