Instruments show "_NSContiguousstring" memory leak when scrolling UITableView - ios

Question

I have a UItableView which consist of 10 element. I opened Instruments to catch the memory leaks and when I scroll tableView, It started to give memory leaks. In Instruments I tried to find which causes the leaks but can't figure out, It says "_NScontiguousstring" for whole leaks.
I found some solutions for Objective-C which they check If cell is nil in "CellForRowAt" function. I don't think it is useful for Swift but I tried and as expected It doesn't work.
Memory Leak UITableView
My question is what can cause this kind of memory leak?
Devices I test it;
iPhone X on 11.3.1
iPhone 6 11.2.5
Controller Class;
class TableViewController: UITableViewController {
let teamModel = TeamModel(uid: "adsada", name: "First Team ", idea: "idea 1", slogan: "Slogan 1", university: "dasda", image: "info", isActive: true)
let teamModel2 = TeamModel(uid: "adsada", name: "Team 2", idea: "idea 2", slogan: "adasd", university: "dasda", image: "info", isActive: true)
let teamModel3 = TeamModel(uid: "adsada", name: "Team 3", idea: "idea 3", slogan: "adasd", university: "dasda", image: "info", isActive: true)
let teamModel4 = TeamModel(uid: "adsada", name: "Team 4", idea: "idea 4", slogan: "adasd", university: "dasda", image: "info", isActive: true)
let teamModel5 = TeamModel(uid: "adsada", name: "Team 5", idea: "idea 5", slogan: "adasd", university: "dasda", image: "info", isActive: true)
let teamModel6 = TeamModel(uid: "adsada", name: "Team 6", idea: "idea 6", slogan: "adasd", university: "dasda", image: "info", isActive: true)
let teamModel7 = TeamModel(uid: "adsada", name: "Team 7", idea: "idea 7", slogan: "adasd", university: "dasda", image: "info", isActive: true)
var data: [TeamModel] = []
override func viewDidLoad() {
super.viewDidLoad()
tableView.register(mainTableCell.self, forCellReuseIdentifier: "mainTableCell")
data = [teamModel,teamModel2,teamModel3,teamModel4,teamModel5,teamModel6,teamModel7]
}
// MARK: - Table view data source
override func numberOfSections(in tableView: UITableView) -> Int {
// #warning Incomplete implementation, return the number of sections
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// #warning Incomplete implementation, return the number of rows
return data.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "mainTableCell", for: indexPath) as! mainTableCell
let cell_data = data[indexPath.row]
cell.cell_data = cell_data
return cell
}
override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
return 120
}
}
Cell Class;
class mainTableCell: UITableViewCell{
var cell_data: TeamModel?{
didSet{
guard let unwrappedCell = cell_data else { return }
if let url = unwrappedCell.imageURL{
profileImage.image = UIImage(named: "info")
} else{
self.profileImage.image = UIImage(named: "info")
}
self.teamLbl.text = unwrappedCell.name
mainBackground.backgroundColor = UIColor.gray
}
}
let mainBackground: UIView = {
let v = UIView()
v.layer.cornerRadius = 8
v.layer.masksToBounds = true
return v
}()
var isVoteable: Bool = false
//let shadowView = ShadowView()
let profileImage: UIImageView = {
let imageView = UIImageView()
imageView.contentMode = .scaleAspectFill
imageView.clipsToBounds = true
imageView.layer.masksToBounds = true
return imageView
}()
let teamLbl: UILabel = {
let label = UILabel()
label.textColor = UIColor.black
label.numberOfLines = 1
label.adjustsFontSizeToFitWidth = true
return label
}()
let myVoteLbl: UILabel = {
let l = UILabel()
l.text = "Oyum: --"
return l
}()
let voteBtn: UIButton = {
let b = UIButton(type: .custom)
b.setImage(UIImage(named: "info"), for: .normal)
return b
}()
override init(style: UITableViewCellStyle, reuseIdentifier: String?){
super.init(style: style, reuseIdentifier: reuseIdentifier)
setupViews()
}
func setupViews() {
self.backgroundColor = UIColor.white
self.mainBackground.addSubview(profileImage)
self.mainBackground.addSubview(teamLbl)
self.mainBackground.addSubview(voteBtn)
self.mainBackground.addSubview(myVoteLbl)
//self.addSubview(shadowView)
self.addSubview(mainBackground)
self.backgroundColor = UIColor.clear
profileImage.translatesAutoresizingMaskIntoConstraints = false
teamLbl.translatesAutoresizingMaskIntoConstraints = false
voteBtn.translatesAutoresizingMaskIntoConstraints = false
myVoteLbl.translatesAutoresizingMaskIntoConstraints = false
mainBackground.translatesAutoresizingMaskIntoConstraints = false
//shadowView.translatesAutoresizingMaskIntoConstraints = false
}
override func layoutSubviews() {
super.layoutSubviews()
// self.setCircularImageView()
mainBackground.anchor(self.topAnchor, left: self.leftAnchor, bottom: self.bottomAnchor, right: self.rightAnchor, topConstant: 10, leftConstant: 10, bottomConstant: 10, rightConstant: 10, widthConstant: 0, heightConstant: 0)
// shadowView.anchor(self.topAnchor, left: self.leftAnchor, bottom: self.bottomAnchor, right: self.rightAnchor, topConstant: 5, leftConstant: 5, bottomConstant: 5, rightConstant: 5, widthConstant: 0, heightConstant: 0)
profileImage.anchor(nil, left: self.mainBackground.leftAnchor, bottom: nil, right: nil, topConstant: 0, leftConstant: 10, bottomConstant: 0, rightConstant: 0, widthConstant: 60, heightConstant: 60)
profileImage.anchorCenterYToSuperview()
teamLbl.anchor(self.mainBackground.topAnchor, left: profileImage.rightAnchor, bottom: nil, right: self.voteBtn.leftAnchor, topConstant: 20, leftConstant: 20, bottomConstant: 0, rightConstant: 0, widthConstant: 0, heightConstant: 40)
myVoteLbl.anchor(nil, left: profileImage.rightAnchor, bottom: self.mainBackground.bottomAnchor, right: nil, topConstant: 0, leftConstant: 20, bottomConstant: 20, rightConstant: 0, widthConstant: 0, heightConstant: 0)
voteBtn.anchor(nil, left: nil, bottom: nil, right: self.mainBackground.rightAnchor, topConstant: 0, leftConstant: 0, bottomConstant: 0, rightConstant: 0, widthConstant: 80, heightConstant: 80)
voteBtn.anchorCenterYToSuperview()
}
func setCircularImageView() {
self.profileImage.layer.cornerRadius = CGFloat(roundf(Float(self.profileImage.frame.size.width / 2.0)))
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
EDIT: I add prepareForReuse method regarding to below answer but now cells show just white. Am I doing something wrong?
override func prepareForReuse() {
super.prepareForReuse()
teamLbl.text = ""
myVoteLbl.text = ""
profileImage.image = nil
}
I also make cell_data variable "weak var cell_data: TeamModel? and nil it in prepareForReuse() method but still same leaks are coming.
EDIT 2: Full project;
https://github.com/emreond/TableView-Memory-Leak-Project
EDIT 3: I found that when I add If check and change attributes inside didst of cell_data, some cells views look ruined. For example when I change teamLbl text color inside cell_data. In some cells, It looks ruined.
EDIT 4: When I comment anchor codes to check with reference of #Darp's answer,(I don't have anything seen on screen and don't have any constraint) It still continue to give leak.
EDIT 5: I'm still working on this leak but can't find any solution. Actually when I look what is in memory when tableView is on screen, I see that only 8 cell is on memory which looks like correct.

Answer 1

I have the same problem with _NSContiguousString. Even in an empty application with just one label, it shows a leak of 48 bytes.
I am not sure, but I have a guess that the reason for leaking might be bridging with NSString (I see also [_SwiftNativeNSStringBase retain] on the top of the stack trace).
I've found out that NSString itself might be considered as a leaking object by the Instruments because it has been implemented as a Singleton.
My own question is here: Memory leaks when assigning text to UILabel (iOS, Swift 4, XCode9)

Answer 2

First things first.
Inside layoutSubviews you are setting anchores. Why ? It's going to be called each time your cells will be called.
Instead of this, move
// self.setCircularImageView()
mainBackground.anchor(self.topAnchor, left: self.leftAnchor, bottom: self.bottomAnchor, right: self.rightAnchor, topConstant: 10, leftConstant: 10, bottomConstant: 10, rightConstant: 10, widthConstant: 0, heightConstant: 0)
// shadowView.anchor(self.topAnchor, left: self.leftAnchor, bottom: self.bottomAnchor, right: self.rightAnchor, topConstant: 5, leftConstant: 5, bottomConstant: 5, rightConstant: 5, widthConstant: 0, heightConstant: 0)
profileImage.anchor(nil, left: self.mainBackground.leftAnchor, bottom: nil, right: nil, topConstant: 0, leftConstant: 10, bottomConstant: 0, rightConstant: 0, widthConstant: 60, heightConstant: 60)
profileImage.anchorCenterYToSuperview()
teamLbl.anchor(self.mainBackground.topAnchor, left: profileImage.rightAnchor, bottom: nil, right: self.voteBtn.leftAnchor, topConstant: 20, leftConstant: 20, bottomConstant: 0, rightConstant: 0, widthConstant: 0, heightConstant: 40)
myVoteLbl.anchor(nil, left: profileImage.rightAnchor, bottom: self.mainBackground.bottomAnchor, right: nil, topConstant: 0, leftConstant: 20, bottomConstant: 20, rightConstant: 0, widthConstant: 0, heightConstant: 0)
voteBtn.anchor(nil, left: nil, bottom: nil, right: self.mainBackground.rightAnchor, topConstant: 0, leftConstant: 0, bottomConstant: 0, rightConstant: 0, widthConstant: 80, heightConstant: 80)
voteBtn.anchorCenterYToSuperview()
Just bellow setupViews() call.
Next thing is that you didn't implement prepareForReuse(), you need to nil the values which u are setting in cellForRow, willDislayCell` etc.
EDIT
var cell_data: TeamModel? - Marking it as optional doesn't make it weak reference, mark it as weak var and nil it every time cell gets reused.