How to download large file in background using AFNetworking 3.0 and present local notification when session completes all the tasks

Question

I am trying to download large video file in my application using AFNetworking 3.0. I couldn't find any specific document regarding how to download file in background using AFNetworking.

I know AFNetworking uses AFURLSessionManager and AFHTTPSessionManager which itself implements all the delegates of NSURLSession.

What I did so far is, created a backgroundSessionConfugaration and started a file to download using this.

self.manager = [[AFHTTPSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:bgDownloadSessionIdentifier]];

[self.manager downloadTaskWithRequest:request progress:nil destination:nil completionHandler:nil];

When download starts, I put my application in background. What I found so far is app is running in background till 20 mins and download was successful. But application:handleEventsForBackgroundURLSession in appDelegate is not called, so my setDidFinishEventsForBackgroundURLSessionBlock is also not getting called.

I want to show a notification only when setDidFinishEventsForBackgroundURLSessionBlock is called.

When I initialise manager using this. (instead of backgroundSessionConfiguration)

self.manager = [AFHTTPSessionManager manager];

Still app is able to download entire file after 20 mins in background.

My problem is why application is running till 20 mins and completed the download. As ideally iOS should kill the app after 10 mins. Also why application:handleEventsForBackgroundURLSession is not getting called after session completion.

I've already referred this AFNetworking 2.0 and background transfers, but it seems not working for me.

Background Modes from capabilities is either ON or OFF doesn't affect anything in my application.

Please help me or suggest me what I am doing wrong here.

I've uploaded the example code here. https://www.dropbox.com/s/umwicuta2qzd3k1/RSNetworkKitExample.zip?dl=0

AppDelegate.m

-(void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler {

  NSLog(@"===== background session completed in AppDelegate ===== ");

  if([identifier isEqualToString:bgDownloadSessionIdentifier]){
      [RSDownloadManager sharedManager].backgroundSessionCompletionHandler = completionHandler;
  }
}

====================================================

ViewController.m


- (IBAction)downloadVideoInBackground:(id)sender {

  NSString *videoURL = @"http://videos1.djmazadownload.com/mobile/mobile_videos/Tum%20Saath%20Ho%20(Tamasha)%20(DJMaza.Info).mp4";

 [RSDownloadManager sharedManager].backgroundSessionCompletionHandler = ^{

    NSLog(@"===== background session completed in ViewController ===== ");

    UILocalNotification* localNotification = [[UILocalNotification alloc] init];
    localNotification.alertBody = @"Download Complete!";
    localNotification.alertAction = @"Background Transfer Download!";

    //On sound
    localNotification.soundName = UILocalNotificationDefaultSoundName;

    //increase the badge number of application plus 1
    localNotification.applicationIconBadgeNumber = [[UIApplication sharedApplication] applicationIconBadgeNumber] + 1;

    [[UIApplication sharedApplication] presentLocalNotificationNow:localNotification];

};

  [[RSDownloadManager sharedManager] downloadInBackgroundWithURL:videoURL downloadProgress:^(NSNumber *progress) {

     NSLog(@"Video download progress %.2f", [progress floatValue]);

  } success:^(NSURLResponse *response, NSURL *filePath) {

     NSLog(@"Video download completed at Path %@", filePath);

  } andFailure:^(NSError *error) {

     NSLog(@"Error in video download %@", error.description);
  }];

}

====================================================

RSDownloadManager.h


#import <Foundation/Foundation.h>
#import "AFHTTPSessionManager.h"

static NSString *bgDownloadSessionIdentifier = @"com.RSNetworkKit.bgDownloadSessionIdentifier";

@interface RSDownloadManager : NSObject

@property (nonatomic, strong) AFHTTPSessionManager *manager;

@property (nonatomic, copy) void (^backgroundSessionCompletionHandler)(void);

+(instancetype)sharedManager;

-(NSURLSessionDownloadTask *)downloadInBackgroundWithURL:(NSString *)urlString downloadProgress:(void (^)(NSNumber *progress))progressBlock success:(void (^)(NSURLResponse *response, NSURL *filePath))completionBlock andFailure:(void (^)(NSError *error))failureBlock;

@end

====================================================

RSDownloadManager.m


@implementation RSDownloadManager

#pragma mark - Singleton instance
+(instancetype)sharedManager
{
   static RSDownloadManager *_downloadManager = nil;
   static dispatch_once_t token;

   dispatch_once(&token, ^{

     if (!_downloadManager) {
        _downloadManager = [[self alloc] init];
     }
  });
   return _downloadManager;
}

#pragma mark - Init with Session Configuration

-(void)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration {
   self.manager = [[AFHTTPSessionManager alloc] initWithSessionConfiguration:configuration];

   //self.manager = [AFHTTPSessionManager manager];
}


#pragma mark- Handle background session completion

- (void)configureBackgroundSessionCompletion {
  typeof(self) __weak weakSelf = self;

  [self.manager setDidFinishEventsForBackgroundURLSessionBlock:^(NSURLSession *session) {

     if (weakSelf.backgroundSessionCompletionHandler) {
         weakSelf.backgroundSessionCompletionHandler();
         weakSelf.backgroundSessionCompletionHandler = nil;
     }
  }];
}


#pragma mark- download in background request Method

-(NSURLSessionDownloadTask *)downloadInBackgroundWithURL:(NSString *)urlString downloadProgress:(void (^)(NSNumber *))progressBlock success:(void (^)(NSURLResponse *, NSURL *))completionBlock andFailure:(void (^)(NSError *))failureBlock {

  /* initialise session manager with background configuration */

  if(!self.manager){
     [self initWithSessionConfiguration:[NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:bgDownloadSessionIdentifier]];
  }

  [self configureBackgroundSessionCompletion];

  /* Create a request from the url */
  NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlString]];

  NSURLSessionDownloadTask *downloadTask = [self.manager downloadTaskWithRequest:request progress:^(NSProgress * _Nonnull downloadProgress) {

     if(progressBlock) {
         progressBlock ([NSNumber numberWithDouble:downloadProgress.fractionCompleted]);
     }

 } destination:^NSURL * _Nonnull(NSURL * _Nonnull targetPath, NSURLResponse * _Nonnull response) {

     NSURL *documentsDirectoryURL = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:NO error:nil];
     return [documentsDirectoryURL URLByAppendingPathComponent:[response suggestedFilename]];

 } completionHandler:^(NSURLResponse * _Nonnull response, NSURL * _Nullable filePath, NSError * _Nullable error) {

    if(error) {
        if(failureBlock) {
            failureBlock (error);
        }
    }
    else {
        if(completionBlock) {
            completionBlock (response, filePath);
        }
    }

 }];

  [downloadTask resume];

  return downloadTask;
 }

Answer 1

This delegate methods will not get called sometimes ,

• If application is already running when task completes.
• application terminated by home button.
• If you fail to start a background NSURLSession with the same identifier.

Note : this behaves differently on simulator, so please check on real device.

Answer 2

Why you just no replace local notification block to success block in your downloadInBackgroundWithURL:downloadProgress: fucntion? Method in AppDelegate realy not called. And you need register your notification

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.

    if ([UIApplication instancesRespondToSelector:@selector(registerUserNotificationSettings:)]){
         [application registerUserNotificationSettings:[UIUserNotificationSettings settingsForTypes:UIUserNotificationTypeAlert|UIUserNotificationTypeBadge|UIUserNotificationTypeSound categories:nil]];
    }

    return YES;
}

And for local notification add fire date and time zone:

    UILocalNotification* localNotification = [[UILocalNotification alloc] init];
    localNotification.alertBody = @"Download Complete!";
    localNotification.alertAction = @"Background Transfer Download!";
    [localNotification setFireDate:[NSDate dateWithTimeIntervalSinceNow:1]];
    [localNotification setTimeZone:[NSTimeZone  defaultTimeZone]];
    //On sound
    localNotification.soundName = UILocalNotificationDefaultSoundName;

    //increase the badge number of application plus 1
    localNotification.applicationIconBadgeNumber = [[UIApplication sharedApplication] applicationIconBadgeNumber] + 1;

    [[UIApplication sharedApplication] presentLocalNotificationNow:localNotification];

Now it works. Cheers.