I'm creating a task to download an image in the background inside a function and I have a notification object in the same context. I want to retrieve this notification object when the delegate didFinishDownloadingToURL is called. Is there any way I can do this?
I create a task like this:
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:#"imageDownloadSession"];
[sessionConfig setDiscretionary:YES];
[sessionConfig setSessionSendsLaunchEvents:YES];
NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfig delegate:self delegateQueue:nil];
NSURLSessionDownloadTask *getImageTask = [session downloadTaskWithURL:notification.imageRemoteURL];
And this is my delegate:
-(void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location {
// I want to access the notification object here
}
You can simply store in the notification in a property in the class that you are using as NSURLSessionDownloadDelegate. So when downloadTaskWithURL is called you can access that property.
Alternatively you can create an other class that holds the notification as an instance property and acts as the delegate. An if you have multiple download tasks you can keep them in an array.
For example:
...
self.downloadDelegate = [[SessionDownloadDelegate alloc] init];
downloadDelegate.notification = notification
//Now use the downloadDelegate instead of self
NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfig delegate:downloadDelegate delegateQueue:nil];
...
#interface SessionDownloadDelegate: NSObject<NSURLSessionDownloadDelegate>
#property (strong, nonatomic) NSObject *notification;
#end
#implementation SessionDownloadDelegate
- (void)URLSession:(nonnull NSURLSession *)session downloadTask:(nonnull NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(nonnull NSURL *)location {
// access the notification object
// self.notification
}
#end
I am using NSURLSession to download a large video file in background. In this iOS application I implemented pause, resume and stop downloading feature.
Here is my code :
in .h
#property (nonatomic, strong) NSURLSessionDownloadTask *downloadTask;
#property (nonatomic, strong) NSURLSession *session;
in .m
NSURLSessionConfiguration *sessionConfiguration;
float ver = [[[UIDevice currentDevice] systemVersion] floatValue];
if(ver >= 8)
{
sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:#"sessionID"];
}
else
{
sessionConfiguration = [NSURLSessionConfiguration backgroundSessionConfiguration:#"sessionID"];
}
sessionConfiguration.HTTPMaximumConnectionsPerHost = 1;
self.session = [NSURLSession sessionWithConfiguration:sessionConfiguration
delegate:self
delegateQueue:nil];
For stop downloading I am using this method:
- (void)stopDownloading:(id)sender {
// Cancel the task.
[self.fdi.downloadTask cancel];
}
It works quite well with a large amount of files, but there is an inconvenience. When I stop downloading then Memory which is used in downloading is not released so the application size is continuously for stopped downloading tasks.
Try using
[self.session invalidateAndCancel];
as Per documentation
It will cancels all outstanding tasks and then invalidates the session.
Also, You can fetch the cache directory and then by using a loop or something fetch and remove folder and data inside.
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.
I created a simple NSURLSessionDownloadTask to download from a URL, with its class having the NSURLSession delegates:
#interface DownloadManager : NSObject <NSURLSessionDataDelegate, NSURLSessionDelegate, NSURLSessionDownloadDelegate, NSURLSessionTaskDelegate>
//...
NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
[sessionConfiguration setTimeoutIntervalForRequest:30.0];
[sessionConfiguration setTimeoutIntervalForResource:60.0];
NSURLSession *session = [NSURLSession sessionWithConfiguration:sessionConfiguration];
NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithURL:self.url];
[downloadTask resume];
However, I could not find a protocol method that listens to the download task timing out. Is there a way to listen to the timeout (ex. - I wanted to close a progress dialog box when 30.0 seconds have passed and no data is still received)
I've already scavenged Google but haven't found any information so far, so I'll leave this question here while I search for more info.
Thanks so much!
The timeout is one of the errors NSURLSession will give you in completionHandler block. It's NSURLErrorTimedOut = -1001.
in delegate method
- URLSession:task:didCompleteWithError:
check the NSError if it's NSURLErrorTimedOut do what you want
https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_Constants/#//apple_ref/doc/constant_group/URL_Loading_System_Error_Codes
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