How do I properly cache a NSURLRequest in swift? - ios

Question

Forgive if this has been asked but I've done heavy searching and can't seem to find an answer I'm looking for in swift. I have a UIWebView that loads PDF files and I wouldn't want the user to go through a tedious loading process again if they exit the WebView and come back, so how do I cache a request to make the loading quicker?
Here is my code:
var contentUrlPassedOn: String!
override func viewDidLoad() {
super.viewDidLoad()
myWebView.delegate = self
let url: NSURL! = NSURL(string: contentUrlPassedOn)
myWebView.loadRequest(NSURLRequest(URL: url))
var request: NSURLRequest
}
UPDATE
What I am trying to accomplish can be seen in this video
that is an example of dropbox's iOS app. When one of the files have been already loaded, every other trip into that file ( in this case PDF) will be quick and easy. This method is exactly what I am trying to replicate.
any suggestions?

Answer 1

GIF
The first time you enter this ViewController,you can see download progress
Then second time, it just load local file.So it is very quick
And code
class ViewController: UIViewController,NSURLSessionDownloadDelegate{
var sesson:NSURLSession!
var webview:UIWebView!
var progressView:UIProgressView!
override func viewDidLoad() {
super.viewDidLoad()
self.sesson = NSURLSession(configuration: NSURLSessionConfiguration.defaultSessionConfiguration(), delegate: self, delegateQueue: NSOperationQueue.mainQueue())
self.webview = UIWebView(frame: self.view.frame)
self.view.addSubview(webview)
let documentDir = NSFileManager.defaultManager().URLsForDirectory(NSSearchPathDirectory.DocumentDirectory, inDomains: NSSearchPathDomainMask.UserDomainMask).first as! NSURL
let pdfFilePath = documentDir.URLByAppendingPathComponent("Test.pdf");
if NSFileManager.defaultManager().fileExistsAtPath(pdfFilePath.path!){
let request = NSURLRequest(URL: pdfFilePath)
webview.loadRequest(request)
}else{
progressView = UIProgressView(progressViewStyle: UIProgressViewStyle.Default);
progressView.frame = CGRectMake(0, 0,200, 4)
progressView.progress = 0
progressView.progressTintColor = UIColor.blueColor()
progressView.center = self.view.center
self.view.addSubview(progressView)
let remoteURL = "https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/URLLoadingSystem/URLLoadingSystem.pdf"
let request = NSURLRequest(URL: NSURL(string: remoteURL)!)
let downloadTask = self.sesson.downloadTaskWithRequest(request)
downloadTask.resume()
}
// Do any additional setup after loading the view, typically from a nib.
}
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didFinishDownloadingToURL location: NSURL) {
if progressView != nil{
progressView.removeFromSuperview()
}
let documentDir = NSFileManager.defaultManager().URLsForDirectory(NSSearchPathDirectory.DocumentDirectory, inDomains: NSSearchPathDomainMask.UserDomainMask).first as! NSURL
let pdfFilePath = documentDir.URLByAppendingPathComponent("Test.pdf");
NSFileManager.defaultManager().moveItemAtURL(location, toURL: pdfFilePath, error: nil)
let request = NSURLRequest(URL: pdfFilePath)
self.webview.loadRequest(request)
}
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
var curprogress = Float(totalBytesWritten)/Float(totalBytesExpectedToWrite)
progressView.progress = curprogress
}
}

Answer 2

NSURLConnection (and NSURLSession's shared session) uses a shared cache. You can configure the policies of that cache to use on-disk storage, but my vague recollection is that iOS uses only an in-memory cache by default. Have a look at the NSURLCache class, and do the Swift equivalent of:
NSString *myPath = ... // some subdirectory in your app's caches directory
NSURLCache *cache = [[NSURLCache alloc] initWithCapacity:2048576 /* 2M */
diskCapacity: 134217728 /* 128M */
path:myPath];
[NSURLCache setSharedURLCache:cache];
or whatever, and you'll probably have better luck.
Note that the on-disk cache in iOS is still temporary, and can be deleted by the OS, but only when your app is not running (assuming that hasn't changed recently).
Something like
let cacheDirectory = NSSearchPathForDirectoriesInDomains(.CachesDirectory, .UserDomainMask, true)[0] as String
var dir = cacheDir.stringByAppendingFormat("/urlCache/")
var cache = NSURLCache(memoryCapacity: 2048576,
diskCapacity: 134217728,
path: dir)
NSURLCache.setSharedURLCache(cache)
but I'm not all that familiar with Swift, so I could be getting the syntax wrong.