Swift 4：删除UISearchbar的编辑阴影

Question

我是swift的新手，我使用搜索功能

构建了一个应用程序

加载视图时，searchBar很好，但是当它开始编辑时，会出现一个阴影，我想将其删除

我在TextDidChange尝试了此代码，但它没有工作

searchBar.barTintColor = UIColor.clear
searchBar.backgroundColor = UIColor.clear
searchBar.isTranslucent = true
searchBar.setBackgroundImage(UIImage(), for: .any, barMetrics: .default)

Screenshot Before Editing ， Screenshot After Editing

代码：

func addSearchbar(){
    if #available(iOS 11.0, *) {
        let sc = UISearchController(searchResultsController: nil)
        let scb = sc.searchBar
        scb.showsCancelButton = false

        if let navigationbar = self.navigationController?.navigationBar {
            //navigationbar.tintColor = UIColor.green
            //navigationbar.backgroundColor = UIColor.yellow
            navigationbar.barTintColor = UIColor.white
        }

         navigationController?.navigationBar.tintColor = UIColor.green
         navigationItem.searchController = sc
         navigationItem.searchController?.searchBar.delegate = self
         navigationItem.searchController?.searchBar.barStyle = .blackTranslucent
         navigationItem.hidesSearchBarWhenScrolling = false
    }
}