需求: 固定高度的區(qū)域, 里面左右分頁顯示多個圖標(biāo), 每頁從左往右排列, 排滿后從上往下排, 這一頁排滿后排下一頁.參照oc的實(shí)現(xiàn)方式

如圖所示

我們很容易想到利用UICollectionView來實(shí)現(xiàn), 設(shè)置UICollectionViewFlowLayout, 然后設(shè)置為橫向.代碼如下:

fileprivate lazy var collectionView: UICollectionView = { [unowned self] in
        let layout = UICollectionViewFlowLayout()
        layout.minimumLineSpacing = 0
        layout.minimumInteritemSpacing = 0
//        layout.rowCount = 2
//        layout.itemCountPerRow = 3
        layout.itemSize = CGSize(width: self.zs_width / 3.0, height: self.zs_width / 3.0 + 60.0)
        layout.scrollDirection = .horizontal
        
        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collectionView.frame = CGRect(x: 0, y: 0, width: self.zs_width, height: self.zs_height - 20.0)
        collectionView.showsVerticalScrollIndicator = false
        collectionView.showsHorizontalScrollIndicator = false
        collectionView.delegate = self
        collectionView.dataSource = self
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "CELLID")
        collectionView.isPagingEnabled = true
        return collectionView
    }()

這段代碼實(shí)現(xiàn)的效果:

p2

怎么實(shí)現(xiàn)上述效果呢?

1. 可以用大cell包含5個小圖標(biāo)來實(shí)現(xiàn)(這樣就比較復(fù)雜)
2. 重寫UICollectionViewFlowLayout

這里我用重寫UICollectionViewFlowLayout實(shí)現(xiàn)

思路: 獲取collectionView所有cell的屬性, 然后進(jìn)行indexpath的計(jì)算, 用新計(jì)算出的indexPath替換原有的indexPath.

1.聲明屬性

    /** 一行中cell的個數(shù)*/
    public var itemCountPerRow: Int!
    /** 一頁顯示多少行*/
    public var rowCount: Int!
    /** 存儲collectionView上cell的屬性*/
    fileprivate var allAttributes: [UICollectionViewLayoutAttributes] = []

2.獲取所有cell的屬性

    override func prepare() {
        super.prepare()
        let count = self.collectionView?.numberOfItems(inSection: 0) ?? 0
        for i in 0..<count {
            let indexPath = NSIndexPath(item: i, section: 0)
            let attributes = self.layoutAttributesForItem(at: indexPath as IndexPath)
            allAttributes.append(attributes!)
        }
    }

3.交換indexPath

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        var item = indexPath.item
        
        var x = 0
        var y = 0
        self.targetPosition(item: item, x: &x, y: &y)
        item = originItem(x, y: y)
        let newIndexPath = NSIndexPath(item: item, section: 0)
        let theNewAttr = super.layoutAttributesForItem(at: newIndexPath as IndexPath)
        theNewAttr?.indexPath = indexPath
        return theNewAttr
    }
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        let attributes = super.layoutAttributesForElements(in: rect)
        var tmp: [UICollectionViewLayoutAttributes] = []
        for attr in attributes! {
            for attr2 in self.allAttributes {
                if attr.indexPath.item == attr2.indexPath.item {
                    tmp.append(attr2)
                    break
                }
            }
        }
        return tmp
    }
    //根據(jù)item計(jì)算出目標(biāo)item的偏移量
    //x 橫向偏移 y 豎向偏移
    fileprivate func targetPosition(item: Int, x: inout Int, y: inout Int) {
        let page = item / (self.itemCountPerRow * self.rowCount)
        
        x = item % self.itemCountPerRow + page * self.itemCountPerRow
        y = item / self.itemCountPerRow - page * self.rowCount
        
    }
    //根據(jù)偏移量計(jì)算item
    fileprivate func originItem(_ x: Int, y: Int) -> Int {
        let item = x * self.rowCount + y
        return item
    }