App freezes / locks up when writing very large files - swift

Question

I'm downloading and writing ~200mb podcasts into the Documents directory with the following code:
var podcastRequest = NSURLRequest(URL: audioUrl)
NSURLConnection.sendAsynchronousRequest(podcastRequest, queue: NSOperationQueue.mainQueue(), completionHandler: {(response: NSURLResponse!, data: NSData!, error: NSError!) -> Void in
if let myPodcastDataFromUrl = NSData(contentsOfURL: audioUrl) {
if myPodcastDataFromUrl.writeToURL(destinationUrl, atomically: true) {
// add to the array to track the download
var tempDic = self.posts[theRow] as! NSMutableDictionary as NSMutableDictionary
tempDic["downloaded"] = "true"
self.posts[theRow] = tempDic
} else {
println("Error saving file")
}
}
})
The sendAsynchronousRequest call prevents the lockup from happening during the download, but the app still freezes when it starts actually writing it to the directory.
Is there a way to prevent the lockup from happening at all, or am I going to have to write smaller chunks at a time?

Answer 1

You won't be able to store 200MB in memory before trying to write it to disk, but you can use downloadTaskWithURL method, it writes the file to a temporary folder and you can move it when it finishes to the documents folder as follow.
let documentsDirectoryURL = NSFileManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first as! NSURL
NSURLSession.sharedSession().downloadTaskWithURL(audioUrl, completionHandler: {
(location, response, error) -> Void in
if let error = error {
println(error.description)
}
else {
if NSFileManager().moveItemAtURL(location, toURL: documentsDirectoryURL.URLByAppendingPathComponent(response.suggestedFilename!), error: nil) {
println("saved")
} else {
println("not saved.")
}
}
}).resume()