How can I cast my NSURLSessionDownloadTask to my custom NSURLSessionDownloadTask (inheritance)? - objective-c

Question

I have created a custom NSURLSessionDownloadTask named VJSessionTask and I have just added some custom things like a type (enum) and a custom object (id):
#interface VJSessionTask : NSURLSessionDownloadTask
typedef enum types
{
LS, LSH, DL, UL, RM, TH
} type;
#property enum types type;
#property (strong, nonatomic) id customObject;
#property (strong, nonatomic) NSString *progressNotif;
#property (strong, nonatomic) NSString *doneNotif;
#property (strong, nonatomic) NSURL *tmpFile;
#end
And when I do this:
VJSessionTask *taskSession = (VJSessionTask *)[self.prioritySession downloadTaskWithRequest:listFileRequest];
// init taskSession with its type
taskSession.type = LS;
I get this error:
-[__NSCFLocalDownloadTask setType:]: unrecognized selector sent to instance 0x1556198f0
Then I come to you as I don't understand or I don't know how to do that...
Thank you in advance ;)

Answer 1

NSURLSessionTasks are not strictly speaking subclass-able unfortunately. This is evident in that the system can queue a data task and return a NSCFLocalDownloadTask (presumably meaning that the task will return its content from the cache).
The best way to go about doing this is to borrow on from the architectural decision of AFNetworking and have individual taskDelegates that monitor all the responses an individual task works on. Then when you want to find the data relating to a task you can query your dictionary of taskDelegates. Each task has a unique identifier that you can use to key your dictionary with.
In AFNetworking you can see the taskDelegate is defined as follows:
#interface AFURLSessionManagerTaskDelegate : NSObject <NSURLSessionTaskDelegate, NSURLSessionDataDelegate, NSURLSessionDownloadDelegate>
#property (nonatomic, weak) AFURLSessionManager *manager;
#property (nonatomic, strong) NSMutableData *mutableData;
#property (nonatomic, strong) NSProgress *progress;
#property (nonatomic, copy) NSURL *downloadFileURL;
#property (nonatomic, copy) AFURLSessionDownloadTaskDidFinishDownloadingBlock downloadTaskDidFinishDownloading;
#property (nonatomic, copy) AFURLSessionTaskCompletionHandler completionHandler;
#end
#implementation AFURLSessionManagerTaskDelegate
and subsequently retrieved as follows:
- (AFURLSessionManagerTaskDelegate *)delegateForTask:(NSURLSessionTask *)task {
NSParameterAssert(task);
AFURLSessionManagerTaskDelegate *delegate = nil;
[self.lock lock];
delegate = self.mutableTaskDelegatesKeyedByTaskIdentifier[#(task.taskIdentifier)];
[self.lock unlock];
return delegate;
}
See this post for more info