wkwebview无法从documentsURL加载基本URL

Question

Webkit从.documentsURL html网页加载，iOS设备没有显示图片，js，css文件，在模拟器上运行正常。在我编写的代码中，我的错误是什么？

let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
        let documentsURL = URL(fileURLWithPath: documentsPath, isDirectory: true)

        let urltostr = documentsURL.absoluteString
        //print(urltostr)
        let htmlurl = urltostr+"0/index.html"
        let finalURL = URL(string: htmlurl)
        let base = urltostr+"0/"
        let baseUrl = URL(string: base)
        //let baseUrl = URL(fileURLWithPath: base, isDirectory: true)
        do {
            let fileName  = try String(contentsOf: finalURL!)
            webview.loadHTMLString(fileName as String, baseURL: baseUrl)
        } catch {
            // catch error
            print("Error web view get html")
        }