在 Swift 中从 URL 下载并保存文件

Question

我正在尝试...

从服务器下载文件（MLModel）
将该文件保存到设备
重新启动应用程序
使用文件保存到的 URL（路径）来访问下载的文件。这样我就不必在每次应用程序启动时都重新下载它

let download = URLSession.shared.downloadTask(with: url) { (urlOrNil, response, error) in

    if let error = error {
                print("❌ There was an error in \(#function) \(error)")
                completion(nil)
                return
            }


// the location the mlModel is saved at
            guard let fileURL = urlOrNil else {print("❇️>>>\(#file) \(#line)"); return  }
            do {
                //compiles the model
                let compiledUrl = try MLModel.compileModel(at: fileURL)

            //turns the model into an MLModel
            let model = try MLModel(contentsOf: compiledUrl)
            print("newModel Complete ")


            // find the app support directory
            let fileManager = FileManager.default
            // Finds a place to save the MLModel
            let appSupportDirectory = try! fileManager.url(for: .applicationSupportDirectory,
                                                           in: .userDomainMask, appropriateFor: compiledUrl, create: true)

            // create a permanent URL in the app support directory
            let permanentUrl = appSupportDirectory.appendingPathComponent(compiledUrl.lastPathComponent)



            print("\(permanentUrl)")


            // if the file exists, replace it. Otherwise, copy the file to the destination.
            if fileManager.fileExists(atPath: permanentUrl.absoluteString) {
                _ = try fileManager.replaceItemAt(permanentUrl, withItemAt: compiledUrl)
            } else {
                try fileManager.copyItem(at: compiledUrl, to: permanentUrl)
            }

            let newModel = try MLModel(contentsOf: permanentUrl)
            print("", newModel)



            completion(newModel)
        }catch{
            print("❌ There was an error in \(#function) \(error) : \(error.localizedDescription)")
        }
    }.resume()

据我了解，这是将我的 MLModel 保存到 "permanentUrl"。所以我重新启动应用程序，我不再运行 downloadTask（因为 MLModel 应该被保存？），我尝试使用此代码访问我复制到永久 URL 的 MLModel

let permanentUrl = URL(string:"file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application%20Support/CFNetworkDownload_v3EpLD.mlmodelc")

    do {
        let model = try MLModel(contentsOf: permanentUrl!)

        print(model)
    }catch{
        print("❌ There was an error in \(#function) \(error) : \(error.localizedDescription)")
    }

我收到这个错误

file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application 귑ీƢupport/CFNetworkDownload_v3EpLD.mlmodelc does not exist" UserInfo={NSLocalizedDescription=file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application 귑ీƢupport/CFNetworkDownload_v3EpLD.mlmodelc does not exist} : file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application 귑ీƢupport/CFNetworkDownload_v3EpLD.mlmodelc does not exist

所以我猜 MLModel 没有保存？我在这里错过了什么？我假设我用 downloadTask 保存了 MLModel，但我只是没有以正确的方式检索它。如何访问我保存的文件？

Answer 1

这就是答案。

在 downloadTask 函数中，我打印了 compiledUrl.lastPathComponent 并保存了它。然后，当我重新运行应用程序时，我运行此代码找到文件的 URL。

// saved compiledUrl.lastPathComponent
    let filename = "CFNetworkDownload_B9QvT1.mlmodelc"


    let fileManager = FileManager.default
    let appSupportDirectory = try! fileManager.url(for: .applicationSupportDirectory, in: .userDomainMask, appropriateFor: nil, create: true)

    let permanentUrl = appSupportDirectory.appendingPathComponent(filename)

    let model = try? MLModel(contentsOf: permanentUrl)
    print(model)

在 Swift 中从 URL 下载并保存文件

Download And Save File From URL in Swift

swift

urlsession

coreml

mlmodel