Check if a file already exists before downloading it with Alamofire + suggestedDownloadDestination

问题

How can I check if a given file has been already downloaded before re-downloading it by using Alamofire? I'm using suggestedDownloadDestination so Alamofire will automatically choose the name of the file and save it in the choosen directory, for example the .CachesDirectory. The problem is that the value given by suggestedDownloadDestination is of type DownloadFileDestination which will return a NSURL only by calling him with the request's response, but in this way I could not ever know the file path without performing a request before.

This is the code I currently use to download a file with Alamofire:

Alamofire.download(.GET, downloadLink, destination: destination).progress {
                    bytesRead, totalBytesRead, totalBytesExpectedToRead in

                    }.response {
                        request, response, data, error in

                        guard error == nil else {
                            return
                        }

                        // This will give me the file path but we're already in a Request!
                        print("\(destination(NSURL(string: "")!, response!))")
                }

What am I missing?

回答1:

Not sure if you figured this out yet, but you can create an extension over Alamofire.DownloadRequest like:

extension Alamofire.DownloadRequest {
    open class func suggestedDownloadDestination(
        for directory: FileManager.SearchPathDirectory = .documentDirectory,
        in domain: FileManager.SearchPathDomainMask = .userDomainMask,
        with options: DownloadOptions)
        -> DownloadFileDestination
    {
        return { temporaryURL, response in
                let destination = DownloadRequest.suggestedDownloadDestination(for: directory, in: domain)(temporaryURL, response)
            return (destination.destinationURL, options)
        }
    }
}

Now you can specify in the options parameter if you want the file to be overwritten:

let destination =  DownloadRequest.suggestedDownloadDestination(for: .cachesDirectory,
                                                                in: .userDomainMask,
                                                                with: [DownloadRequest.DownloadOptions.removePreviousFile])

来源：https://stackoverflow.com/questions/37327874/check-if-a-file-already-exists-before-downloading-it-with-alamofire-suggestedd

标签

ios

swift

alamofire