UIDocumentPickerViewController - 未调用委托方法

Question

我正在使用 UIDocumentPickerViewController 从文件中选择文档并将其上传到服务器。我能够成功访问文件，但是在单击文件时，不会调用委托方法。

我使用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( :didPickDocumentsAt:)”

将 'documentPicker(_:didPickDocumentsAt:)' 设为私有以消除此警告

我相信由于这个警告，委托方法没有被调用，尽管我不明白为什么我会收到这个警告。

Answer 1

如果采用“UIDocumentPickerDelegate”协议的类被声明为“open”，则会出现问题。

比如这个类就会有一个问题：

open class FilePickerHelper: UIDocumentPickerDelegate

而这个类不会有问题：

class FilePickerHelper: UIDocumentPickerDelegate