iOS/Swift: QLPreviewController shows blank page in iOS11

I've tried use QLPreviewController for file(.txt, .pdf, .docx, .xlsx, etc.) preview in my iOS project, but it is not working well in iOS 11: it shows blank page whatever use device or simulator. In iOS 10.3.1(simulator) it is working well, and everything is fine.

The below is the detail informations:

Environment:

Xcode version: 8.3.3, 9.0.1
Device: iPhone 7 Plus, Simulator
iOS version: 11.0.3(iPhone 7 Plus), 10.3.1(Simulator), 11.0.1(Simulator)
Swift version: 3.1/3.2

Code

import UIKit
import QuickLook

class QuickViewController: UIViewController {

    var url: String!
    var filePath: URL!
    var msg: Message! {
        didSet {
            url = msg.content
            // create document folder url
            let documentsURL =  FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
            // let tempDirectory = URL(fileURLWithPath: NSTemporaryDirectory())
            filePath = documentsURL.appendingPathComponent((msg.content as NSString).lastPathComponent)
        }
    }

    @IBOutlet weak var contentView: UIView!


    // MARK: - Initialisation

    override func viewDidLoad() {
        super.viewDidLoad()
    }

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

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        loafFile()
    }


    func loafFile() {
        if FileManager.default.fileExists(atPath: filePath.path) {
            quickLookFile()
        } else {
            AppManager_Inst.download(url: "\(url!)", destinationUrl: filePath, completion: { [unowned self](succeed, msg) in
                if succeed {
                    self.quickLookFile()
                } else {
                    print(msg)
                }
            })
        }
    }

    func quickLookFile() {

        print(filePath.path)

        /// Trying to read the file via FileManager to check if the filePath is correct or not
        let data = FileManager.default.contents(atPath: filePath.path)
        print(data)

        if QLPreviewController.canPreview(filePath as NSURL) {
            let QLController = QLPreviewController()
            QLController.delegate = self
            QLController.dataSource = self
            QLController.view.frame = self.contentView.frame
            self.view.addSubview(QLController.view)
        } else {
            print("file cannot to preview")
        }
    }

}


extension QuickViewController: QLPreviewControllerDataSource, QLPreviewControllerDelegate {

    // QLPreviewControllerDataSource

    func numberOfPreviewItems(in controller: QLPreviewController) -> Int {
        return 1
    }

    func previewController(_ controller: QLPreviewController, previewItemAt index: Int) -> QLPreviewItem {
        return filePath as NSURL
    }

    // QLPreviewControllerDelegate
    func previewController(_ controller: QLPreviewController, shouldOpen url: URL, for item: QLPreviewItem) -> Bool {
        return true
    }

}

I'm not sure what I missing or something wrong here, please help.

p.s.: I'll trying the code with iPhone 5c(iOS 10.3.1) later, and the result should update to here once I've done it.

You did not add the current viewController as the parent class of the QLPreviewController()

Just add QLController.didMove(toParentViewController: self) after adding it to the self.view

I think this should solve your issue.