Set table view height based on cell height for x visible cells - ios

Question

I want to adjust my table view height so that it shows only x cells at a time. The cell's layout is configurable so I don't know its height beforehand.
For simplicity's sake, I've tried to set up the simplest example of a cell with two labels with fixed text stacked vertically.
MyCustomViewCell.swift
class MyCustomViewCell: UITableViewCell {
let label: UILabel
let label2: UILabel
override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
label = UILabel()
label2 = UILabel()
super.init(style: style, reuseIdentifier: reuseIdentifier)
self.contentView.addSubview(label)
self.contentView.addSubview(label2)
label.translatesAutoresizingMaskIntoConstraints = false
label.topAnchor.constraint(equalTo: self.contentView.topAnchor).isActive = true
label.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor).isActive = true
label.trailingAnchor.constraint(equalTo: self.contentView.trailingAnchor).isActive = true
label2.translatesAutoresizingMaskIntoConstraints = false
label2.topAnchor.constraint(equalTo: label.bottomAnchor).isActive = true
label2.trailingAnchor.constraint(equalTo: self.contentView.trailingAnchor).isActive = true
label2.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor).isActive = true
label2.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor).isActive = true
label.text = "string 1"
label2.text = "string 2"
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
I have managed to achieve the desired behavior by setting the height constraint (with a lower than 1000 priority) when initializing the table view and then setting the actual height on cellForRowAtIndexPath based on the cell's frame and the amount of cells I wanted to be visible (in this case, 5).
class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
let cellIdentifier = "cellIdentifier"
override func viewDidLoad() {
super.viewDidLoad()
let tableView = UITableView(frame: .zero, style: .plain)
setupTableViewConstraints(tableView: tableView)
tableView.register(MyCustomViewCell.self, forCellReuseIdentifier: cellIdentifier)
tableView.dataSource = self
tableView.delegate = self
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
func setupTableViewConstraints(tableView: UITableView) {
self.view.addSubview(tableView)
tableView.translatesAutoresizingMaskIntoConstraints = false
tableView.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 50).isActive = true
let heightConstraint = tableView.heightAnchor.constraint(equalToConstant: 300)
heightConstraint.priority = 900
heightConstraint.isActive = true
tableView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: 10).isActive = true
tableView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor, constant: -10).isActive = true
tableView.layer.borderColor = UIColor.black.cgColor
tableView.layer.borderWidth = 0.5
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 10000
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: cellIdentifier, for: indexPath as IndexPath) as! MyCustomViewCell
tableView.heightAnchor.constraint(equalToConstant: cell.frame.height*5).isActive = true
return cell
}
}
However, this approach doesn't seem right to me. All the way from setting a "dummy" height only to be adjusted later to setting the table view height every time cellForRowAtIndexPath is executed.
Can anyone point me in the direction of a more elegant solution?

Answer 1

In your example you are updating the height of your tableview every time it asks you to load a cell.
While this would work, it seems a bit overkill knowing that this method is constantly called by the tableview even before the cells are visible.
Why not wait until the tableview has finished loading and only then update the height?
You could do this in willDisplayCell instead which is trigged only when the cells are about to be displayed or perhaps with a completion closure like so:
self.tableView.reloadData()
DispatchQueue.main.async {
// This closure is only called when the data has been reloaded
// and thus will enable you to calculate the final content height
}