问题描述
在collectionCell的conentView中,我想根据不同的值限制具有不同高度的垂直子视图,但是问题是,当内容从屏幕上滚动出然后在屏幕上向后滚动时,高度会意外地改变:>
向下滚动屏幕,然后向后滚动(由于未知原因,视图的高度已更改):
下面是布局代码:
let contentView = cell.contentView
let row = indexPath.row
//calculate view height: relativeHeight value
let cellHeight = cell.frame.height
var relativeHeight = 0.6 * cellHeight
let values = [112.0,116.0,86.0,95.0,67.0,76.0,34.0,43.0,24.0,35.0,47.0,66.0,57.0,36.0,64.0,23.0,22.0,20.0,23.0]
let Δvalue = values.max()! - values.min()!
let value = values[row]
if Δvalue != 0 {
let different = value - values.min()!
let ratio = CGFloat(different / Δvalue)
relativeHeight = ratio * relativeHeight
}
if contentView.subviews.count == 0 {
//time label
let timeLabel = UILabel()
timeLabel.tag = 3
timeLabel.textColor = self.textColor
timeLabel.font = UIFont.boldSystemFont(ofSize: 13)
contentView.addSubview(timeLabel)
timeLabel.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
timeLabel.bottomAnchor.constraint(equalTo: contentView.bottomAnchor,constant: -4),timeLabel.leadingAnchor.constraint(equalTo: contentView.leadingAnchor)
])
//vertical view
let valueView = UIView()
valueView.tag = 1
valueView.backgroundColor = UIColor.systemBlue.withAlphaComponent(0.382) //1-0.618
contentView.addSubview(valueView)
valueView.translatesAutoresizingMaskIntoConstraints = false
//valueView.constraints.forEach{ $0.isActive = false }
NSLayoutConstraint.activate([
valueView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor),valueView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor),valueView.bottomAnchor.constraint(equalTo: timeLabel.topAnchor,valueView.heightAnchor.constraint(equalToConstant: relativeHeight)
])
//value label
let valueLabel = UILabel()
valueLabel.tag = 2
valueLabel.textColor = self.textColor
valueLabel.font = UIFont.systemFont(ofSize: 12)
contentView.addSubview(valueLabel)
valueLabel.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
valueLabel.bottomAnchor.constraint(equalTo: valueView.topAnchor,valueLabel.centerXAnchor.constraint(equalTo: valueView.centerXAnchor)
])
}
如何解决此类布局约束问题?
非常感谢!
解决方法
我猜这是因为分配后没有参考valueView
或您要设置的heightConstraint
,请检查contentView.subviews.count == 0
。您为UICollectionViewCell
准备视图层次结构的方式可能根本不是一个好习惯。在使可重用视图出队时,必须满足所有条件才能设置动态值。如果contentView.subviews.count == 0
失败,则这里没有任何处理程序。
使用子类UICollectionViewCell
来修复CollectionViewCell: UICollectionViewCell
中所有与视图相关的任务,从而完成了修复。我添加了一个属性valueViewHeightConst
,其初始约束值为0.0。我要在计算要设置的高度值后设置确切的值。
还引入了一种缓存机制,您无需在每次使单元出队时都计算relativeHeight
。
请检查位于https://github.com/sauvikapple/StackoverflowAnsToQ63743769的最终项目。