我在这里给你看一个例子。装饰视图 S1View 是 UICollectionViewCell 的子类，标识符为“background”。
代码不难理解，但组合起来很乏味。如何控制动画师是另一回事。
class TestCollectionViewLayout: UICollectionViewLayout {
lazy var dataSource : UICollectionViewDataSource? = {
self.collectionView?.dataSource
}()
var layouts : [IndexPath: UICollectionViewLayoutAttributes?] = [:]
var itemNumber : Int {
return dataSource!.collectionView(collectionView!, numberOfItemsInSection: 0)
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]?{
var itemArray = (0..<itemNumber).map{ self.layoutAttributesForItem(at: IndexPath.init(row: $0, section: 0))!}
itemArray.append(self.layoutAttributesForDecorationView(ofKind:"background"
, at: IndexPath.init(row: 0, section: 0)))
return itemArray
}
override var collectionViewContentSize: CGSize { get{
return self.collectionView?.frame.size ?? CGSize.zero
}
}
lazy var dynamicAnimator = {UIDynamicAnimator(collectionViewLayout: self)}()
private func updateCurrentLayoutAttributesForItem(at indexPath: IndexPath, current: UICollectionViewLayoutAttributes?) -> UICollectionViewLayoutAttributes?{
return current
}
private func initLayoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes?{
let layoutAttributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
let center = (collectionView?.center)!
let angle = (CGFloat(indexPath.row) / CGFloat(itemNumber) * CGFloat.pi * 2)
layoutAttributes.center = CGPoint.init(x: center.x + cos(angle) * CGFloat(radius) , y: center.y + sin(angle) * CGFloat(radius) )
layoutAttributes.bounds = CGRect.init(x: 0, y: 0, width: 100, height: 100 )
if let decorator = self.decorator {
let itemBehavior =
UIAttachmentBehavior.pinAttachment(with: layoutAttributes, attachedTo: decorator, attachmentAnchor: layoutAttributes.center)
dynamicAnimator.addBehavior(itemBehavior)
layouts[indexPath] = layoutAttributes
}
return layoutAttributes
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes?{
guard let currentLayout = layouts[indexPath] else {
return initLayoutAttributesForItem(at:indexPath)}
return currentLayout
}
private let radius = 200
private var decorator: UICollectionViewLayoutAttributes?
override func layoutAttributesForDecorationView(ofKind elementKind: String, at indexPath: IndexPath) -> UICollectionViewLayoutAttributes{
guard let decorator = self.decorator else {
let layoutAttributes = UICollectionViewLayoutAttributes.init(forDecorationViewOfKind: elementKind, with: indexPath)
layoutAttributes.center = (self.collectionView?.center)!
layoutAttributes.bounds = CGRect.init(x: 0, y: 0, width: radius, height: radius)
self.decorator = layoutAttributes
return layoutAttributes
}
return decorator
}
lazy var s: UIDynamicItemBehavior = {
let decorator = self.decorator!
let s = UIDynamicItemBehavior.init(items: [decorator])
s.angularResistance = 1
dynamicAnimator.addBehavior(s)
return s
}()
func rotate(_ speed: CGFloat){
guard let decorator = self.decorator else {return}
s.addAngularVelocity(speed, for: decorator)
}
}
class TestCollectionViewController: UICollectionViewController {
var startLocation = CGPoint.zero
var endLocation = CGPoint.zero
@objc private func gestureReader(_ gesture: UIPanGestureRecognizer) {
let currentLocation = gesture.location(in: self.collectionView)
if gesture.state == .began {
startLocation = currentLocation
}
else if gesture.state == .ended {
endLocation = currentLocation
self.startRotatingView(start: startLocation, end: endLocation)
}
}
private func startRotatingView(start:CGPoint, end: CGPoint) {
let dx = end.x - start.x
let dy = end.y - start.y
let distance = abs(sqrt(dx*dx + dy*dy))
if start.x < end.x {
if start.y > end.y {
//positive value of pi
self.circleAnimation(-distance)
}else {
//negitive value of pi
self.circleAnimation(distance)
}
}else {
if start.y > end.y {
//positive value of pi
self.circleAnimation(-distance)
}else {
//negitive value of pi
self.circleAnimation(distance)
}
}
}
private func circleAnimation(_ angle:CGFloat) {
(collectionView.collectionViewLayout as? TestCollectionViewLayout).map{
$0.rotate(angle / 100)
}
// UIView.animate(withDuration: 0.7, delay: 0, options: .curveLinear, animations: {
// self.collectionView.transform = CGAffineTransform.identity
// self.collectionView.transform = CGAffineTransform.init(rotationAngle: angle)
// }) { (true) in
// //
// }
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
// Timer.scheduledTimer(withTimeInterval: 1.0, repeats: false) { (Timer) in
// self.rotate()
// }
}
override func viewDidLoad() {
super.viewDidLoad()
collectionView.collectionViewLayout = TestCollectionViewLayout()
collectionView.collectionViewLayout.register(UINib.init(nibName: "S1View", bundle: nil) , forDecorationViewOfKind: "background")
let panGesture = UIPanGestureRecognizer(target: self, action: #selector(self.gestureReader(_:)))
panGesture.cancelsTouchesInView = false
self.collectionView.addGestureRecognizer(panGesture)
}
var data: [Int] = [1,2,3,4,5,6,7]
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return data.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath)
return cell
}
}