App/CourierTestApp/ViewController.m

#import "ViewController.h"
#import "AppDelegate.h"

#import <Courier/Courier.h>

static NSString * const TestTaskGroup1 = @"TestTaskGroup1";

static NSString * const TestTaskGroup2 = @"TestTaskGroup2";

@interface ViewController ()

@property (nonatomic, strong) CRSessionController *sessionController;

@property (nonatomic, weak) IBOutlet UIImageView *imageView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    configuration.HTTPMaximumConnectionsPerHost = 1;
    configuration.URLCache = nil;
    _sessionController = [CRSessionController sessionControllerWithConfiguration:configuration];
    
    [_sessionController setReachabilityStatusChangeBlock:^(NetworkStatus status) {
        if (status == NotReachable) {
            NSLog(@"Not reachable!");
        } else {
            NSLog(@"Reachable!");
        }
    }];
    
    [_sessionController startReachabilityMonitoring];
}

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

#pragma mark - IBAction

- (IBAction)startNetworkRequests:(id)sender {
    for (NSInteger i = 0; i < 10; i++) {
        BOOL even = i % 2;
        if (even) {
            [self startImageDownloadTaskInTaskGroup:TestTaskGroup1];
        } else {
            [self startImageDownloadTaskInTaskGroup:TestTaskGroup2];
        }
    }
}

- (IBAction)startNetworkRequestsOnAnotherThread:(id)sender {
    for (NSInteger i = 0; i < 10; i++) {
        BOOL even = i % 2;
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
            if (even) {
                [self startImageDownloadTaskInTaskGroup:TestTaskGroup1];
            } else {
                [self startImageDownloadTaskInTaskGroup:TestTaskGroup2];
            }
        });
    }
}

- (IBAction)stopNetworkRequests:(id)sender {
    [self.sessionController cancelTasksInGroup:TestTaskGroup1];
    [self.sessionController cancelTasksInGroup:TestTaskGroup2];
}

- (IBAction)nilSessionController:(id)sender {
    @autoreleasepool {
        [self.sessionController.session invalidateAndCancel];
        self.sessionController = nil;
    }
}

- (IBAction)printHasTasks:(id)sender {
    NSLog(@"Has tasks %i", [self.sessionController hasTasksInGroup:TestTaskGroup1
                                                         withState:NSURLSessionTaskStateRunning]);
}

#pragma mark - 

- (void)startImageDownloadTaskInTaskGroup:(NSString *)taskGroup {
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://static.fjcdn.com/pictures/Space_03b120_799520.jpg"]];
    NSURLSessionDataTask *task =
    [self.sessionController dataTaskForRequest:request
                                     taskGroup:taskGroup
                             completionHandler: ^(NSData *data,
                                                  NSURLResponse *response,
                                                  BOOL cachedResponse,
                                                  NSError *error) {
                                 
                                 if (error) {
                                     NSLog(@"Error: %@", error);
                                 }
                                 
                                 if (response.cou_success) {
                                     NSLog(@"Downloaded image!");
                                     UIImage *image = [UIImage imageWithData:data];
                                     dispatch_async(dispatch_get_main_queue(), ^{
                                         self.imageView.image = image;
                                     });
                                 }
                                 else {
                                     NSLog(@"Error: %li", response.cou_statusCode);
                                 }
                             }];
    [task resume];
}

@end