带有加载指示器的 UISearchController

我实施了UISearchController我正在从 js 回调获取数据，但是当我录入searchbar放入数据需要一些时间，所以我想知道如何实现加载indicator进入表查看结果UISearchController

用 Swift 3 编写了这个扩展，看起来效果很好。

extension UISearchBar {

    private var textField: UITextField? {
        return subviews.first?.subviews.flatMap { $0 as? UITextField }.first
    }

    private var activityIndicator: UIActivityIndicatorView? {
        return textField?.leftView?.subviews.flatMap{ $0 as? UIActivityIndicatorView }.first
    }

    var isLoading: Bool {
        get {
            return activityIndicator != nil
        } set {
            if newValue {
                if activityIndicator == nil {
                    let newActivityIndicator = UIActivityIndicatorView(activityIndicatorStyle: .gray)
                    newActivityIndicator.transform = CGAffineTransform(scaleX: 0.7, y: 0.7)
                    newActivityIndicator.startAnimating()
                    newActivityIndicator.backgroundColor = UIColor.white
                    textField?.leftView?.addSubview(newActivityIndicator)
                    let leftViewSize = textField?.leftView?.frame.size ?? CGSize.zero
                    newActivityIndicator.center = CGPoint(x: leftViewSize.width/2, y: leftViewSize.height/2)
                }
            } else {
                activityIndicator?.removeFromSuperview()
            }
        }
    }
}

搜索结果控制器上的加载指示器 https://i.stack.imgur.com/N2Y4D.png