How to disable caching from NSURLSessionTask

Question

In my iOS app, I am using NSURLSessionTask to download json data to my app. I discovered that when I call the url directly from the browser, I get an up to date json and when it's called from within the app, I get an older version of the json.

Is this due to caching? How can I tell NSURLSessionTask to not use caching.

This is the call I use:

NSURLSessionTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {

Thanks!

Answer 1

If your read the links from @runmad you can see in the flow chart that if the HEAD of the file is unchanged it will still used the cached version when you set the cachePolicy.

In Swift3 I had to do this to get it to work:

let config = URLSessionConfiguration.default
config.requestCachePolicy = .reloadIgnoringLocalCacheData
config.urlCache = nil

let session = URLSession(configuration: config)

That got a truly non-cached version of the file, which I needed for bandwidth estimation calculations.

Answer 2

Swift 3, Xcode 8

extension UIImageView {
func donloadImage(fromUrl url: URL) {
    let request = URLRequest(url: url, cachePolicy: URLRequest.CachePolicy.reloadIgnoringLocalCacheData, timeoutInterval: 60.0)
    URLSession.shared.dataTask(with: request) { (data, response, error) in
        guard
            let httpURLResponse = response as? HTTPURLResponse, httpURLResponse.statusCode == 200,
            let mimeType = response?.mimeType, mimeType.hasPrefix("image"),
            let data = data, error == nil,
            let image = UIImage(data: data)
            else { return }
        DispatchQueue.main.async() { () -> Void in
            self.image = image
        }
    }.resume()
}

Answer 3

You need to set the cachePolicy on NSURLRequest, here's the documentation.

Here's some insight as to how caching works in general.

You can read about the specific enums you can use for specifying the cachePolicy here in particular:

enum
{
   NSURLRequestUseProtocolCachePolicy = 0,
   NSURLRequestReloadIgnoringLocalCacheData = 1,
   NSURLRequestReturnCacheDataElseLoad = 2,
   NSURLRequestReturnCacheDataDontLoad = 3,
};
typedef NSUInteger NSURLRequestCachePolicy;

For example, you would do:

NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:60.0];

Answer 4

Rather than using the sharedSession, you also can create your own NSURLSession using a NSURLSessionConfiguration that specifies a default cache policy. So, define a property for your session:

@property (nonatomic, strong) NSURLSession *session;

And then:

NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
configuration.requestCachePolicy = NSURLRequestReloadIgnoringLocalCacheData;
self.session = [NSURLSession sessionWithConfiguration:configuration];

Then requests using that session will use that requestCachePolicy.

Answer 5

I was getting cache image for same url .. so i have done this

imageView.imageFromUrl(self.shareData.userResponseData["photo"] as! String)

extension UIImageView {

public func imageFromUrl(urlString: String) {

    if let url = NSURL(string: urlString) {

        let request = NSURLRequest(URL: url, cachePolicy: NSURLRequestCachePolicy.ReloadIgnoringLocalCacheData, timeoutInterval: 60.0)

        NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) {

            (response: NSURLResponse!, data: NSData!, error: NSError!) -> Void in
            self.image = UIImage(data: data)

        }
    }
}

}

Answer 6

Swift 4 & 5

I know it's been a while, but in case it might help someone in the future.

You may also use .ephemeral configuration property of URLSession, which doesn't save any cookies and caches by default.

As documentation goes,

An ephemeral session configuration object is similar to a default session configuration, except that the corresponding session object doesn’t store caches, credential stores, or any session-related data to disk. Instead, session-related data is stored in RAM.

So, your code might look like this:

let configuration = URLSessionConfiguration.ephemeral
let session = URLSession(configuration: configuration)

Answer 7

Used http method POST, like:

  var request = URLRequest(url: ulr)
  request.httpMethod = "POST"

Answer 8

The below code worked for me, the catch is setting URLCache to nil.

 NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
    config.requestCachePolicy = NSURLRequestReloadIgnoringLocalCacheData;
    config.URLCache = nil;