UIDocumentBrowser在iPads上不工作，而在模拟器上工作正常[iOS，Swift]

Question

我正在学习如何在iOS中构建document-based应用程序。

我遵循了苹果的官方示例(https://developer.apple.com/documentation/uikit/view_controllers/building_a_document_browser-based_app#overview)，并尝试将其修改为显示PDF查看器。

我修改了原始示例代码以创建以下代码。它在我的Macbook Pro (2020)上的任何模拟器上都工作得很好。然而，当我测试iPads (例如，iPad迷你和PDF :新一代)时，我无法打开iPad文件。

我发现以下代码不起作用：let doc = PDFDocument(url: documentURL)。URL似乎得到了适当的获取。在使用iPads进行测试时，doc保持为nil，而在使用模拟器进行测试时，则会适当地获取。

如果你能让我知道我的代码出了什么问题，我将不胜感激。

DocumentBrowserController.swift

import UIKit
import os.log
import PDFKit

/// - Tag: DocumentBrowserViewController
class DocumentBrowserViewController: UIDocumentBrowserViewController, UIDocumentBrowserViewControllerDelegate {
    
    /// - Tag: viewDidLoad
    override func viewDidLoad() {
        super.viewDidLoad()
        delegate = self
        
        allowsDocumentCreation = true
        allowsPickingMultipleItems = false
    }
    
     //MARK: - UIDocumentBrowserViewControllerDelegate
    
    // UIDocumentBrowserViewController is telling us to open a selected a document.
    func documentBrowser(_ controller: UIDocumentBrowserViewController, didPickDocumentsAt documentURLs: [URL]) {
        if let url = documentURLs.first {
            presentDocument(at: url)
        }
    }
    
    // MARK: - Document Presentation
   var transitionController: UIDocumentBrowserTransitionController?
    
    func presentDocument(at documentURL: URL) {
        let storyBoard = UIStoryboard(name: "Main", bundle: nil)

        // Load the document's view controller from the storyboard.
        let instantiatedNavController = storyBoard.instantiateViewController(withIdentifier: "DocNavController")
        guard let docNavController = instantiatedNavController as? UINavigationController else { fatalError() }
        guard let documentViewController = docNavController.topViewController as? TextDocumentViewController else { fatalError() }
        
//        // Load the document view.
//        documentViewController.loadViewIfNeeded()
//
        // In order to get a proper animation when opening and closing documents, the DocumentViewController needs a custom view controller
        // transition. The `UIDocumentBrowserViewController` provides a `transitionController`, which takes care of the zoom animation. Therefore, the
        // `UIDocumentBrowserViewController` is registered as the `transitioningDelegate` of the `DocumentViewController`. Next, obtain the
        // transitionController, and store it for later (see `animationController(forPresented:presenting:source:)` and
        // `animationController(forDismissed:)`).
        docNavController.transitioningDelegate = self
        
        // Get the transition controller.
        transitionController = transitionController(forDocumentAt: documentURL)
        
        let doc = PDFDocument(url: documentURL)

        transitionController!.targetView = documentViewController.pdfView
  
        
        // Present this document (and it's navigation controller) as full screen.
        docNavController.modalPresentationStyle = .fullScreen

        // Set and open the document.
        documentViewController.document = doc
        os_log("==> Document Opened", log: .default, type: .debug)
        self.present(docNavController, animated: true, completion: nil)
    }
    
}

extension DocumentBrowserViewController: UIViewControllerTransitioningDelegate {
    
    func animationController(forPresented presented: UIViewController,
                             presenting: UIViewController,
                             source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        // Since the `UIDocumentBrowserViewController` has been set up to be the transitioning delegate of `DocumentViewController` instances (see
        // implementation of `presentDocument(at:)`), it is being asked for a transition controller.
        // Therefore, return the transition controller, that previously was obtained from the `UIDocumentBrowserViewController` when a
        // `DocumentViewController` instance was presented.
        return transitionController
    }
    
    func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        // The same zoom transition is needed when closing documents and returning to the `UIDocumentBrowserViewController`, which is why the the
        // existing transition controller is returned here as well.
        return transitionController
    }
    
}

TextDocumentViewController.swift

(我只是在这里发布这篇文章，尽管这段代码似乎不是问题所在)

/*
 See LICENSE folder for this sample’s licensing information.
 
 Abstract:
 A view controller for displaying and editing documents.
 */

import UIKit
import os.log
import PDFKit

var currentPage = 0

/// - Tag: textDocumentViewController
class TextDocumentViewController: UIViewController, PDFDocumentDelegate, PDFViewDelegate {
    
    @IBOutlet weak var pdfView: PDFView!
    @IBOutlet weak var doneButton: UIBarButtonItem!
    
    private var keyboardAppearObserver: Any?
    private var keyboardDisappearObserver: Any?
    
    var document: PDFDocument! {
        didSet {
            document.delegate = self
        }
    }
    
    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
        //        setupNotifications()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        //        setupNotifications()
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        pdfView.delegate = self
        doneButton.isEnabled = false
        
        if #available(iOS 13.0, *) {
            /** When turned on, this changes the rendering scale of the text to match the standard text scaling
             and preserves the original font point sizes when the contents of the text view are copied to the pasteboard.
             Apps that show a lot of text content, such as a text viewer or editor, should turn this on and use the standard text scaling.
             
             For more information, refer to the WWDC 2019 video on session 227 "Font Management and Text Scaling"
             https://developer.apple.com/videos/play/wwdc2019/227/
             (from around 30 minutes in, and to the end)
             */
        }
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        pdfView.document = document!
        pdfView.autoScales = true
        pdfView.displayMode  = .singlePage
        pdfView.displayDirection = .horizontal
        pdfView.displaysPageBreaks = true
        pdfView.pageBreakMargins = UIEdgeInsets(top: 10, left: 20, bottom: 10, right: 20)
        pdfView.usePageViewController(true)                   
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        
    }
    
    
    
}

*我简化了代码，试图清楚地说明问题(2020/10/27)

Answer 1

嗨，我想这可能是因为：

documentBrowser(_ controller: UIDocumentBrowserViewController, didPickDocumentsAt documentURLs: [URL]) 

访问沙箱外部的项目。

你能试着替换：

 presentDocument(at: url)

使用

let data = try? Data(contentsOf: url)
print(data)

如果输出为nil，则是因为URL无法加载。

然后将其替换为：

   let didObtainSecScope = url.startAccessingSecurityScopedResource()
   let data = try? Data(contentsOf: url)
   print(data, didObtainSecScope)
   url.stopAccessingSecurityScopedResource()

如果我的怀疑是正确的，它应该打印一个描述数据对象，后跟'true‘。你应该能够用你的contentsOf代码替换“数据( PDF : url)”。在使用URL时，必须维护安全范围，一旦使用完URL处的文档，就调用"url.stopAccessingSecurityScopedResource“。否则，您将泄漏内核资源。

确保不要过早调用"stopAccessingSecurityScopedResource()“。

编辑:在苹果文档中明确提到了这一点：https://developer.apple.com/documentation/uikit/view_controllers/providing_access_to_directories