Swift实现视图拉伸效果

头部视图拉伸效果

• 1.创建ViewController，懒加载collectionView

    // MARK: - 懒加载collectionView
    private lazy var collectionView : UICollectionView = {

let rect = CGRectMake(0, 0, ScreenRect.width, ScreenRect.height)
// 自定义flowLayout
let flowLayout = WYCollectionViewFlowLayout()
let collectionView = UICollectionView(frame: rect, collectionViewLayout: flowLayout

        // 设置数据源

        collectionView.dataSource = self
// 注册
        collectionView.registerClass(UICollectionViewCell.self, forCellWithReuseIdentifier: CellID)
        collectionView.registerClass(WYHeadView.self, forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, withReuseIdentifier: HeadID)

return collectionView
    }()

• 2.实现UICollectionView的数据源方法

// MARK: - 数据源方法
extension ViewController : UICollectionViewDataSource{

    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {

        return 15
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(CellID, forIndexPath: indexPath)

        cell.backgroundColor = UIColor.grayColor()
        return cell
    }

    func collectionView(collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionReusableView {

        let headView = collectionView.dequeueReusableSupplementaryViewOfKind(kind, withReuseIdentifier: HeadID, forIndexPath: indexPath) as! WYHeadView
        headView.imgName = "01.jpg"

        return headView

    }
}

• 3.自定义flowLayout

 override func prepareLayout() {
        super.prepareLayout()

        headerReferenceSize = CGSizeMake(ScreenRect.width,300)
        itemSize = CGSizeMake(ScreenRect.width,40)
    }

    override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
        return true
    }
    override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {

        // 获取可见范围内的Elements
        let attributes = super.layoutAttributesForElementsInRect(rect)

        let offset = self.collectionView?.contentOffset
        if offset?.y < 0 { // 用户向下拉

            let deltay = fabs((offset?.y)!)

            for attr in attributes!{

                let kind = attr.representedElementKind
                if kind == UICollectionElementKindSectionHeader{
                    // 获取headView的frame
                    var rect = attr.frame
                    // 改变headView的高度，y值
                    rect.size.height += deltay
                    rect.origin.y -= deltay

                    attr.frame = rect

                }

            }
        }
        return attributes
    }

• 4.自定义HeadView

    var imgName : String?{

        didSet{
            imageView.image = UIImage(named: imgName!)
        }
    }
    override init(frame: CGRect) {
        super.init(frame: frame)

        setUpUI()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func setUpUI(){

        addSubview(imageView)
        imageView.backgroundColor = UIColor.yellowColor()
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        imageView.frame = self.bounds
    }
    private lazy var imageView : UIImageView = UIImageView()

}

效果图：