我正在尝试使用UICollectionView而不是UITableView来显示大量项目(> 15000),并且似乎UICollectionView为集合所需的整个contentView大小预分配了像素缓冲区。根据项目的大小,模拟器最多显示所需的6.75GB内存。
基于基于UITableView的协议,我希望收集视图不会分配任何像素缓冲区,而仅依靠单元格的支持/渲染。
我正在使用情节提要文件来定义集合视图和单元格,两者均具有Opaque = false。我看过许多有关Stack Overflow的文章,其中大部分与内存泄漏有关,因此我对如何解决该问题有些困惑。
出于好奇,这里是整个代码库(故事板除外):
MyCollectionViewCell.swift
import UIKit
class MyCollectionViewCell: UICollectionViewCell {
static let identifier = "myCellIdentifier"
}
UIColor + Random.swift
import UIKit
extension UIColor {
static func randomColor() -> UIColor {
let red = CGFloat(drand48())
let green = CGFloat(drand48())
let blue = CGFloat(drand48())
return UIColor(red: red, green: green, blue: blue, alpha: 1.0)
}
}
ViewController.swift
import UIKit
class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 10000
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 30000
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MyCollectionViewCell.identifier, for: indexPath) as! MyCollectionViewCell
cell.backgroundColor = UIColor.randomColor()
return cell
}
@IBOutlet weak var collectionView: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
}
答案 0 :(得分:1)
UICollectionView适合于管理数量有限的部分。使用大量的节和项总是会导致使用大量内存,因为UIKit试图跟踪节中每个元素的位置以适当缩放contentView。
相反,创建一个自定义UICollectionViewLayout来管理大量项目之间的关系,在这些项目中应放置这些项目并与UICollectionViewDataSource进行协调,以将相对较小的项目集作为“窗口”映射到更大的项目集。
例如,假设UICollectionView项目是关于100x100的问题; UIKit将一次在屏幕上渲染大约80〜100。假设UICollectionView在用户滚动时在所有侧面都缓存了一些条目,那么在“缓存”中有1024个项目可以轮流浏览就足够了。 UICollectionView完全可以管理1个具有1024个项目的部分。
接下来,使用自定义UICollectionViewLayout定义一个自定义的contentViewSize,其大小足以容纳所有项目。 UICollectionView将通过layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]?
确保每次查询集合视图时都返回一组新的项目。使用1024个项目缓存,以屏幕上显示的第一个元素的项目索引0开始,以1表示第二个元素,以2表示第3个元素,依此类推。每次将布局中的坐标与项目索引相关联时,与UICollectionViewDataSource进行协调,以通知数据有关应该与相关索引相关联的真实部分/项目的来源。
首先,让我们定义一个协议和数据源,以将大型数据源的真实大小映射到合理的UICollectionView可以处理的事情。
LargeDataSourceCoordinator.swift:
import UIKit
protocol LargeDataSourceProtocol {
func largeNumberOfSections() -> Int
func largeNumberOfItems(in section: Int) -> Int
func largeNumberToCollectionViewCacheSize() -> Int
func associateLargeIndexPath(_ largeIndexPath: IndexPath) -> IndexPath
}
class LargeDataSourceCoordinator: NSObject, UICollectionViewDataSource, LargeDataSourceProtocol {
var cachedMapEntries: [IndexPath: IndexPath] = [:]
var rotatingCacheIndex: Int = 0
func largeNumberToCollectionViewCacheSize() -> Int {
return 1024 // arbitrary number, increase if rendering issues are visible like cells not appearing when scrolling
}
func largeNumberOfSections() -> Int {
// To do: implement logic to find the number of sections
return 10000 // simplified arbitrary number for sake of demo
}
func largeNumberOfItems(in section: Int) -> Int {
// To do: implement logic to find the number of items in each section
return 30000 // simplified arbitrary number for sake of demo
}
func associateLargeIndexPath(_ largeIndexPath: IndexPath) -> IndexPath {
for existingPath in cachedMapEntries where existingPath.value == largeIndexPath {
return existingPath.key
}
let collectionViewIndexPath = IndexPath(item: rotatingCacheIndex, section: 0)
cachedMapEntries[collectionViewIndexPath] = largeIndexPath
rotatingCacheIndex = (rotatingCacheIndex + 1) % self.largeNumberToCollectionViewCacheSize()
return collectionViewIndexPath
}
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return self.largeNumberToCollectionViewCacheSize()
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = MyCollectionViewCell.dequeue(from: collectionView, for: indexPath)
guard let largeIndexPath = cachedMapEntries[indexPath] else { return cell }
// retrieve the data at largeIndexPath.section, largeIndexPath.item
// configure cell accordingly
cell.addDebugText("section: \(largeIndexPath.section)\nitem: \(largeIndexPath.item)")
return cell
}
}
接下来,让我们创建UICollectionViewLayout来帮助定位和协调数据源。为简单起见,单元格使用固定大小为100x100的单元格,每节紧随其后显示,每个单元格紧紧排在每行的左侧。
LargeDataSourceLayout.swift:
import UIKit
class LargeDataSourceLayout: UICollectionViewLayout {
let cellSize = CGSize(width: 100, height: 100)
var cellsPerRow: CGFloat {
guard let collectionView = self.collectionView else { return 1.0 }
return (collectionView.frame.size.width / cellSize.width).rounded(.towardZero)
}
var cacheNumberOfItems: [Int] = []
private func refreshNumberOfItemsCache() {
guard
let largeDataSource = self.collectionView?.dataSource as? LargeDataSourceProtocol
else { return }
cacheNumberOfItems.removeAll()
for section in 0 ..< largeDataSource.largeNumberOfSections() {
let itemsInSection: Int = largeDataSource.largeNumberOfItems(in: section)
cacheNumberOfItems.append(itemsInSection)
}
}
var cacheRowsPerSection: [Int] = []
private func refreshRowsPerSection() {
let itemsPerRow = Float(self.cellsPerRow)
cacheRowsPerSection.removeAll()
for section in 0 ..< cacheNumberOfItems.count {
let numberOfItems = Float(cacheNumberOfItems[section])
let numberOfRows = (numberOfItems / itemsPerRow).rounded(.awayFromZero)
cacheRowsPerSection.append(Int(numberOfRows))
}
}
override var collectionViewContentSize: CGSize {
// To do: update logic as per your requirements
refreshNumberOfItemsCache()
refreshRowsPerSection()
let totalRows = cacheRowsPerSection.reduce(0, +)
return CGSize(width: self.cellsPerRow * cellSize.width,
height: CGFloat(totalRows) * cellSize.height)
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
// To do: implement logic to compute the attributes for a specific item
return nil
}
private func originForRow(_ row: Int) -> CGFloat {
return CGFloat(row) * cellSize.height
}
private func pathsInRow(_ row: Int) -> [IndexPath] {
let itemsPerRow = Int(self.cellsPerRow)
var subRowIndex = row
for section in 0 ..< cacheRowsPerSection.count {
let rowsInSection = cacheRowsPerSection[section]
if subRowIndex < rowsInSection {
let firstItem = subRowIndex * itemsPerRow
let lastItem = min(cacheNumberOfItems[section],firstItem+itemsPerRow) - 1
var paths: [IndexPath] = []
for item in firstItem ... lastItem {
paths.append(IndexPath(item: item, section: section))
}
return paths
} else {
guard rowsInSection <= subRowIndex else { return [] }
subRowIndex -= rowsInSection
}
}
// if caches are properly updated, we should never reach here
return []
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
guard let largeDataSource = self.collectionView?.dataSource as? LargeDataSourceProtocol else { return nil }
let firstRow = max(0,Int((rect.minY / cellSize.height).rounded(.towardZero)))
var row = firstRow
var attributes: [UICollectionViewLayoutAttributes] = []
repeat {
let originY = originForRow(row)
if originY > rect.maxY {
return attributes
}
var originX: CGFloat = 0.0
for largeIndexPath in pathsInRow(row) {
let indexPath = largeDataSource.associateLargeIndexPath(largeIndexPath)
let itemAttribute = UICollectionViewLayoutAttributes(forCellWith: indexPath)
itemAttribute.frame = CGRect(x: originX, y: originY, width: cellSize.width, height: cellSize.height)
attributes.append(itemAttribute)
originX += cellSize.width
}
row += 1
} while true
}
}
那里发生了一些事情,并且有很多根据用例进行优化的空间,但是这里有概念。为了完整起见,下面是相关的代码和应用预览。
MyCollectionViewCell.swift:
import UIKit
class MyCollectionViewCell: UICollectionViewCell {
static let identifier = "MyCollectionViewCell"
static func dequeue(from collectionView: UICollectionView, for indexPath: IndexPath) -> MyCollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: identifier, for: indexPath) as? MyCollectionViewCell ?? MyCollectionViewCell()
cell.contentView.backgroundColor = UIColor.random()
return cell
}
override func prepareForReuse() {
super.prepareForReuse()
removeDebugLabel()
}
private func removeDebugLabel() {
self.contentView.subviews.first?.removeFromSuperview()
}
func addDebugText(_ text: String) {
removeDebugLabel()
let debugLabel = UILabel(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
debugLabel.text = text
debugLabel.numberOfLines = 2
debugLabel.font = UIFont.systemFont(ofSize: UIFont.smallSystemFontSize)
debugLabel.textColor = UIColor.black
debugLabel.textAlignment = .center
self.contentView.addSubview(debugLabel)
}
}
UIColor + random.swift:
import UIKit
extension UIColor {
static func random() -> UIColor {
//random color
let hue = CGFloat(arc4random() % 256) / 256.0
let saturation = (CGFloat(arc4random() % 128) / 256.0) + 0.5 // 0.5 to 1.0, away from white
let brightness = (CGFloat(arc4random() % 128) / 256.0 ) + 0.5 // 0.5 to 1.0, away from black
return UIColor(hue: hue, saturation: saturation, brightness: brightness, alpha: 1.0)
}
}