如何在不使用常量的情况下获得分组的UITableViewCell内容区域宽度

func tableView(_ tableView: UITableView, widthForHeaderInSection section: Int) -> CGFloat {
    let screenWidth = UIScreen.main.bounds.width
    return screenWidth
}

override func viewDidLoad() {
    super.viewDidLoad()
    tableView.estimatedRowHeight = 44
    tableView.rowHeight = UITableView.automaticDimension
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
    cell.textLabel?.text = "Cell Content"
    cell.textLabel?.numberOfLines = 0
    cell.textLabel?.translatesAutoresizingMaskIntoConstraints = false
    cell.textLabel?.leadingAnchor.constraint(equalTo: cell.leadingAnchor, constant: 15).isActive = true
    cell.textLabel?.trailingAnchor.constraint(equalTo: cell.trailingAnchor, constant: -15).isActive = true
    cell.textLabel?.topAnchor.constraint(equalTo: cell.topAnchor, constant: 0).isActive = true
    cell.textLabel?.bottomAnchor.constraint(equalTo: cell.bottomAnchor, constant: 0).isActive = true
    return cell
}