Checking which kind of NSURLSessionTask occurred

Question

I seem to be running into trouble. For some reason, If I try to check the class type of my NSURLSessionTask objects, it doesn't work at all. If I check their taskDescription properties, this works of course if I set them before initiating the task. I would just like to know why the below code doesn't work for me. I appreciate any help offered!

- (void)uploadIt
{
    NSURLSessionConfiguration *defaultConfigObject = [NSURLSessionConfiguration ephemeralSessionConfiguration];
    defaultConfigObject.timeoutIntervalForResource = 15.0;
    defaultConfigObject.requestCachePolicy = NSURLRequestReloadIgnoringLocalAndRemoteCacheData;

    NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration:defaultConfigObject delegate:self delegateQueue:[NSOperationQueue mainQueue]];

    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

    NSURLSessionUploadTask *uploadTask = [defaultSession uploadTaskWithRequest:someRequest fromData:body];
    [uploadTask resume];
}  

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;

    if (self.uploadResponseData)
    {
        NSDictionary *d = [NSJSONSerialization JSONObjectWithData:self.uploadResponseData options:kNilOptions error:nil];
        NSLog(@"Dict: %@",d);
    }

    if ([task isKindOfClass:[NSURLSessionDownloadTask class]])
    {
        // Not called
    }
    else if ([task isKindOfClass:[NSURLSessionUploadTask class]])
    {
        // Not called
    }
}

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
    if (!self.uploadResponseData)
    {
        self.uploadResponseData = [NSMutableData dataWithData:data];
    }
    else
    {
        [self.uploadResponseData appendData:data];
    }
}

Answer 1

My experience with this has been in the context of app-in-the-background NSURLSessionTasks. These get serialized to disk, there's a deamon involved, and my experience is that any class-based finagling didn't work too well in that context.

Particularly, I was trying to subclass NSURLSessionTask, but what came back in the -didComplete:... call was not an instance of that subclass.

I've come to think of NSURLSessionTask as a facade, or part of a "class cluster", and tried to be more careful about it.

If you need to mark a task as a particular type, you store whatever you like in the .description. I can confirm that info survives background serialization nicely.

Answer 2

I can't reproduce the issue from the code you've posted. I made a minimal example from your code, just creating a single-view application from the standard Xcode template, then using this as the view controller:

ViewController.h:

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController <NSURLSessionDelegate, NSURLSessionTaskDelegate>

@end

ViewController.m:

#import "ViewController.h"

@interface ViewController ()


@end

@implementation ViewController

 1. (void)viewDidLoad {
    [super viewDidLoad];
    [self uploadIt];
}

 2. (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

 3. (void)uploadIt
{
    NSURLSessionConfiguration *defaultConfigObject = [NSURLSessionConfiguration ephemeralSessionConfiguration];
    defaultConfigObject.timeoutIntervalForResource = 15.0;
    defaultConfigObject.requestCachePolicy = NSURLRequestReloadIgnoringLocalAndRemoteCacheData;

    NSURLSession *defaultSession = [NSURLSession sessionWithConfiguration:defaultConfigObject delegate:self delegateQueue:[NSOperationQueue mainQueue]];

    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;

    NSURLRequest* someRequest = [NSURLRequest requestWithURL: [NSURL URLWithString:@"http://example.com"]];
    NSData* body = [@"Fake body" dataUsingEncoding:NSUTF8StringEncoding];

    NSURLSessionUploadTask *uploadTask = [defaultSession uploadTaskWithRequest:someRequest fromData:body];
    [uploadTask resume];
}

-(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
    NSLog(@"Completed.");

    if ([task isKindOfClass:[NSURLSessionDownloadTask class]])
    {
        NSLog(@"The task was a download task");
    }
    else if ([task isKindOfClass:[NSURLSessionUploadTask class]])
    {
        NSLog(@"The task was an upload task");
    }
}
@end

The result was the following:

2014-07-02 17:57:28.002 24500545_nsurlsession_classes[22470:1250475] Completed. 2014-07-02 17:57:48.631 24500545_nsurlsession_classes[22470:1250475] The task was an upload task

(Are you certain you're logging correctly? What do you see if you set a breakpoint in your delegate method and step through the code? What does p task tell you in lldb?)