自从升级到iOS 9之后,以前运行良好的代码开始在滚动方面表现出非常糟糕的性能。
我试图从头开始创建一个最小的示例,省去了单元的大部分配置以及各种缓存和内容生成代码。然而,代码仍然不是一个快速阅读的过程,而且分析结果也有所不同:/
根据苹果开发者论坛(
编辑
:我找到了
link
)这可能是因为自动布局发生了变化,并且在其superView的后面使用了布局繁重的视图,使其不那么糟糕,仍然不足以发布。
我怀疑问题出在
UIKit
,尤其是在自动布局和
UITextView
当我开始设置时,滚动条立刻变粗了
cell.textView.text
.
有人做过类似的观察吗?对于许多人来说,这似乎不是一个问题。
有什么建议可以让这更顺利吗?使用
UILabel
s修复了它,但在现实生活中,属性字符串中有一些链接是可以录制的,所以我认为没有办法避免
UI文本视图
.
我正在使用自定义
UITableViewCell
子类,我也简化了,但由于程序化的自动布局,它们仍然很容易阅读:
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
}
}
不太长的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
}
}
