Infinite-LoopView

InfiniteLoopView.swift

import UIKit

final class InfiniteLoopView<T, Cell>: UIView,
UICollectionViewDelegate,
UICollectionViewDataSource,
UICollectionViewDelegateFlowLayout
where Cell: UICollectionViewCell {

    private lazy var collectionView: UICollectionView = {
        let collectionViewLayout = UICollectionViewFlowLayout()
        collectionViewLayout.scrollDirection = .horizontal
        collectionViewLayout.minimumLineSpacing = 0
        
        let view = UICollectionView(frame: .zero, collectionViewLayout: collectionViewLayout)
        view.backgroundColor = .clear
        view.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
        view.register(Cell.self,
                      forCellWithReuseIdentifier: String(describing: Cell.self))
        view.delegate = self
        view.dataSource = self
        view.showsVerticalScrollIndicator = false
        view.showsHorizontalScrollIndicator = false
        view.isPagingEnabled = true
        
        return view
    }()
    
    // MARK: data source
    /// 輪播畫面
    var inputDatas = [T]() { didSet { dataSourceDidChange() } }
    
    /// 輪播秒數
    var changeSec: Int? = nil { didSet { restartTimer() } }
    
    /// 設置外部 page viewControl (numberOfPages, currentPage)
    var pageIndexHandler: ((Int, Int) -> Void)?
    
    /// 設置 cell 和 資料型別
    var configure: (T, Cell) -> Void
    
    /// 點擊 cell 觸發事件
    var selectHandler: ((Int) -> Void)?
    
    private var currentPage = Int()
    private var collectionInputDatas = [T]()
    private var timer: Timer?
    private let itemSize: CGSize
    
    // Life cycle
    init(itemSize: CGSize, configure: @escaping (T, Cell) -> Void) {
        
        self.itemSize = itemSize
        self.configure = configure
        
        super.init(frame: .zero)
        
        setupUI()
    }
    
    required init?(coder aDecoder: NSCoder) { fatalError() }
    
    deinit { cleanTimer() }
    
    // MARK: Helper Method
    
    private func dataSourceDidChange() {
        guard
            let firstItem = inputDatas.first,
            let lastItem = inputDatas.last
        else {
                return
        }
        
        collectionInputDatas = [lastItem] + inputDatas + [firstItem]
        
        UIView.animate(withDuration: 0, animations: {
            self.collectionView.reloadData()
        }) { _ in
            self.collectionView.setContentOffset(CGPoint(x: UIScreen.main.bounds.width, y: 0), animated: false)
            self.pageIndexHandler?(self.inputDatas.count, 0)
            self.collectionView.isScrollEnabled = self.inputDatas.count != 1
        }
    }
    
    private func startTimer() {
        
        guard let changeSec = changeSec else { return }
        
        timer = Timer.scheduledTimer(
            timeInterval: TimeInterval(changeSec),
            target: self,
            selector: #selector(scrollToNext),
            userInfo: nil,
            repeats: true
        )
    }
    
    private func cleanTimer() {
        
        timer?.invalidate()
        timer = nil
    }
    
    private func restartTimer() {
        
        cleanTimer()
        startTimer()
    }
    
    @objc private func scrollToNext() {
        
        if !(collectionView.isScrollEnabled) {
            return
        }
        
        let x = CGFloat(Int(UIScreen.main.bounds.width) * (currentPage + 1))
        collectionView.setContentOffset(CGPoint(x: x, y: 0), animated: true)
    }
    
    @objc private func scroll(to index: Int) {
        
        if index == 0 { // 滑到 index 0 時, 把 index 改成 last
            let x = CGFloat(Int(UIScreen.main.bounds.width) * (collectionInputDatas.count - 2))
            collectionView.setContentOffset(CGPoint(x: x, y: 0), animated: false)
        } else if index == collectionInputDatas.count - 1 { // 滑到 last index 時, 把 index 改成 1
            let x = UIScreen.main.bounds.width
            collectionView.setContentOffset(CGPoint(x: x, y: 0), animated: false)
        }
        
        let setIndxe = Int(collectionView.contentOffset.x / UIScreen.main.bounds.width)
        pageIndexHandler?(inputDatas.count, setIndxe - 1)
        currentPage = setIndxe
    }
    
    // MARK: - UICollectionViewDelegate
    
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        
        if scrollView.frame.size.width <= 0 {
            return
        }
        // 原始資料
        let pageFloat = (scrollView.contentOffset.x / scrollView.frame.size.width)
        
        // 無條件捨去
        let pageInt = Int(pageFloat)
        
        // 無條件進位
        let pageCeil = Int(ceil(pageFloat))
        
        if pageInt == 0 {
            scroll(to: pageCeil)
        } else {
            scroll(to: pageInt)
        }
    }
    
    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        cleanTimer()
    }
    
    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        startTimer()
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        var index = indexPath.row - 1
        index = max(-1, index)
        index = min(index, inputDatas.count - 1)
        selectHandler?(index)
    }
    
    // MARK: - UICollectionViewDataSource
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return collectionInputDatas.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        guard
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: String(describing: Cell.self), for: indexPath) as? Cell
        else {
            return UICollectionViewCell()
        }
        let item = collectionInputDatas[indexPath.row]
        configure(item, cell)
        return cell
    }
    
    // MARK: - UICollectionViewDelegateFlowLayout
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return itemSize
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        return UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
    }
    
    // MARK: - Setup UI
    
    private func setupUI() {
        
        backgroundColor = .clear
        
        addSubview(collectionView)
        
        NSLayoutConstraint.activate([
            collectionView.leadingAnchor.constraint(equalTo: leadingAnchor),
            collectionView.topAnchor.constraint(equalTo: topAnchor),
            collectionView.trailingAnchor.constraint(equalTo: trailingAnchor),
            collectionView.bottomAnchor.constraint(equalTo: bottomAnchor),
            collectionView.heightAnchor.constraint(equalToConstant: itemSize.height),
            collectionView.widthAnchor.constraint(equalToConstant: itemSize.width)
        ])
    }
}