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I am trying to experiment with constraints in Swift Playground, and going crazy. I have a small class CLListTableViewCell: UITableViewCell with a UILabel in it:

let nameLabel: UILabel = {
    let label = UILabel()
    label.text = "Here is a great text"
    label.translatesAutoresizingMaskIntoConstraints = false
    label.textAlignment = .left // text alignment in center
    return label
}()

I have a function to set up the layout, which I call at the end of init:

func addSubViewsAndLayout() {
    contentView.addSubview(nameLabel)

    let views = ["nameLabel": nameLabel]
    let horizontalConstraintsStringRepresentation = "H:|-[nameLabel]-|"

    let horizontalConstraints = NSLayoutConstraint.constraints(withVisualFormat: horizontalConstraintsStringRepresentation, options: .alignAllCenterY, metrics: nil, views: views)

    let verticalConstraintsStringRepresentation = "V:|-[nameLabel]-|"
    let verticalNameConstraints = NSLayoutConstraint.constraints(withVisualFormat: verticalConstraintsStringRepresentation, options: .alignAllLeading, metrics: nil, views: views)
    NSLayoutConstraint.activate(horizontalConstraints)
    NSLayoutConstraint.activate(verticalNameConstraints)
}

    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
    super.init(style: style, reuseIdentifier: reuseIdentifier)
    addSubViewsAndLayout()
}

All I get is a beautiful, white, empty cell. Anybody could point to what I am doing wrong here? Any missing constraint? There is no indication in the Playground console.

--- EDIT ---

The issue seems to be coming from the tableView in which I display the cell. Here is the code:

class TableViewController : UITableViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 2
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell") as? CLListTableViewCell ?? CLListTableViewCell(style: .default, reuseIdentifier: "cell")
        return cell
    }

    override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        return "Section \(section)"
    }
}

--- EDIT 2 ---

Here is a screenshot of the result.

harrouet
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  • Try setting label's text colour and background color to different values and verify that it is working or not. Because I have tried the same code in my playground and it is working. – hardik parmar Oct 13 '18 at 11:30
  • No, adding `label.backgroundColor = UIColor.clear` and `label.textColor = UIColor.black` to nameLabel definition does not change anything. However, the issue might come from the tableView. If i display the cell directly in the playground, it works. If in the tableview, it remains blank. – harrouet Oct 13 '18 at 11:54
  • can you provide a screenshot of your playground with the output? – hardik parmar Oct 13 '18 at 11:56
  • Added: a screenshot and the code of the TableViewController. – harrouet Oct 13 '18 at 12:07

1 Answers1

0

Thanks to Hardik Parmar (many thanks!), the issue was located in the fact that the playground was representing the UITableViewController, not the UITableViewCell.

After a bit of reading, I added the following before PlaygroundPage.current.liveView = myTableViewController : 

tableViewController.tableView.beginUpdates()
tableViewController.tableView.endUpdates()

This forces the tableView to redraw the cells. And now I can see my tableView correctly. I guess it would be nice if Playground did it by itself, but it seems to be necessary to force this behaviour. I hope it can help others!

harrouet
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