iOS 8, XCode 6.3.2
I want to download multiple files serially.
In the wake of the Push notification, APP will start BackgroudDownload by NSURLSessionDownloadTask.
After the First BackgroudDownload process has been completed, APP want to start Second process, but Second BackgroudDownload process does not start.
Code is below
// This method is called by Push Notification
- (void)startBackgroundDownload
{
// Session
NSURLSessionConfiguration *configFirst = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:#"com.test.first"];
sessionFirst = [NSURLSession sessionWithConfiguration:configFirst delegate:self delegateQueue:nil];
NSURLSessionConfiguration *configSecond = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:#"com.test.second"];
sessionSecond = [NSURLSession sessionWithConfiguration:configSecond delegate:self delegateQueue:nil];
// Start First Download
NSURLRequest *requestFirst = [NSURLRequest requestWithURL:[NSURL URLWithString:#"http://xxxxx/first.zip"]];
NSURLSessionDownloadTask *downloadTaskFirst = [sessionFirst downloadTaskWithRequest:requestFirst];
[downloadTaskFirst resume];
}
// Finish Download
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
if (session == sessionFirst) {
NSURLRequest *requestSecond = [NSURLRequest requestWithURL:[NSURL URLWithString:#"http://xxxxx/second.zip"
NSURLSessionDownloadTask *downloadTaskSecond = [sessionSecond downloadTaskWithRequest:requestSecond];
[downloadTaskSecond resume];
} else if (session == sessionSecond) {
NSLog(#"all finish");
}
}
The First is successful, and the Second is fail (not start).
I want advice to pursue the cause.
Thank you for any help you can provide.
downloading task is divide in perfect part like as follow.
First make one array of zip files which you want to download.
Initialise session object
Write one method which can get URL and "startDownloading"
In delegate method (successful download) called unzip that file. remove first object of zip array and again called "startDownloading" method and its call until your array count is greater than zero
I hope you will understand what I want to explain here.
Related
Working on an IOS9 app that is doing a background URLSession in a controller that is a NSURLSessionDelegate. Here is how I start it:
self.session_data = [[NSMutableData alloc] init];
NSURL *url = [NSURL URLWithString:src];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSURLSessionConfiguration *backgroundConfigObject = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier: #"myBackgroundSessionIdentifier"];
self.session = [NSURLSession sessionWithConfiguration: backgroundConfigObject delegate: self delegateQueue: [NSOperationQueue mainQueue]];
self.download = [self.session dataTaskWithRequest: request ];
[self.download resume];
So far so good. I implement the three delegate methods. 'didReceiveData' is called first and I store the data.
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data{
NSLog(#"%s",__func__);
[self.session_data appendData:data];
}
Right after that 'didCompleteWithError' is called. The 'completionHandler' handler is never called.
What is confusing about 'didCompleteWithError' message is that the actual error object is nil. I have seen some similar unanswered questions. I am not leaving the controller/view while loading. Do I need to move that functionality into AppDelegate?
Apple doc said that didCompleteWithError report only client side error, otherwise is nil:
"Server errors are not reported through the error parameter. The only errors your delegate receives through the error parameter are client-side errors, such as being unable to resolve the hostname or connect to the host."
This is the link to the documentation.
If you want to check other errors like session's errors you have to implement session protocol delegate
- URLSession:didBecomeInvalidWithError:
For more details, see this answer
I've been using cURL to download about 1700+ files -- which total to about ~290MB -- in my iOS app. It takes about 5-7 minutes on my Internet connection to download all of them using cURL. But since not everyone has fast internet connection (especially when on the go), I decided to allow the files to be downloaded in the background, so that the user can do other things while waiting for the download to finish. This is where NSURLSession comes in.
Using NSURLSession, it takes about 20+ minutes on my Internet connection to download all of them while the app is in foreground. I don't mind it being slow when the app is in background, because I understand that it is up to the OS to schedule the downloads. But it's a problem when it's slow even when it's in foreground. Is this the expected behaviour? Is it because of the quantity of the files?
In case I'm not using NSURLSession correctly, here's a snippet of how I'm using it:
// Initialization
NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:#"<my-identifier>"];
sessionConfiguration.HTTPMaximumConnectionsPerHost = 40;
backgroundSession = [NSURLSession sessionWithConfiguration:sessionConfiguration
delegate:self
delegateQueue:nil];
// ...
// Creating the tasks and starting the download
for (int i = 0; i < 20 && queuedRequests.count > 0; i++) {
NSDictionary *requestInfo = [queuedRequests lastObject];
NSURLSessionDownloadTask *downloadTask = [backgroundSession downloadTaskWithURL:[NSURL URLWithString:requestInfo[#"url"]]];
ongoingRequests[#(downloadTask.taskIdentifier)] = requestInfo;
[downloadTask resume];
[queuedRequests removeLastObject];
NSLog(#"Begin download file %d/%d: %#", allRequests.count - queuedRequests.count, allRequests.count, requestInfo[#"url"]);
}
// ...
// Somewhere in (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
// After each download task is completed, grab a file to download from
// queuedRequests, and create another task
if (queuedRequests.count > 0) {
requestInfo = [queuedRequests lastObject];
NSURLSessionDownloadTask *newDownloadTask = [backgroundSession downloadTaskWithURL:[NSURL URLWithString:requestInfo[#"url"]]];
ongoingRequests[#(newDownloadTask.taskIdentifier)] = requestInfo;
[newDownloadTask resume];
[queuedRequests removeLastObject];
NSLog(#"Begin download file %d/%d: %#", allRequests.count - queuedRequests.count, allRequests.count, requestInfo[#"url"]);
}
I've also tried using multiple NSURLSession, but it's still slow. The reason I tried that is because when using cURL, I create multiple threads (around 20), and each thread will download a single file at a time.
It's also not possible for me to reduce the number of files by zipping it, because I need the app to be able to download individual files since I will update them from time to time. Basically, when the app starts, it will check if there are any files that have been updated, and only download those files. Since the files are stored in S3, and S3 doesn't have zipping service, I could not zip them into a single file on the fly.
As mentioned by Filip and Rob in the comments, the slowness is because when NSURLSession is initialized with backgroundSessionConfigurationWithIdentifier:, the download tasks will be executed in the background regardless if the app is in the foreground. So I solved this issue by having 2 instances of NSURLSession: one for foreground download, and one for background download:
NSURLSessionConfiguration *foregroundSessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
foregroundSessionConfig.HTTPMaximumConnectionsPerHost = 40;
foregroundSession = [NSURLSession sessionWithConfiguration:foregroundSessionConfig
delegate:self
delegateQueue:nil];
[foregroundSession retain];
NSURLSessionConfiguration *backgroundSessionConfig = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:#"com.terato.darknessfallen.BackgroundDownload"];
backgroundSessionConfig.HTTPMaximumConnectionsPerHost = 40;
backgroundSession = [NSURLSession sessionWithConfiguration:backgroundSessionConfig
delegate:self
delegateQueue:nil];
[backgroundSession retain];
When the app is switched to background, I simply call cancelByProducingResumeData: on each of the download tasks that's still running, and then pass it to downloadTaskWithResumeData::
- (void)switchToBackground
{
if (state == kDownloadManagerStateForeground) {
[foregroundSession getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
for (NSURLSessionDownloadTask *downloadTask in downloadTasks) {
[downloadTask cancelByProducingResumeData:^(NSData *resumeData) {
NSURLSessionDownloadTask *downloadTask = [backgroundSession downloadTaskWithResumeData:resumeData];
[downloadTask resume];
}];
}
}];
state = kDownloadManagerStateBackground;
}
}
Likewise, when the app is switched to foreground, I do the same but switched foregroundSession with backgroundSession:
- (void)switchToForeground
{
if (state == kDownloadManagerStateBackground) {
[backgroundSession getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
for (NSURLSessionDownloadTask *downloadTask in downloadTasks) {
[downloadTask cancelByProducingResumeData:^(NSData *resumeData) {
NSURLSessionDownloadTask *downloadTask = [foregroundSession downloadTaskWithResumeData:resumeData];
[downloadTask resume];
}];
}
}];
state = kDownloadManagerStateForeground;
}
}
Also, don't forget to call beginBackgroundTaskWithExpirationHandler: before calling switchToBackground when the app is switched to background. This is to ensure that the method is allowed to complete while in background. Otherwise, it will only be called once the app enters foreground again.
In my App I get JSON from a Web service. This JSON contains the urls of several files that I would like to download.
I want to download each file one by one (wait for the first download to finished until the second one starts and so an and so forth) using NSURLSessionDownloadTask. I would also like to keep track of the total bytes written so I can update UI.
Thanks a lot in advance !
NSURLSessionDownloadTask's as you well know do not play very nicely with NSOperationQueues unlike their counterpart the NSURLConnection (where it could be encapsulated inside an NSOperation).
One option would be to add all your urls to an array, and then inside the completionHandler of the task, simply queue the next item.
So you might create your tasks in a loop, call a progressBlock inside each tasks completion handler, store the tasks in an array, and queue the next task inside each tasks completion handler:
- (void)addRequestsWithURLs:(NSArray *)urls
progressBlock:(void (^)(NSUInteger numberOfFinishedOperations, NSUInteger totalNumberOfOperations, NSURLSessionDownloadTask *task,NSURL *location, NSURLResponse *response, NSError *error))progressBlock {
__block NSUInteger numberOfFinishedOperations = 0;
NSUInteger totalNumberOfOperations = [urls count];
for (NSString *url in urls) {
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];
__block NSURLSessionDownloadTask *task = [self.session downloadTaskWithRequest:request
completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {
//downloadFileSomewhere
++numberOfFinishedOperations;
if (progressBlock) {
progressBlock(numberOfFinishedOperations, totalNumberOfOperations,task,destination != nil ? [NSURL fileURLWithPath:destination] : nil,response,error);
}
//queueNext
[self processCompletedTask:task];
}];
//stores an array of NSURLSessionTasks
[self.tasksWaitingToBeQueued addObject:task];
}
}
- (void)processCompletedTask:(NSURLSessionTask *)completedTask {
//clean up and queue next one
[self.tasksWaitingToBeQueued removeObject:completedTask];
nextTask = [self.tasksWaitingToBeQueued firstObject];
if (nextTask) {
[nextTask resume];
}
}
NOTE
In this example I show progress as the number of tasks completed and not the number of bytes, this is the recommended approach (its also simpler). To indicate progress using bytes you would need to know the total number of bytes to download beforehand (since you want to show a progress bar) and also implement the NSURLSession delegate and monitor the progress of each task, capture the bytes downloaded and update your block. If your server doesn't tell you the total number of bytes then you would probably need to do a HEAD request for every resource and aggregate the sizes. Personally this solution is way to complicated for what could simply be resolved by indicating progress as the number of files downloaded.
To achieve this might look something like this:
- (void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didWriteData:(int64_t)bytesWritten
totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
self.totalBytesWritten += totalBytesWritten;
NSUInteger totalProgressSoFar = self.totalBytesWritten;
NSUInteger totalExpectedBytes = self.totalExpectedBytes;
//you would need to capture some progress block locally - beware of retain cycles
self.progressBlock(totalProgressSoFar/totalExpectedBytes)
}
when you finish you should set the progressBlock to nil to prevent any retain cycles.
I have big trouble with NSURLSession when i'll terminate the App.
I have downloaded the apple sample:
https://developer.apple.com/library/ios/samplecode/SimpleBackgroundTransfer/Introduction/Intro.html
on Apple reference.
When i start download the file download correctly.
When i enter in background the download continues to.
When i terminate the application and i restart the app the application enter in:
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
And i catch this error:
The operation couldn't be completed. (NSURLErrorDomain error -999.)
It seems that i cannot restore download when app has been terminated. It's correct?For proceed with download i must leave application active in background?
Thank you
Andrea
A couple of observations:
Error -999 is kCFURLErrorCancelled.
If you are using NSURLSessionDownloadTask, you can download those in the background using background session configuration, e.g.
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:kBackgroundIdentifier];
NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
If not using background session (e.g. you have to use data task, for example), you can use beginBackgroundTaskWithExpirationHandler to request a little time for the app the finish requests in the background before the app terminates.
Note, when using background sessions, your app delegate must respond to handleEventsForBackgroundURLSession, capturing the completion handler that it will call when appropriate (e.g., generally in URLSessionDidFinishEventsForBackgroundURLSession).
How did you "terminate the app"? If you manually kill it (by double tapping on home button, holding down on icon for running app, and then hitting the little red "x"), that will not only terminate the app, but it will stop background sessions, too. Alternatively, if the app crashes or if it is simply jettisoned because foreground apps needed more memory, the background session will continue.
Personally, whenever I want to test background operation after app terminates, I have code in my app to crash (deference nil pointer, like Apple did in their WWDC video introduction to NSURLSession). Clearly you'd never do that in a production app, but it's hard to simulate the app being jettisoned due to memory constraints, so deliberately crashing is a fine proxy for that scenario.
i insert this new lines of code:
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
BLog();
NSInteger errorReasonNum = [[error.userInfo objectForKey:#"NSURLErrorBackgroundTaskCancelledReasonKey"] integerValue];
if([error.userInfo objectForKey:#"NSURLErrorBackgroundTaskCancelledReasonKey"] &&
(errorReasonNum == NSURLErrorCancelledReasonUserForceQuitApplication ||
errorReasonNum == NSURLErrorCancelledReasonBackgroundUpdatesDisabled))
{
NSData *resumeData = error.userInfo[NSURLSessionDownloadTaskResumeData];
if (resumeData) {
// resume
NSURL *downloadURL = [NSURL URLWithString:DownloadURLString];
NSURLRequest *request = [NSURLRequest requestWithURL:downloadURL];
if (!self.downloadTask) {
self.downloadTask = [self.session downloadTaskWithRequest:request];
}
[self.downloadTask resume];
if (!_session){
[[_session downloadTaskWithResumeData:resumeData]resume];
}
}
}
}
It catch NSURLErrorCancelledReasonUserForceQuitApplication but when the application try to [[_session downloadTaskWithResumeData:resumeData]resume]
reenter again in:
(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
and give me again -999 error.
I use this configuration
- (NSURLSession *)backgroundSession
{
/*
Using disptach_once here ensures that multiple background sessions with the same identifier are not created in this instance of the application. If you want to support multiple background sessions within a single process, you should create each session with its own identifier.
*/
static NSURLSession *session = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfiguration:#"com.example.apple-samplecode.SimpleBackgroundTransfer.BackgroundSession"];
session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
});
return session;
}
let me explain what i mean with "terminate the app" (in ios8):
double tap on home button
swipe on my open app.
app disappear from open app list
relaunch app.
When i reopen the app i enter into callback with error
The operation couldn't be completed. (NSURLErrorDomain error -999.)
There is something that i can't understand. This behaviour make me crazy! :-(
I'm a bit confuse of how to take advantage of the new iOS 7 NSURLSession background transfers features and AFNetworking (versions 2 and 3).
I saw the WWDC 705 - What’s New in Foundation Networking session, and they demonstrated background download that continues after the app terminated or even crashes.
This is done using the new API application:handleEventsForBackgroundURLSession:completionHandler: and the fact that the session's delegate will eventually get the callbacks and can complete its task.
So I'm wondering how to use it with AFNetworking (if possible) to continue downloading in background.
The problem is, AFNetworking conveniently uses block based API to do all the requests, but if the app terminated or crashes those block are also gone. So how can I complete the task?
Or maybe I'm missing something here...
Let me explain what I mean:
For example my app is a photo messaging app, lets say that I have a PhotoMessage object that represent one message and this object has properties like
state - describe the state of the photo download.
resourcePath - the path to the final downloaded photo file.
So when I get a new message from the server, I create a new PhotoMessage object, and start downloading its photo resource.
PhotoMessage *newPhotoMsg = [[PhotoMessage alloc] initWithInfoFromServer:info];
newPhotoMsg.state = kStateDownloading;
self.photoDownloadTask = [[BGSessionManager sharedManager] downloadTaskWithRequest:request progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
NSURL *filePath = // some file url
return filePath;
} completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
if (!error) {
// update the PhotoMessage Object
newPhotoMsg.state = kStateDownloadFinished;
newPhotoMsg.resourcePath = filePath;
}
}];
[self.photoDownloadTask resume];
As you can see, I use the completion block to update that PhotoMessage object according to the response I get.
How can I accomplish that with a background transfer? This completion block won't be called and as a result, I can't update the newPhotoMsg.
A couple of thoughts:
You have to make sure you do the necessary coding outlined in the Handling iOS Background Activity section of the URL Loading System Programming Guide says:
If you are using NSURLSession in iOS, your app is automatically relaunched when a download completes. Your app’s application:handleEventsForBackgroundURLSession:completionHandler: app delegate method is responsible for recreating the appropriate session, storing a completion handler, and calling that handler when the session calls your session delegate’s URLSessionDidFinishEventsForBackgroundURLSession: method.
That guide shows some examples of what you can do. Frankly, I think the code samples discussed in the latter part of the WWDC 2013 video What’s New in Foundation Networking are even more clear.
The basic implementation of AFURLSessionManager will work in conjunction with background sessions if the app is merely suspended (you'll see your blocks called when the network tasks are done, assuming you've done the above). But as you guessed, any task-specific block parameters that are passed to the AFURLSessionManager method where you create the NSURLSessionTask for uploads and downloads are lost "if the app terminated or crashes."
For background uploads, this is an annoyance (as your task-level informational progress and completion blocks you specified when creating the task will not get called). But if you employ the session-level renditions (e.g. setTaskDidCompleteBlock and setTaskDidSendBodyDataBlock), that will get called properly (assuming you always set these blocks when you re-instantiate the session manager).
As it turns out, this issue of losing the blocks is actually more problematic for background downloads, but the solution there is very similar (do not use task-based block parameters, but rather use session-based blocks, such as setDownloadTaskDidFinishDownloadingBlock).
An alternative, you could stick with default (non-background) NSURLSession, but make sure your app requests a little time to finish the upload if the user leaves the app while the task is in progress. For example, before you create your NSURLSessionTask, you can create a UIBackgroundTaskIdentifier:
UIBackgroundTaskIdentifier __block taskId = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^(void) {
// handle timeout gracefully if you can
[[UIApplication sharedApplication] endBackgroundTask:taskId];
taskId = UIBackgroundTaskInvalid;
}];
But make sure that the completion block of the network task correctly informs iOS that it is complete:
if (taskId != UIBackgroundTaskInvalid) {
[[UIApplication sharedApplication] endBackgroundTask:taskId];
taskId = UIBackgroundTaskInvalid;
}
This is not as powerful as a background NSURLSession (e.g., you have a limited amount of time available), but in some cases this can be useful.
Update:
I thought I'd add a practical example of how to do background downloads using AFNetworking.
First define your background manager.
//
// BackgroundSessionManager.h
//
// Created by Robert Ryan on 10/11/14.
// Copyright (c) 2014 Robert Ryan. All rights reserved.
//
#import "AFHTTPSessionManager.h"
#interface BackgroundSessionManager : AFHTTPSessionManager
+ (instancetype)sharedManager;
#property (nonatomic, copy) void (^savedCompletionHandler)(void);
#end
and
//
// BackgroundSessionManager.m
//
// Created by Robert Ryan on 10/11/14.
// Copyright (c) 2014 Robert Ryan. All rights reserved.
//
#import "BackgroundSessionManager.h"
static NSString * const kBackgroundSessionIdentifier = #"com.domain.backgroundsession";
#implementation BackgroundSessionManager
+ (instancetype)sharedManager {
static id sharedMyManager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedMyManager = [[self alloc] init];
});
return sharedMyManager;
}
- (instancetype)init {
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:kBackgroundSessionIdentifier];
self = [super initWithSessionConfiguration:configuration];
if (self) {
[self configureDownloadFinished]; // when download done, save file
[self configureBackgroundSessionFinished]; // when entire background session done, call completion handler
[self configureAuthentication]; // my server uses authentication, so let's handle that; if you don't use authentication challenges, you can remove this
}
return self;
}
- (void)configureDownloadFinished {
// just save the downloaded file to documents folder using filename from URL
[self setDownloadTaskDidFinishDownloadingBlock:^NSURL *(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, NSURL *location) {
if ([downloadTask.response isKindOfClass:[NSHTTPURLResponse class]]) {
NSInteger statusCode = [(NSHTTPURLResponse *)downloadTask.response statusCode];
if (statusCode != 200) {
// handle error here, e.g.
NSLog(#"%# failed (statusCode = %ld)", [downloadTask.originalRequest.URL lastPathComponent], statusCode);
return nil;
}
}
NSString *filename = [downloadTask.originalRequest.URL lastPathComponent];
NSString *documentsPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
NSString *path = [documentsPath stringByAppendingPathComponent:filename];
return [NSURL fileURLWithPath:path];
}];
[self setTaskDidCompleteBlock:^(NSURLSession *session, NSURLSessionTask *task, NSError *error) {
if (error) {
// handle error here, e.g.,
NSLog(#"%#: %#", [task.originalRequest.URL lastPathComponent], error);
}
}];
}
- (void)configureBackgroundSessionFinished {
typeof(self) __weak weakSelf = self;
[self setDidFinishEventsForBackgroundURLSessionBlock:^(NSURLSession *session) {
if (weakSelf.savedCompletionHandler) {
weakSelf.savedCompletionHandler();
weakSelf.savedCompletionHandler = nil;
}
}];
}
- (void)configureAuthentication {
NSURLCredential *myCredential = [NSURLCredential credentialWithUser:#"userid" password:#"password" persistence:NSURLCredentialPersistenceForSession];
[self setTaskDidReceiveAuthenticationChallengeBlock:^NSURLSessionAuthChallengeDisposition(NSURLSession *session, NSURLSessionTask *task, NSURLAuthenticationChallenge *challenge, NSURLCredential *__autoreleasing *credential) {
if (challenge.previousFailureCount == 0) {
*credential = myCredential;
return NSURLSessionAuthChallengeUseCredential;
} else {
return NSURLSessionAuthChallengePerformDefaultHandling;
}
}];
}
#end
Make sure app delegate saves completion handler (instantiating the background session as necessary):
- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler {
NSAssert([[BackgroundSessionManager sharedManager].session.configuration.identifier isEqualToString:identifier], #"Identifiers didn't match");
[BackgroundSessionManager sharedManager].savedCompletionHandler = completionHandler;
}
Then start your downloads:
for (NSString *filename in filenames) {
NSURL *url = [baseURL URLByAppendingPathComponent:filename];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[[[BackgroundSessionManager sharedManager] downloadTaskWithRequest:request progress:nil destination:nil completionHandler:nil] resume];
}
Note, I don't supply any of those task related blocks, because those aren't reliable with background sessions. (Background downloads proceed even after the app is terminated and these blocks have long disappeared.) One must rely upon the session-level, easily recreated setDownloadTaskDidFinishDownloadingBlock only.
Clearly this is a simple example (only one background session object; just saving files to the docs folder using last component of URL as the filename; etc.), but hopefully it illustrates the pattern.
It shouldn't make any difference whether or not the callbacks are blocks or not. When you instantiate an AFURLSessionManager, make sure to instantiate it with NSURLSessionConfiguration backgroundSessionConfiguration:. Also, make sure to call the manager's setDidFinishEventsForBackgroundURLSessionBlock with your callback block - this is where you should write the code typically defined in NSURLSessionDelegate's method:
URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session. This code should invoke your app delegate's background download completion handler.
One word of advice regarding background download tasks - even when running in the foreground, their timeouts are ignored, meaning you could get "stuck" on a download that's not responding. This is not documented anywhere and drove me crazy for some time. The first suspect was AFNetworking but even after calling NSURLSession directly, the behaviour remained the same.
Good luck!
AFURLSessionManager
AFURLSessionManager creates and manages an NSURLSession object based on a specified NSURLSessionConfiguration object, which conforms to <NSURLSessionTaskDelegate>, <NSURLSessionDataDelegate>, <NSURLSessionDownloadDelegate>, and <NSURLSessionDelegate>.
link to documentation here documentation