UIDocumentPickerViewController- didPickDocumentsAt 委托方法未在 iOS 11 中调用，在 iOS 14 中工作正常

如何解决UIDocumentPickerViewController- didPickDocumentsAt 委托方法未在 iOS 11 中调用，在 iOS 14 中工作正常

我正在使用 UIDocumentPickerViewController 向我的应用程序添加文档。但在 iOS 11 中，didPickDocumentsAt 没有被调用，因此无法进行选择。 而它在 iOS14 中运行良好。 我已经阅读了 stackoverflow 中的几乎所有线程，但没有找到解决方案。 当文档选择器在其中启动时，它是 iOS 11 中的错误吗？ Acc. to this link

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documentpicker 启动器方法：

 @IBAction func addDocBtn(_ sender: UIButton) {
    //MARK: doc-picker
    let docPicker = UIDocumentPickerViewController(documentTypes: ["public.text","com.apple.iwork.pages.pages","public.data"],in: .import)
    docPicker.delegate = self
    docPicker.modalPresentationStyle = .currentContext
    self.navigationController?.present(docPicker,animated: true,completion: nil)}

我的代表：

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

    print(urls.first as Any)
    guard let selectedFileUrl = urls.first else {
        return
    }
    let cico = selectedFileUrl as URL
    print(cico)
    selectedFileURL = cico
    print(cico.lastPathComponent)
    //hide doc btn
    //update name and add cross sign
    selectDocName = cico.lastPathComponent
    dispatchQueue.main.async {
        self.docdisplayStack.isHidden = false
        self.addDocumentBtn.isHidden = true
        self.selectedDocName.text = self.selectDocName
    }
    print(cico.pathExtension)
    let dir = FileManager.default.urls(for: .documentDirectory,in: .userDomainMask).first!
    let sandBoxUrl = dir.appendingPathComponent(selectedFileUrl.lastPathComponent)
    if FileManager.default.fileExists(atPath: sandBoxUrl.path){
        print("already exists")
        self.view.maketoast("Already Selected")
    }
    else{
        do{
            try FileManager.default.copyItem(at: selectedFileUrl,to: sandBoxUrl)
            print("copied")

        }
        catch{
            print(error)
            self.view.maketoast(error.localizedDescription)
        }
    }
}

 //this is called in everyversion but others behave differently
func documentPickerWasCancelled(_ controller: UIDocumentPickerViewController) {
    print("no items selected")
}}