Delegate.m

- (void) downloadImage {
    NSString *imageUrl = @"http://images.apple.com/v/watch/c/images/nav_sport_large.jpg";
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];

    NSURLSession *session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:nil ];

    NSURLSessionTask *downloadTask = [session downloadTaskWithURL:[NSURL URLWithString:imageUrl]];

    [downloadTask resume];
}

-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
    // use code above from completion handler
}

//For progress indication
-(void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    NSLog(@"%f / %f", (double)totalBytesWritten,
          (double)totalBytesExpectedToWrite);
}