swift - footerView 中的中心按钮

Question

我希望我的按钮位于 footerView 的中心。我尝试了几种方法，但每次都失败了:

1.

    override func tableView(_ tableView: UITableView, viewForFooterInSection section: Int) -> UIView? {
        let footerView = UIView(frame: CGRect.zero)
        footerView.backgroundColor = UIColor(rgba: "#F9FAFB")
        let button = UIButton(frame: CGRect(x:(footerView.frame.size.width - 30) / 2, y:(footerView.frame.size.height - 30) / 2, width: 30, height: 30))            button.setImage(UIImage(named: "gen-cog"), for: .normal)
        button.addTarget(self, action: #selector(footerButtonAction), for: .touchUpInside)
        footerView.addSubview(button)
    }

1. 使用自动布局，这使我的按钮居中但打破了它的宽度和高度，我在上面设置为 30。

   let centerYCon = NSLayoutConstraint(item: button,
                      attribute: .centerY,
                                       relatedBy: .equal,
                                       toItem: footerView,
                                       attribute: .centerY,
                                       multiplier: 1.0,
                                       constant: 0.0);
   footerView.addConstraint(centerYCon)
   
   let centerXCon = NSLayoutConstraint(item: button,
                                           attribute: .centerX,
                                           relatedBy: .equal,
                                           toItem: footerView,
                                           attribute: .centerX,
                                           multiplier: 1.0,
                                           constant: 0.0);
   footerView.addConstraint(centerXCon)
   footerView.addSubview(button)
   

3.

button.center = footerView.center

Answer 1

  button.translatesAutoresizingMaskIntoConstraints = false
  footerView.addSubview(button)

现在再添加两个额外的约束。

  let widthConstraint = NSLayoutConstraint(item: button, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 30)
  let heightConstraint = NSLayoutConstraint(item: button, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 30)
  button.addConstraints([widthConstraint, heightConstraint])