URLSession.datatask with request block not called in background
URLSession
The data task block is not called when the application is in the background and it gets stuck dataTask
with a request.
When I open the application, the block is called. By the way, I'm using query https
.
This is my code:
let request = NSMutableURLRequest(url: URL(string: url as String)!,
cachePolicy: .reloadIgnoringCacheData,
timeoutInterval:20)
request.httpMethod = method as String
request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
let session = URLSession.shared
let data = params.data(using: String.Encoding.utf8.rawValue)
request.httpBody = data
session.dataTask(with: request as URLRequest,completionHandler:
{(data, response, error) -> Void in
if error == nil
{
do {
let result = try JSONSerialization.jsonObject(with: data!, options:
JSONSerialization.ReadingOptions.mutableContainers)
print(result)
completionHandler(result as AnyObject?,nil)
}
catch let JSONError as NSError{
completionHandler(nil,JSONError.localizedDescription as NSString?)
}
}
else{
completionHandler(nil,error!.localizedDescription as NSString?)
}
}).resume()
Works great when the app is active. There is something wrong in my code. please point me
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If you want the download to continue after your app is no longer in the foreground, you must use a background session. The main limitations of background sessions are described in Downloading files in the background , and in essence:
Use delegate based
URLSession
with backgroundURLSessionConfiguration
.Use only load and unload tasks without completion handlers.
On iOS, inject the
application(_:handleEventsForBackgroundURLSession:completionHandler:)
app delegate while keeping the completion handler and starting a background session.Implement
urlSessionDidFinishEvents(forBackgroundURLSession:)
in yoursURLSessionDelegate
by invoking the stored completion handler so that the OS knows that you have finished processing the background request completion.
So, putting this together:
func startRequest(for urlString: String, method: String, parameters: String) {
let url = URL(string: urlString)!
var request = URLRequest(url: url, cachePolicy: .reloadIgnoringCacheData, timeoutInterval: 20)
request.httpMethod = method
request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
request.httpBody = parameters.data(using: .utf8)
BackgroundSession.shared.start(request)
}
Where
class BackgroundSession: NSObject {
static let shared = BackgroundSession()
static let identifier = "com.domain.app.bg"
private var session: URLSession!
#if !os(macOS)
var savedCompletionHandler: (() -> Void)?
#endif
private override init() {
super.init()
let configuration = URLSessionConfiguration.background(withIdentifier: BackgroundSession.identifier)
session = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
}
func start(_ request: URLRequest) {
session.downloadTask(with: request).resume()
}
}
extension BackgroundSession: URLSessionDelegate {
#if !os(macOS)
func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
DispatchQueue.main.async {
self.savedCompletionHandler?()
self.savedCompletionHandler = nil
}
}
#endif
}
extension BackgroundSession: URLSessionTaskDelegate {
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
if let error = error {
// handle failure here
print("\(error.localizedDescription)")
}
}
}
extension BackgroundSession: URLSessionDownloadDelegate {
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
do {
let data = try Data(contentsOf: location)
let json = try JSONSerialization.jsonObject(with: data)
print("\(json)")
// do something with json
} catch {
print("\(error.localizedDescription)")
}
}
}
And the iOS app delegate does:
func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) { BackgroundSession.shared.savedCompletionHandler = completionHandler }
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[URLSessionDownloadTask setDownloadTaskDidWriteDataBlock:^(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, int64_t bytesWritten, int64_t totalBytesWritten, int64_t totalBytesExpectedToWrite) {
CGFloat percentDone = (double)(totalBytesWritten)/(double)totalBytesExpectedToWrite;
[SVProgressHUD showWithStatus:[NSString stringWithFormat:@"%.2f%%",percentDone*100]];
}];
[downloadTask resume];
// Apply as shown in the picture
/ ********************* /
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@Rob thanks for your answer. How can I get mine json
instead of print("\(json)")
in startRequest
? Because I need to send to another class to handle if its an error, or if its data, convert it to my model correctly. I also tried your code from this link , but my background code stops at guard let data = data, error == nil else {
and just returns if I open it (I don't want that). PS: Sorry SO does not allow me to add a comment to your answer
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