自从升级到iOS 9以来，一直运行良好的代码开始在滚动时显示出非常糟糕的性能。
我尝试从头开始创建一个最小的示例，省略了大部分单元格的配置以及各种缓存和内容生成代码。然而，代码仍然不是快速阅读，并且分析显示不同：/
根据Apple开发者论坛（编辑：我找到了link），这可能是由于自动布局的变化以及后面布局重视的结果superView使它不那么糟糕，仍然不够好发布。
我怀疑问题在于UIKit，特别是在自动布局和UITextView中，因为一旦我开始设置cell.textView.text，滚动就会立即变得粗糙。
是否有人提出类似意见？对于许多人来说，这似乎不是一个问题。
有什么建议可以让它更顺畅吗？使用UILabel修复了它，但现实生活中的归属字符串中必须有可用的链接，因此我认为无法避免UITextView。
我使用自定义UITableViewCell子类，我也简化了这些子类，但由于程序化自动布局，它们仍然是一个非常简单的读取：
class AbstractRegularTimelineCell: UITableViewCell {
weak var iconView : UIImageView!
weak var headerLabel : UILabel!
weak var timeLabel : UILabel!
weak var regularContentContainer : UIView!
weak var contentHeightConstraint : NSLayoutConstraint!
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
commonInit()
}
override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
super.init(style: style, reuseIdentifier: reuseIdentifier)
commonInit()
}
private func commonInit() {
self.selectionStyle = .None
// add the UI elements needed for all regular cells.
let iv = UIImageView(/*image: UIImage(named: "icon")*/)
iv.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(iv)
self.iconView = iv
iv.setContentCompressionResistancePriority(1000, forAxis: .Horizontal)
iv.setContentCompressionResistancePriority(1000, forAxis: .Vertical)
let hl = UILabel()
hl.numberOfLines = 0
hl.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(hl)
self.headerLabel = hl
hl.font = UIFont(name: "OpenSans-Semibold", size: UIFont.systemFontSize())
let tiv = UIImageView(/*image: UIImage(named: "timestamp")*/)
tiv.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(tiv)
let tl = UILabel()
tl.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(tl)
self.timeLabel = tl
tl.textColor = UIColor.lightGrayColor()
tl.font = UIFont(name: "OpenSans", size: UIFont.systemFontSize()-3)
let rcc = UIView()
rcc.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(rcc)
self.regularContentContainer = rcc
rcc.setContentCompressionResistancePriority(1000, forAxis: .Vertical)
rcc.setContentCompressionResistancePriority(100, forAxis: .Horizontal)
self.contentView.sendSubviewToBack(rcc) // this might help, according to Apple Dev Forums
// now, stitch the constraints together.
let views = ["iv":iv, "hl":hl, "tl":tl, "rcc":rcc, "tiv":tiv]
self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-(15)-[iv]-(15)-[hl]-(>=15)-|", options: NSLayoutFormatOptions.DirectionLeadingToTrailing, metrics: [:], views: views))
self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-(15)-[iv]", options: NSLayoutFormatOptions.DirectionLeadingToTrailing, metrics: nil, views: views))
self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-(17)-[hl]-(8)-[rcc]", options: NSLayoutFormatOptions.DirectionLeadingToTrailing, metrics: nil, views: views))
var otherConstraints = [NSLayoutConstraint]()
var c = NSLayoutConstraint(item: tiv, attribute: .Top, relatedBy: .Equal, toItem: rcc, attribute: .Bottom, multiplier: 1, constant: 8)
c.priority = 600
otherConstraints.append(c)
c = NSLayoutConstraint(item: tiv, attribute: .Top, relatedBy: .GreaterThanOrEqual, toItem: rcc, attribute: .Bottom, multiplier: 1, constant: 6)
otherConstraints.append(c)
c = NSLayoutConstraint(item: tl, attribute: .Leading, relatedBy: .Equal, toItem: tiv, attribute: .Trailing, multiplier: 1, constant: 6)
otherConstraints.append(c)
c = NSLayoutConstraint(item: tiv, attribute: .CenterY, relatedBy: .Equal, toItem: tl, attribute: .CenterY, multiplier: 1, constant: 1)
otherConstraints.append(c)
c = NSLayoutConstraint(item: self.contentView, attribute: .Bottom, relatedBy: .Equal, toItem: tiv, attribute: .Bottom, multiplier: 1, constant: 10)
otherConstraints.append(c)
c = NSLayoutConstraint(item: tiv, attribute: .Leading, relatedBy: .Equal, toItem: hl, attribute: .Leading, multiplier: 1, constant: 0)
otherConstraints.append(c)
c = NSLayoutConstraint(item: rcc, attribute: NSLayoutAttribute.Height, relatedBy: .LessThanOrEqual, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 10000)
otherConstraints.append(c)
self.contentHeightConstraint = c
c = NSLayoutConstraint(item: self.contentView, attribute: .Trailing, relatedBy: .GreaterThanOrEqual, toItem: rcc, attribute: .Trailing, multiplier: 1, constant: 15)
otherConstraints.append(c)
c = NSLayoutConstraint(item: rcc, attribute: .Leading, relatedBy: .Equal, toItem: hl, attribute: .Leading, multiplier: 1, constant: 0)
otherConstraints.append(c)
self.contentView.addConstraints(otherConstraints)
}
}
class ExampleCell: AbstractRegularTimelineCell {
weak var textView : UITextView!
override required init(style: UITableViewCellStyle, reuseIdentifier: String?) {
super.init(style: style, reuseIdentifier: reuseIdentifier)
self.setupTextView()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
self.setupTextView()
}
private func setupTextView() {
let t = UITextView()
t.translatesAutoresizingMaskIntoConstraints = false
self.regularContentContainer.addSubview(t)
self.regularContentContainer.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|[t]|", options: NSLayoutFormatOptions.DirectionLeadingToTrailing, metrics: [:], views: ["t":t]))
self.regularContentContainer.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|[t]|", options: NSLayoutFormatOptions.DirectionLeadingToTrailing, metrics: [:], views: ["t":t]))
self.textView = t
t.scrollEnabled = false
}
}
较少冗长的View Controller代码：
class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
weak var tableView : UITableView!
override func viewDidLoad() {
super.viewDidLoad()
let t = UITableView()
t.registerClass(ExampleCell.classForCoder(), forCellReuseIdentifier: "example")
t.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(t)
self.tableView = t
self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|[t]|", options: NSLayoutFormatOptions.DirectionLeadingToTrailing, metrics: [:], views: ["t":t]))
self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|[t]|", options: NSLayoutFormatOptions.DirectionLeadingToTrailing, metrics: [:], views: ["t":t]))
t.delegate = self
t.dataSource = self
t.estimatedRowHeight = 350
}
func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return 1
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 300
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell : ExampleCell = tableView.dequeueReusableCellWithIdentifier("example", forIndexPath: indexPath) as! ExampleCell
cell.timeLabel.text = "probably never"
switch indexPath.row % 3 {
case 0:
cell.headerLabel.text = "First paragraph (Part one of two)"
cell.textView.text = "As any dedicated reader can clearly see, the Ideal of practical reason is a representation of, as far as I know, the things in themselves; as I have shown elsewhere, the phenomena should only be used as a canon for our understanding. These paralogisms of practical reason are what first give rise to the architectonic of practical reason."
case 1:
cell.headerLabel.text = "First paragraph, 2/2"
cell.textView.text = "As will easily be shown in the next section, reason would thereby be made to contradict, in view of these considerations, the Ideal of practical reason, yet the manifold depends on the phenomena. Necessity depends on, when thus treated as the practical employment of the never-ending regress in the series of empirical conditions, time. Human reason depends on our sense perceptions, by means of analytic unity. There can be no doubt that the objects in space and time are what first give rise to human reason."
default:
cell.headerLabel.text = "Second paragraph"
cell.textView.text = "Let us suppose that the noumena have nothing to do with necessity, since knowledge of the Categories is a posteriori. Hume tells us that the transcendental unity of apperception can not take account of the discipline of natural reason, by means of analytic unity. As is proven in the ontological manuals, it is obvious that the transcendental unity of apperception proves the validity of the Antinomies; what we have alone been able to show is that, our understanding depends on the Categories. It remains a mystery why the Ideal stands in need of reason. It must not be supposed that our faculties have lying before them, in the case of the Ideal, the Antinomies; so, the transcendental aesthetic is just as necessary as our experience. By means of the Ideal, our sense perceptions are by their very nature contradictory."
}
return cell
}
}
答案 0 :(得分：0)
正如@ A-Live在评论中指出的那样，问题在于嵌套的滚动视图。
为了使这个问题对任何人都有用，我最终用TTTAttributedLabel替换了UITextView s，这显着提高了性能。
此外，无法理解为什么iOS 9更新时性能下降的原因显着;我怀疑对autolayout引擎进行了无证的更改;如果有一个很好的解决方法，就没有必要进一步调查。