downloadTaskWithRequest confusing behaviour (swift , IOS ) -

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i not understand following , hope :-)

i downloading file url (10 minutes downloadtime), works fine, when download completes.

but: when simulate crash or internet-interruption after minute , restart app again, behaves strange me. in case when restarting app download again same sessionid, seems 2 download tasks working in parallel. recognizue jumping progressbar 10% 0% , back. one, starts scratch , one, guess continious old transfer. (not sure). can restart again , there 1 more in queue.

can confirm behaviour , know how can: - continue interrupted download task (preferred :-) ) - or how can start scratch only.

here code downloading, works fine without interruption.

func download_file(surl: string, stolocation: string) {      println("start downloading ...");     println("surl : " + surl + " stolocation : " + stolocation);     bytesdownloaded=0;      var delegate = self;     delegate.storepath=stolocation;     delegate.progressview=progressview;     struct sessionproperties {         static let identifier : string! = "url_session_background_download"     }     var configuration = nsurlsessionconfiguration.backgroundsessionconfigurationwithidentifier(sessionproperties.identifier)     var backgroundsession = nsurlsession(configuration: configuration, delegate: delegate, delegatequeue: nil)     //myurlsession = nsurlsession(configuration: configuration, delegate: delegate, delegatequeue: nil)     var url = nsurlrequest(url: nsurl(string: surl)!)     var downloadtask = backgroundsession.downloadtaskwithrequest(url)      //downloadtask.cancel()      downloadtask.resume()  }

update when using different sessionid, download starts scratch. started download task runs still in background. wondering why can't resume download task using old sessionid without starting new download in parallel ?

the whole point of using download task downloads can continue if app isn't running or if crashes. don't need resume download. happening in separate background daemon. need re-create session using same id.

after re-create session, existing downloads automatically associated new session, , delegate methods called whenever task completes.

there's little bit of magic need implement handling background launches if app isn't running when download finishes. see url session programming guide details.


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