我的问题是 UITableView 在滚动时滞后很多。
This is what I am trying to achieve
从顶部开始，我有一个简单的节标题，其中只有一个复选框和一个 UILabel。在此标题下，您可以看到一个自定义单元格，其中只有一个 UILabel 与中心对齐。此自定义单元格的工作方式类似于下面显示的数据的另一个标题(基本上是 3D 数组)。在这些“标题”下方是包含一个多行 UILabel 的自定义单元格，在此标签下方是一个容器，用于包含一个复选框和一个 UILabel 的可变行数。单元格右侧还有一个按钮(蓝色/白色箭头)。
所以这意味着内容显示如下:
- 部分标题(包含日期和日期)
- Custom UITableViewCell = header(包含一些header信息)
- 自定义 UITableViewCell(包含要显示的数据)
这是我的代码:
cellForRowAt:
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let (isHeader, headerNumber, semiResult) = checkIfIsHeader(section: indexPath.section, row: indexPath.row)
let row = indexPath.row
if isHeader {
let chod = objednavkaDny[indexPath.section].chody[headerNumber+1]
let cell = tableView.dequeueReusableCell(withIdentifier: cellHeaderReuseIdentifier, for: indexPath) as! ObjednavkyHeaderTableViewCell
cell.titleLabel.text = chod.popisPoradiJidla
cell.selectionStyle = .none
return cell
}else{
let chod = objednavkaDny[indexPath.section].chody[headerNumber]
let cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier, for: indexPath) as! ObjednavkyTableViewCell
cell.updateData(objednavka: chod.objednavky[row-semiResult], canSetAmount: self.typDialogu == 3)
return cell
}
}
checkIfIsHeader:
func checkIfIsHeader(section: Int, row: Int) -> (Bool, Int, Int){
if let cachedResult = checkIfHeaderCache[section]?[row] {
return (cachedResult[0] == 1, cachedResult[1], cachedResult[2])
}
var isHeader = false
var semiResult = 0
var headerNumber = -1
for (index, chod) in objednavkaDny[section].chody.enumerated() {
let sum = chod.objednavky.count
if row == semiResult {
isHeader = true
break
}else if row < semiResult {
semiResult -= objednavkaDny[section].chody[index-1].objednavky.count
break
}else {
headerNumber += 1
semiResult += 1
if index != objednavkaDny[section].chody.count - 1 {
semiResult += sum
}
}
}
checkIfHeaderCache[section] = [Int:[Int]]()
checkIfHeaderCache[section]![row] = [isHeader ? 1 : 0, headerNumber, semiResult]
return (isHeader, headerNumber, semiResult)
}
以及显示数据的主单元格:
class ObjednavkyTableViewCell: UITableViewCell {
lazy var numberTextField: ObjednavkyTextField = {
let textField = ObjednavkyTextField()
textField.translatesAutoresizingMaskIntoConstraints = false
return textField
}()
let mealLabel: UILabel = {
let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
label.textColor = .black
label.textAlignment = .left
label.font = UIFont(name: ".SFUIText", size: 15)
label.numberOfLines = 0
label.backgroundColor = .white
label.isOpaque = true
return label
}()
lazy var detailsButton: UIButton = {
let button = UIButton(type: .custom)
button.translatesAutoresizingMaskIntoConstraints = false
button.setImage(UIImage(named: "arrow-right")?.withRenderingMode(.alwaysTemplate), for: .normal)
button.imageView?.tintColor = UIColor.custom.blue.classicBlue
button.imageView?.contentMode = .scaleAspectFit
button.contentHorizontalAlignment = .right
button.imageEdgeInsets = UIEdgeInsetsMake(10, 0, 10, 0)
button.addTarget(self, action: #selector(detailsButtonPressed), for: .touchUpInside)
button.backgroundColor = .white
button.isOpaque = true
return button
}()
let pricesContainerView: UIView = {
let view = UIView()
view.translatesAutoresizingMaskIntoConstraints = false
view.backgroundColor = .white
view.isOpaque = true
return view
}()
var canSetAmount = false {
didSet {
canSetAmount ? showNumberTextField() : hideNumberTextField()
}
}
var shouldShowPrices = false {
didSet {
shouldShowPrices ? showPricesContainerView() : hidePricesContainerView()
}
}
var pricesContainerHeight: CGFloat = 0
private let priceViewHeight: CGFloat = 30
var mealLabelLeadingConstraint: NSLayoutConstraint?
var mealLabelBottomConstraint: NSLayoutConstraint?
var pricesContainerViewHeightConstraint: NSLayoutConstraint?
var pricesContainerViewBottomConstraint: NSLayoutConstraint?
override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
super.init(style: style, reuseIdentifier: reuseIdentifier)
self.selectionStyle = .none
setupView()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
@objc func detailsButtonPressed() {
}
func updateData(objednavka: Objednavka, canSetAmount: Bool) {
self.canSetAmount = canSetAmount
if let popisJidla = objednavka.popisJidla, popisJidla != "", popisJidla != " " {
self.mealLabel.text = popisJidla
}else{
self.mealLabel.text = objednavka.nazevJidelnicku
}
if objednavka.objects.count > 1 {
shouldShowPrices = true
setPricesStackView(with: objednavka.objects)
checkIfSelected(objects: objednavka.objects)
}else{
shouldShowPrices = false
self.numberTextField.text = String(objednavka.objects[0].pocet)
//setSelected(objednavka.objects[0].pocet > 0, animated: false)
objednavka.objects[0].pocet > 0 ? setSelectedStyle() : setDeselectedStyle()
}
}
//---------------
func checkIfSelected(objects: [ObjednavkaObject]) {
var didChangeSelection = false
for object in objects { // Checks wether cell should be selected or not
if object.pocet > 0 {
setSelected(true, animated: false)
setSelectedStyle()
didChangeSelection = true
break
}
}
if !didChangeSelection {
setSelected(false, animated: false)
setDeselectedStyle()
}
}
//--------------
func showNumberTextField() {
numberTextField.isHidden = false
mealLabelLeadingConstraint?.isActive = false
mealLabelLeadingConstraint = mealLabel.leadingAnchor.constraint(equalTo: numberTextField.trailingAnchor, constant: 10)
mealLabelLeadingConstraint?.isActive = true
}
func hideNumberTextField() {
numberTextField.isHidden = true
mealLabelLeadingConstraint?.isActive = false
mealLabelLeadingConstraint = mealLabel.leadingAnchor.constraint(equalTo: readableContentGuide.leadingAnchor, constant: 0)
mealLabelLeadingConstraint?.isActive = true
}
func showPricesContainerView() {
hideNumberTextField()
pricesContainerView.isHidden = false
mealLabelBottomConstraint?.isActive = false
pricesContainerViewBottomConstraint?.isActive = true
}
func hidePricesContainerView() {
pricesContainerView.isHidden = true
pricesContainerViewBottomConstraint?.isActive = false
mealLabelBottomConstraint?.isActive = true
}
//--------------
func setSelectedStyle() {
self.backgroundColor = UIColor.custom.blue.classicBlue
mealLabel.textColor = .white
mealLabel.backgroundColor = UIColor.custom.blue.classicBlue
for subview in pricesContainerView.subviews where subview is ObjednavkyPriceView {
let priceView = (subview as! ObjednavkyPriceView)
priceView.titleLabel.textColor = .white
priceView.checkBox.backgroundColor = UIColor.custom.blue.classicBlue
priceView.titleLabel.backgroundColor = UIColor.custom.blue.classicBlue
priceView.backgroundColor = UIColor.custom.blue.classicBlue
}
pricesContainerView.backgroundColor = UIColor.custom.blue.classicBlue
detailsButton.imageView?.tintColor = .white
detailsButton.backgroundColor = UIColor.custom.blue.classicBlue
}
func setDeselectedStyle() {
self.backgroundColor = .white
mealLabel.textColor = .black
mealLabel.backgroundColor = .white
for subview in pricesContainerView.subviews where subview is ObjednavkyPriceView {
let priceView = (subview as! ObjednavkyPriceView)
priceView.titleLabel.textColor = .black
priceView.checkBox.backgroundColor = .white
priceView.titleLabel.backgroundColor = .white
priceView.backgroundColor = .white
}
pricesContainerView.backgroundColor = .white
detailsButton.imageView?.tintColor = UIColor.custom.blue.classicBlue
detailsButton.backgroundColor = .white
}
//-----------------
func setPricesStackView(with objects: [ObjednavkaObject]) {
let subviews = pricesContainerView.subviews
var subviewsToDelete = subviews.count
for (index, object) in objects.enumerated() {
subviewsToDelete -= 1
if subviews.count - 1 >= index {
let priceView = subviews[index] as! ObjednavkyPriceView
priceView.titleLabel.text = object.popisProduktu // + " " + NSNumber(value: object.cena).getFormattedString(currencySymbol: "Kč") // TODO: currencySymbol
priceView.canSetAmount = canSetAmount
priceView.count = object.pocet
priceView.canOrder = (object.nelzeObj == nil || object.nelzeObj == "")
}else {
let priceView = ObjednavkyPriceView(frame: CGRect(x: 0, y: CGFloat(index) * priceViewHeight + CGFloat(index * 5), width: pricesContainerView.frame.width, height: priceViewHeight))
pricesContainerView.addSubview(priceView)
priceView.titleLabel.text = object.popisProduktu // + " " + NSNumber(value: object.cena).getFormattedString(currencySymbol: "Kč") // TODO: currencySymbol
priceView.numberTextField.delegate = self
priceView.canSetAmount = canSetAmount
priceView.canOrder = (object.nelzeObj == nil || object.nelzeObj == "")
priceView.count = object.pocet
pricesContainerHeight += ((index == 0) ? 30 : 35)
}
}
if subviewsToDelete > 0 { // Deletes unwanted subviews
for _ in 0..<subviewsToDelete {
pricesContainerView.subviews.last?.removeFromSuperview()
pricesContainerHeight -= pricesContainerHeight + 5
}
}
if pricesContainerHeight < 0 {
pricesContainerHeight = 0
}
pricesContainerViewHeightConstraint?.constant = pricesContainerHeight
}
func setupView() {
self.layer.shouldRasterize = true
self.layer.rasterizationScale = UIScreen.main.scale
self.backgroundColor = .white
contentView.addSubview(numberTextField)
contentView.addSubview(mealLabel)
contentView.addSubview(detailsButton)
contentView.addSubview(pricesContainerView)
setupConstraints()
}
func setupConstraints() {
numberTextField.anchor(leading: readableContentGuide.leadingAnchor, size: CGSize(width: 30, height: 30))
numberTextField.centerYAnchor.constraint(equalTo: mealLabel.centerYAnchor).isActive = true
detailsButton.anchor(trailing: readableContentGuide.trailingAnchor, size: CGSize(width: 30, height: 30))
detailsButton.centerYAnchor.constraint(equalTo: contentView.centerYAnchor).isActive = true
mealLabel.anchor(top: contentView.topAnchor, trailing: detailsButton.leadingAnchor, padding: .init(top: 10, left: 0, bottom: 0, right: -10))
mealLabelBottomConstraint = mealLabel.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -10)
mealLabelBottomConstraint?.priority = UILayoutPriority(rawValue: 999)
pricesContainerView.anchor(top: mealLabel.bottomAnchor, leading: readableContentGuide.leadingAnchor, trailing: detailsButton.leadingAnchor, padding: .init(top: 10, left: 0, bottom: 0, right: -10))
pricesContainerViewBottomConstraint = pricesContainerView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -10)
pricesContainerViewBottomConstraint?.priority = UILayoutPriority(rawValue: 999)
pricesContainerViewHeightConstraint = pricesContainerView.heightAnchor.constraint(equalToConstant: 0)
pricesContainerViewHeightConstraint?.priority = UILayoutPriority(rawValue: 999)
pricesContainerViewHeightConstraint?.isActive = true
}
}
总结一下它是如何完成的:
tableView.rowHeight设置为UITableViewAutomaticDymension- 在
cellForRowAt中，我从数组中获取数据并将其提供给 细胞 - 所有单元格都使用约束在代码中设置
- 所有 View 都设置了
isOpaque = true - 缓存单元格的高度
- 单元格设置为栅格化
我还注意到它在某些滚动级别滞后，有时它工作得很好，有时它滞后很多。
尽管我进行了所有优化，但 tableView 在滚动时仍然滞后。
Here is a screenshot from Instruments
非常感谢任何有关如何提高滚动性能的提示!
(我可能忘记包含一些代码/信息，所以请随时在评论中问我。)
最佳答案
我无法告诉您延迟发生的确切位置，但当我们谈论滚动期间的延迟时，它与您的 cellForRowAt 委托(delegate)方法有关。发生的事情是在这个方法中发生了太多事情，并且它被调用用于显示和将要显示的每个单元格。我看到您正在尝试通过 checkIfHeaderCache 缓存结果，但仍然在最开始有一个 for 循环来确定标题单元格。
建议:
我不知道你从哪里得到数据 (objednavkaDny) 但在你得到数据之后，做一个完整的循环并一个一个地确定单元格类型，并将结果保存在你的基础上设计。在此加载期间，您可以在屏幕上显示一些加载消息。然后，在 cellForRow 方法中，您应该只是简单地使用诸如
if (isHeader) {
render header cell
} else {
render other cell
}
底线:
cellForRow 方法不是为处理繁重的计算而设计的，如果这样做会减慢滚动速度。此方法仅用于将值分配给缓存的 TableView 单元格，这是它唯一擅长的事情。
关于ios - 带有自定义单元格的 UITableView 在滚动时滞后，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/50116654/