limit the number of concurrent downloads in AFURLSessionManager - ios

Question

Idea
I'm building files download manager using AFNetworking and I'm using AFURLSessionManager class. the app is suppose to download mp3 files from the server.
I was concerned about memory consuming, so I'm trying to limit the number of simultaneous downloads to 1.
I know that there is a NSOperationQueue property in AFURLSessionManager called operationQueue and it's limited to 1 operation at a time by default.so I'm adding my NSURLSessionDownloadTask to operationQueue.
the problem
the code isn't working. files is being downloaded simultaneously instead of one after another.
the code
// 1. build sessionManager and prepare some vars
// note: by testing i found that it's better to init NSURLSessionConfiguration with backgroundSessionConfigurationWithIdentifier for memory issues
NSURLSessionConfiguration *conf = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:#"special_Identifier"];
AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:conf];
NSURL *urlDocs = [[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory
inDomain:NSUserDomainMask
appropriateForURL:nil
create:NO
error:nil];
__block NSProgress *progress = Nil;
// 2. open sessionManager operation Queue and add this new download
[manager.operationQueue addOperationWithBlock:^{
// 2.1 init new download request
NSURLRequest *request = [[NSURLRequest alloc]initWithURL:[NSURL URLWithString:fileLink]];
// 2.2 creat a NSURLSessionDownloadTask
NSURLSessionDownloadTask *downloadTask = [self.downloadManager downloadTaskWithRequest:request progress:&progress
destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
return [urlDocs URLByAppendingPathComponent:fileName];
} completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
if (!error) {
NSLog(#"done: %#", filePath);
}else{
NSLog(#"error %#",error);
}
}];
// 2.3 start downloading
[downloadTask resume];
// 2.4 track downloading progress using KVO
[progress addObserver:self
forKeyPath:NSStringFromSelector(#selector(fractionCompleted))
options:NSKeyValueObservingOptionNew
context:(__bridge void *)(fileLink)];
}];

Answer 1

In AFNetworking 2 (and AFNetworking 3), you can init your AFHTTPSessionManager with an NSURLSessionConfiguration (use AFHTTPSessionManager initWithBaseURL:sessionConfiguration:). There you can specify the number of connections per host (HTTPMaximumConnectionsPerHost).
Sample:
NSURL *url = [NSURL URLWithString:#"myurl.net"];
NSURLSessionConfiguration *configuration = NSURLSessionConfiguration.defaultSessionConfiguration;
configuration.HTTPMaximumConnectionsPerHost = 1;
AFHTTPSessionManager *sessionManager = [[AFHTTPSessionManager alloc] initWithBaseURL:url sessionConfiguration:sessionConfiguration];
Documentation:
AFHTTPSessionManager: http://cocoadocs.org/docsets/AFNetworking/3.0.4/Classes/AFHTTPSessionManager.html#//api/name/initWithBaseURL:sessionConfiguration:
NSURLSessionConfiguration: https://developer.apple.com/library/ios/documentation/Foundation/Reference/NSURLSessionConfiguration_class/#//apple_ref/occ/instp/NSURLSessionConfiguration/HTTPMaximumConnectionsPerHost