UITableView Scroll performing animation high CPU Usage - ios

Question

I have a UITableView that is performing an animation on scroll, basically a sticky header, but instead it adjusts the height constraint of a UIView. I am getting really high CPU usage on scroll. Is there a better way to perform this animation?
Edit: I am not doing anything in the cellForRow at, function that would be causing this. It is definitely the scrollViewDidScroll function.
DidScroll:
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let offset = scrollView.contentOffset.y + tableViewContentInsets
if (lastPoint != nil) {
if (lastPoint! < offset) {
if (portfolioSummaryInitialHeight - offset < portfolioSummaryInitialHeight){
if (portfolioSummaryInitialHeight - offset > 0 ){
portfolioSummaryHeightConstraint.constant = portfolioSummaryInitialHeight - offset
} else {
portfolioSummaryHeightConstraint.constant = 0
}
}
} else {
if (portfolioSummaryInitialHeight - offset < portfolioSummaryInitialHeight){
if (portfolioSummaryInitialHeight - offset > 0 ){
portfolioSummaryHeightConstraint.constant = portfolioSummaryInitialHeight - offset
}
} else {
portfolioSummaryHeightConstraint.constant = portfolioSummaryInitialHeight
}
}
}
lastPoint = offset
}
Additional Variables:
var tableViewContentInsets: CGFloat = 80
var portfolioSummaryInitialHeight: CGFloat = 0 // equals portfolioSummaryInitialHeight at viewDidLoad
var lastPoint: CGFloat?

Answer 1

first of all, I'd advise you to check if you perform any other heavy operations on the main thread e.g data fetch or something similar. I've created a simple test project with a plain table view and a header. Here is the code which does the resizes header. According to the CPU report, it utilizes 8% of CPU in high peaks.
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var headerHeightConstr: NSLayoutConstraint! //header's height constraint
#IBOutlet weak var tableView: UITableView!
private var headerHeight: CGFloat = 128.0 ////header's height constraint initial value
override func viewDidLoad() {
super.viewDidLoad()
tableView.dataSource = self
tableView.delegate = self
}
}
extension ViewController: UITableViewDataSource {
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 100
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
guard let cell = tableView.dequeueReusableCell(withIdentifier: "reuseID") else {
return UITableViewCell(style: .default, reuseIdentifier: "reuseID")
}
return cell
}
}
extension ViewController: UITableViewDelegate {
func scrollViewDidScroll(_ scrollView: UIScrollView) {
if scrollView.contentOffset.y < 0 {
self.headerHeightConstr.constant += abs(scrollView.contentOffset.y)
} else if scrollView.contentOffset.y > 0 && self.headerHeightConstr.constant >= headerHeight {
self.headerHeightConstr.constant -= scrollView.contentOffset.y
if self.headerHeightConstr.constant < headerHeight {
self.headerHeightConstr.constant = headerHeight
}
}
}
}
This is kinda naive approach but it works, will try to answer your questions if needed.

Answer 2

Check your WillLayoutSubViews and DidLayoutSubViews functions. If you are doing lots of work in those functions then you need to add something like this:
var isScrolling: Bool = false
override func viewDidLayoutSubviews() {
if (isScrolling) {
return
} else {
super.viewDidLayoutSubviews()
}
}
While your tableView is scrolling set isScrolling = true in scrollViewDidEndDragging set isScrolling = false this will ensure that your class will not do excessive work while the tableView is scrolling but insure that it will do the work in other instances. Might not be the best way to do this but it certainly works.