ios - 每次向下滚动时如何在 UITableView 上居中显示加载 View ？

Question

下面是我使用的代码，它在普通屏幕上工作正常，但是当我在表格 View 上向下滚动时，加载 View 加载但停留在顶部。每次向下滚动时，如何在 UITableView 上居中显示加载 View ？

extension UIViewController {
    func loadWave(_ status: Bool) {
        var fadeView: UIView?

        if status == true {
            fadeView = UIView(frame: CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height))
            fadeView?.backgroundColor = UIColor.clear
            fadeView?.alpha = 0
            fadeView?.tag = 99

            let statusBarHeight: CGFloat = 20
            let navBarHeight: CGFloat = 44
            let image = UIImage(named: "image")
            loadingWaveView = UIImageView(image: image)
            loadingWaveView.center = view.center
            loadingWaveView.frame = CGRect(x: (UIScreen.main.bounds.width / 2) - (112 / 2), y: (UIScreen.main.bounds.height / 2) - (63 / 2) - statusBarHeight - navBarHeight, width: 112, height: 63)
            view.addSubview(fadeView!)
            fadeView?.addSubview(loadingWaveView)

            fadeView?.fadeTo(alphaValue: 1, withDuration: 0.2)
        } else {
            for subview in view.subviews {
                if subview.tag == 99 {
                    UIView.animate(withDuration: 0.2, animations: {
                        subview.alpha = 0
                    }, completion: { (finished) in
                        subview.removeFromSuperview()
                    })
                }
            }
        }
    }
}

Answer 1

您应该设置Autolayout constraints 使其保持在中间。

fadeView?.addSubview(loadingWaveView)
loadingWaveView.translatesAutoresizingMaskIntoConstraints = false
let horizontalConstraint = NSLayoutConstraint(item: loadingWaveView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0)
view.addConstraint(horizontalConstraint)
let verticalConstraint = NSLayoutConstraint(item: loadingWaveView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0)
view.addConstraint(verticalConstraint)