How to add a subView to all UITable Cells - swift

Question

Without using storyboard.
I'm trying to add an error label to any cell where a value is not filled out/saved. I concluded that I dont need to show this logic and the issue is showing more than one error labels in all/more than one tableView's cell.
I've created this viewLabel to reuse:
struct Label {
static let errorLabel: UILabel = {
let label = UILabel()
label.frame = CGRect(x: 0, y: 0, width: 18, height: 18)
label.text = "!"
label.layer.cornerRadius = label.frame.height / 2
label.backgroundColor = UIColor.red
label.translatesAutoresizingMaskIntoConstraints = false
label.textAlignment = .center
label.textColor = UIColor.white
label.font = UIFont(name: "CircularStd-Black", size: 14)
label.clipsToBounds = true
return label
}()
}
Inside cellForRowAt:
// I'm using detailTextLabel
let cell = UITableViewCell(style: .value1, reuseIdentifier: cellId)
cell.addSubview(Label.errorLabel)
// [...] constraints for Label.errorLabel
return cell
Based on this example, I'd expect to show a red circle on all cells but instead, it shows on the last cell. Why?

Answer 1

A few things wrong here:
You should only add to cell contentView. (https://developer.apple.com/documentation/uikit/uitableviewcell/1623229-contentview)
Example:
cell.contentView.addSubview(myLabel)
Better reuse would be to add your, label once.
This can be done in interface builder or init or awakeFromNib. This way reuse will be more efficient.
And this is the main issue you are seeing:
You are adding one static label, again and again.
Meaning: only the last cell will display it because there is only one label (:
Better use a function to create the label (Factory function)
static func createLabel() -> UILabel {
let label = UILabel()
label.frame = CGRect(x: 0, y: 0, width: 18, height: 18)
label.text = "!"
label.layer.cornerRadius = label.frame.height / 2
label.backgroundColor = UIColor.red
label.translatesAutoresizingMaskIntoConstraints = false
label.textAlignment = .center
label.textColor = UIColor.white
label.font = UIFont(name: "CircularStd-Black", size: 14)
label.clipsToBounds = true
return label
}