NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://..."]];

NSURLSessionConfiguration *configuration = nil;

NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];

NSURLSessionDownloadTask *task;

task = [session downloadTaskWithRequest:request

                      completionHandler:^(NSURL *location, NSURLResponse *response, NSError *error) {

                          dispatch_async(dispatch_get_main_queue(), ^{/* do UI thing */});

                          // or [self performSelectorOnMainThread:@selector(doUIthings) withObject:nil waitUntilDone:NO];

                      }];

[task resume];