UITableView performance problem with HeaderCell - swift

Question

I have a performance issue when HeaderCell becomes visible, it takes up to 40% of CPU on iPhone X and I see lags. This UITableView displays static data (TV guide). I see lags every time when I scroll up and down, "tableView.dequeueReusableCell()" doesn't help. If I use my ExpandableHeaderView() to create HeaderCell for supporting tapping and expanding section, I have the same issue. If expand section and scrolls inside elements, I do not see lags. Performance problem occurs only when HeaderCell appears on the screen. When user opens View Controller, he sees 3 programs for each channel (current and next two), if he taps on section name, he sees all programs for section (channel). HeaderCell contains only Label. I display the same data in the same way on my Android app and it works without any problems on simple Android device.
func numberOfSections(in tableView: UITableView) -> Int {
return Channels.count
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return Channels[section].Programs.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier)! as! TVGuideTableViewCell
let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "HH:mm"
let text = Channels[indexPath.section].Programs[indexPath.row].Name
let dateString = dateFormatter.string(from:Channels[indexPath.section].Programs[indexPath.row].StartDate!)
cell.label.text = text
cell.timeLabel.text = dateString
if (Channels[indexPath.section].Programs[indexPath.row].EndDate! < currentDate) {
cell.label.textColor = UIColor.gray
} else {
cell.label.textColor = UIColor.white
}
if (Channels[indexPath.section].Programs[indexPath.row].StartDate! < currentDate) {
cell.bell.isHidden = true
} else {
cell.bell.isHidden = false
}
if (Channels[indexPath.section].Programs[indexPath.row].EndDate! < currentDate) {
Channels[indexPath.section].Programs[indexPath.row].expandedRow = false
} else {
if Channels[indexPath.section].expandedCount < 3 {
Channels[indexPath.section].expandedCount += 1
Channels[indexPath.section].Programs[indexPath.row].expandedRow = true
}
}
return cell
}
func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
let headerCell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifierHeader) as! CustomHeaderTableViewCell
headerCell.headerLabel.text = Channels[section].Name
return headerCell
// let header = ExpandableHeaderView()
// header.customInit(title: Channels[section].Name, section: section, delegate: self as ExpandableHeaderViewDelegate)
// return header
}
func toggleSection(header: ExpandableHeaderView, section: Int) {
Channels[section].expanded = !Channels[section].expanded
Channels[section].expandedCount = 0
tableView.beginUpdates()
for i in 0 ..< Channels[section].Programs.count {
tableView.reloadRows(at: [IndexPath(row: i, section: section)], with: .automatic)
}
tableView.endUpdates()
}
func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
return 38
}
func tableView(_ tableView: UITableView, heightForFooterInSection section: Int) -> CGFloat {
return 2
}
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
if(Channels[indexPath.section].expanded) {
return 38
} else {
if (Channels[indexPath.section].Programs[indexPath.row].EndDate! < currentDate) {
return 0
} else {
if Channels[indexPath.section].Programs[indexPath.row].expandedRow {
return 38.0
} else {
return 0.0
}
}
}
}
class CustomHeaderTableViewCell: UITableViewCell {
#IBOutlet weak var headerLabel: UILabel!
override func awakeFromNib() {
super.awakeFromNib()
// Initialization code
}
override func setSelected(_ selected: Bool, animated: Bool) {
super.setSelected(selected, animated: animated)
// Configure the view for the selected state
}
}

Answer 1

From your code, what I can see that the problem is not HeaderCell, the problem is DateFormatter object. Because everytime you scroll and cell appears a new object is created and just imagine that if there are 10 - 15 cells at a time then 10 - 15 reused / created and as you scroll or reloadData it again create a new object.
So, my advise is to create the DateFormatter object outside cellforRow and then just use it to get to get a dateString by calling it.
This is just one assumption, try this and project still appears do let me know!