一、UISearchBar的创建

let searchBar = UISearchBar(frame: CGRect(x: 0, y: 100, width: 414, height: 50))
searchBar.showsCancelButton = true  // 取消按钮是否显示
searchBar.delegate = self
self.view.addSubview(searchBar)

注：1. Controller 要实现 UISearchBarDelegate
2. UISearchBar 的直属父类是 UIView

二、UISearchBar回调

1. 点击 cancle

func searchBarCancelButtonClicked(_ searchBar: UISearchBar) {
        print("cancel")
}

2. 点击 搜索

func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
        print("搜索")
}