UIDocumentPickerViewController -代理方法未被调用

Question

我使用UIDocumentPickerViewController从文件中选择文档并将其上传到服务器。我能够成功地访问文件，但是单击文件时委托方法不会被调用。

我使用了以下代码来调用文档选择器：

class Uploads: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func uploadDocument(_ sender: Any) {

        let documentPicker = UIDocumentPickerViewController(documentTypes: [String(kUTTypePDF), String(kUTTypePlainText)], in: .import)
        documentPicker.delegate = self
        if #available(iOS 11.0, *) {
            documentPicker.allowsMultipleSelection = false
        } else {
        }
        present(documentPicker, animated: true, completion: nil)
    }

    /*
    // MARK: - Navigation

    // In a storyboard-based application, you will often want to do a little preparation before navigation
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        // Get the new view controller using segue.destinationViewController.
        // Pass the selected object to the new view controller.
    }
    */

}

extension Uploads: UIDocumentPickerDelegate {

    func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {

        print(urls.first)
    }

    func documentPickerWasCancelled(_ controller: UIDocumentPickerViewController) {
        print("Cancelled")
    }
}

我注意到在调用委托方法时会收到以下警告：

实例方法'documentPicker(:didPickDocumentsAt:)‘几乎匹配协议'UIDocumentPickerDelegate’的可选要求‘documentPicker(：UIDocumentPickerDelegate：)’ 使'documentPicker(_:didPickDocumentsAt:)‘私有以沉默此警告

我相信委托方法不会因为这个警告而被调用，虽然我不知道为什么要得到这个警告。

Answer 1

希望共享代码示例将有助于：

class ViewController : UIViewController,UIDocumentPickerDelegate{

  var documentBrowser: UIDocumentPickerViewController = {
  let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
  let browser = UIDocumentPickerViewController(documentTypes: [documentsPath], in: .open)
      browser.allowsMultipleSelection = true
      return browser
    }()

override func viewDidLoad() {
        super.viewDidLoad()
        self.addChild(documentBrowser)
        documentBrowser.view.frame = self.view.bounds
        view.addSubview(documentBrowser.view)
 }

  func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]){
       print(urls)
   }
}

Answer 2

如果采用'UIDocumentPickerDelegate‘协议的类被声明为'open’，则会出现问题。

例如，这个类将有一个问题：

open class FilePickerHelper: UIDocumentPickerDelegate

虽然这个类将，而不是，但它有一个问题：

class FilePickerHelper: UIDocumentPickerDelegate