100 lines
3.0 KiB
Swift
100 lines
3.0 KiB
Swift
//
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// Copyright 2019 Signal Messenger, LLC
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// SPDX-License-Identifier: AGPL-3.0-only
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//
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import SignalCoreKit
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// A trivial layout that places each item in a horizontal line.
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// Each item has uniform size.
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class LinearHorizontalLayout: UICollectionViewLayout {
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private let itemSize: CGSize
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private let spacing: CGFloat
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private var itemAttributesMap = [UICollectionViewLayoutAttributes]()
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private var contentSize = CGSize.zero
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// MARK: Initializers and Factory Methods
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@available(*, unavailable, message: "use other constructor instead.")
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required init?(coder aDecoder: NSCoder) {
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fatalError("init(coder:) has not been implemented")
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}
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required init(itemSize: CGSize, spacing: CGFloat = 0) {
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self.itemSize = itemSize
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self.spacing = spacing
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super.init()
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}
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// MARK: Methods
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override func invalidateLayout() {
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super.invalidateLayout()
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itemAttributesMap.removeAll()
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}
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override func invalidateLayout(with context: UICollectionViewLayoutInvalidationContext) {
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super.invalidateLayout(with: context)
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itemAttributesMap.removeAll()
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}
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override func prepare() {
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super.prepare()
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guard let collectionView = collectionView else {
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return
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}
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guard collectionView.numberOfSections == 1 else {
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owsFailDebug("This layout only support a single section.")
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return
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}
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let itemCount = collectionView.numberOfItems(inSection: 0)
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guard itemCount > 0 else {
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contentSize = .zero
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return
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}
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for row in 0..<itemCount {
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// TODO: We should ultimately make this layout RTL.
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let itemX: CGFloat = CGFloat(row) * (itemSize.width + spacing)
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let itemFrame = CGRect(x: itemX, y: 0, width: itemSize.width, height: itemSize.height)
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let indexPath = NSIndexPath(row: row, section: 0)
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let itemAttributes = UICollectionViewLayoutAttributes(forCellWith: indexPath as IndexPath)
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itemAttributes.frame = itemFrame
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itemAttributesMap.append(itemAttributes)
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}
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contentSize = CGSize(width: CGFloat(itemCount) * itemSize.width + CGFloat(itemCount - 1) * spacing,
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height: itemSize.height)
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}
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override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
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return itemAttributesMap.filter { itemAttributes in
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return itemAttributes.frame.intersects(rect)
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}
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}
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override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
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return itemAttributesMap[safe: indexPath.row]
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}
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override var collectionViewContentSize: CGSize {
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return contentSize
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}
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override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
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guard let collectionView = collectionView else {
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return false
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}
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return collectionView.width != newBounds.size.width
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}
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}
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