UICollectionViewFlowLayout
阶级(
link to demo repo
)。中心单元格甚至在两种布局中都居中(这实际上是我问题中“奖励积分”部分的确切目的)!
这是我的视图控制器。不遵守
UICollectionViewDelegateFlowLayout
,我现在使用自定义闭包
sizeForListItemAt
和
sizeForStripItemAt
.
class ViewController: UIViewController {
var isExpanded = false
lazy var listLayout = FlowLayout(layoutType: .list)
lazy var stripLayout = FlowLayout(layoutType: .strip)
@IBOutlet weak var collectionView: UICollectionView!
@IBOutlet weak var collectionViewHeightConstraint: NSLayoutConstraint!
@IBAction func toggleExpandPressed(_ sender: Any) {
isExpanded.toggle()
if isExpanded {
collectionView.setCollectionViewLayout(listLayout, animated: true)
collectionViewHeightConstraint.constant = 300
} else {
collectionView.setCollectionViewLayout(stripLayout, animated: true)
collectionViewHeightConstraint.constant = 60
}
UIView.animate(withDuration: 0.6) {
self.view.layoutIfNeeded()
}
}
override func viewDidLoad() {
super.viewDidLoad()
collectionView.collectionViewLayout = stripLayout
collectionView.dataSource = self
/// use these instead of `UICollectionViewDelegateFlowLayout`
listLayout.sizeForListItemAt = { [weak self] indexPath in
return CGSize(width: self?.collectionView.frame.width ?? 100, height: 50)
}
stripLayout.sizeForStripItemAt = { indexPath in
return CGSize(width: 100, height: 50)
}
}
}
/// sample data source
extension ViewController: UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 10
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ID", for: indexPath)
cell.contentView.layer.borderWidth = 5
cell.contentView.layer.borderColor = UIColor.red.cgColor
return cell
}
}
UICollectionViewFlowLayout
班在…内
prepare
FlowLayout
(
listLayout
stripLayout
.).
enum LayoutType {
case list
case strip
}
class FlowLayout: UICollectionViewFlowLayout {
var layoutType: LayoutType
var sizeForListItemAt: ((IndexPath) -> CGSize)? /// get size for list item
var sizeForStripItemAt: ((IndexPath) -> CGSize)? /// get size for strip item
var layoutAttributes = [UICollectionViewLayoutAttributes]() /// store the frame of each item
var contentSize = CGSize.zero /// the scrollable content size of the collection view
override var collectionViewContentSize: CGSize { return contentSize } /// pass scrollable content size back to the collection view
override func prepare() { /// configure the cells' frames
super.prepare()
guard let collectionView = collectionView else { return }
let itemCount = collectionView.numberOfItems(inSection: 0) /// I only have 1 section
if layoutType == .list {
var y: CGFloat = 0 /// y position of each cell, start at 0
for itemIndex in 0..<itemCount {
let indexPath = IndexPath(item: itemIndex, section: 0)
let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
attributes.frame = CGRect(
x: 0,
y: y,
width: sizeForListItemAt?(indexPath).width ?? 0,
height: sizeForListItemAt?(indexPath).height ?? 0
)
layoutAttributes.append(attributes)
y += attributes.frame.height /// add height to y position, so next cell becomes offset
} /// use first item's width
contentSize = CGSize(width: sizeForStripItemAt?(IndexPath(item: 0, section: 0)).width ?? 0, height: y)
} else {
var x: CGFloat = 0 /// z position of each cell, start at 0
for itemIndex in 0..<itemCount {
let indexPath = IndexPath(item: itemIndex, section: 0)
let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
attributes.frame = CGRect(
x: x,
y: 0,
width: sizeForStripItemAt?(indexPath).width ?? 0,
height: sizeForStripItemAt?(indexPath).height ?? 0
)
layoutAttributes.append(attributes)
x += attributes.frame.width /// add width to z position, so next cell becomes offset
} /// use first item's height
contentSize = CGSize(width: x, height: sizeForStripItemAt?(IndexPath(item: 0, section: 0)).height ?? 0)
}
}
/// pass attributes to the collection view flow layout
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
return layoutAttributes[indexPath.item]
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
return layoutAttributes.filter { rect.intersects($0.frame) }
}
/// initialize with a layout
init(layoutType: LayoutType) {
self.layoutType = layoutType
super.init()
}
/// boilerplate code
required init?(coder aDecoder: NSCoder) { fatalError("init(coder:) has not been implemented") }
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool { return true }
override func invalidationContext(forBoundsChange newBounds: CGRect) -> UICollectionViewLayoutInvalidationContext {
let context = super.invalidationContext(forBoundsChange: newBounds) as! UICollectionViewFlowLayoutInvalidationContext
context.invalidateFlowLayoutDelegateMetrics = newBounds.size != collectionView?.bounds.size
return context
}
}
幸亏
this amazing article
谢谢你的大力帮助。
