在PDFView SWIFT中打开存储在本地存储器中的PDF

Question

我已将pdf文件下载到我的缓存中。现在，我希望在PDFView中打开此PDF文件。我已经在我的ViewController中添加了PDFView，这是相同的代码。

let pdfView = PDFView()
override func viewDidLoad() {
   super.viewDidLoad()
   view.addSubview(pdfView)
}

下面给出的代码将作为URL返回将PDF下载到的位置。

guard let pdfURL = downloader.downloadData(urlString: "https://www.tutorialspoint.com/swift/swift_tutorial.pdf", downloadType: DownloadType.cache.rawValue) else { return }

我已经检查了返回的URL，并且该文件存在。现在，在下面的代码中，我试图在pdf视图中打开它。

if let document = PDFDocument(url: pdfURL) {
   pdfView.document = document
}

下面给出的代码显示了下载数据方法。

public func downloadData(urlString : String,downloadType : String)->URL?{

        let documentsUrl:URL =  FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first as URL!
        var destinationFileUrl = documentsUrl.appendingPathComponent("downloadedFile.pdf")
        try? FileManager.default.removeItem(at: destinationFileUrl)
        guard let url = URL(string: urlString)else{
            return nil
        }
        let urlSession = URLSession(configuration: .default)
        let downloadTask = urlSession.downloadTask(with: url) { (tempLocalUrl, response, error) in
            if let tempLocalUrl = tempLocalUrl, error == nil {

                if let statusCode = (response as? HTTPURLResponse)?.statusCode {
                    print("Successfully downloaded. Status code: \(statusCode)")

                }
                if downloadType == "cache" {
                    do {
                        try? FileManager.default.removeItem(at: destinationFileUrl)
                          try FileManager.default.copyItem(at: tempLocalUrl, to: destinationFileUrl)
                    } catch (let writeError) {
                        print("Error creating a file \(destinationFileUrl) : \(writeError)")
                    }
                }
            } else {
                print("Error took place while downloading a file. Error description: %@", error?.localizedDescription);
            }
        }
        downloadTask.resume()

        return destinationFileUrl
    }

但是如果未执行let块，似乎返回了nil和其中的代码。请帮助！

Answer 1

当然没有。return destinationFileUrl，用它来初始化PDF，获取零。

它返回，而任务仍在执行中，因此路径中的文件不存在。

因为下载是异步操作。

这是completionHandler的闭包。

通常，将其转到

public func downloadData(urlString : String,downloadType : String)->URL?{

        let documentsUrl:URL =  FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first as URL!
        var destinationFileUrl = documentsUrl.appendingPathComponent("downloadedFile.pdf")
        try? FileManager.default.removeItem(at: destinationFileUrl)
        guard let url = URL(string: urlString)else{
            return nil
        }
        let urlSession = URLSession(configuration: .default)
        let downloadTask = urlSession.downloadTask(with: url) { (tempLocalUrl, response, error) in
            if let tempLocalUrl = tempLocalUrl, error == nil {

                if let statusCode = (response as? HTTPURLResponse)?.statusCode {
                    print("Successfully downloaded. Status code: \(statusCode)")

                }
                if downloadType == "cache" {
                    do {
                        try? FileManager.default.removeItem(at: destinationFileUrl)
                          try FileManager.default.copyItem(at: tempLocalUrl, to: destinationFileUrl)
                    } catch (let writeError) {
                        print("Error creating a file \(destinationFileUrl) : \(writeError)")
                    }
                }
            } else {
                print("Error took place while downloading a file. Error description: %@", error?.localizedDescription);
            }
        }
        downloadTask.resume()


        return destinationFileUrl
    }

进入

public func downloadData(urlString : String,downloadType : String, completionHandler: @escaping (URL) -> Void){

            let documentsUrl:URL =  FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first as URL!
            var destinationFileUrl = documentsUrl.appendingPathComponent("downloadedFile.pdf")
            try? FileManager.default.removeItem(at: destinationFileUrl)
            guard let url = URL(string: urlString)else{
                return nil
            }
            let urlSession = URLSession(configuration: .default)
            let downloadTask = urlSession.downloadTask(with: url) { (tempLocalUrl, response, error) in
                if let tempLocalUrl = tempLocalUrl, error == nil {

                    if let statusCode = (response as? HTTPURLResponse)?.statusCode {
                        print("Successfully downloaded. Status code: \(statusCode)")

                    }
                    if downloadType == "cache" {
                        do {
                            try? FileManager.default.removeItem(at: destinationFileUrl)
                              try FileManager.default.copyItem(at: tempLocalUrl, to: destinationFileUrl)
                                completionHandler(destinationFileUrl)
                        } catch (let writeError) {
                            print("Error creating a file \(destinationFileUrl) : \(writeError)")
                        }
                    }
                } else {
                    print("Error took place while downloading a file. Error description: %@", error?.localizedDescription);
                }
            }
            downloadTask.resume()

        }

在completionHandler回调中，初始化PDF