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

• 使用保存文件的URL(路径(来访问下载的文件..所以我不必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"永久URL"。所以我重新启动应用程序，我没有再次运行 downloadTask(因为应该保存 MLModel？(，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)")
}

我收到此错误

file:///var/mobile/Containers/Data/Application/659B2FEE-4384-4BBE-97D1-B1575BF1EB3B/Library/Application 귑ీƢupport/CFNetworkDownload_v3EpLD.mlmodelc not exist

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

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

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，我运行了此代码以查找文件的 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)