A couple of thoughts:
First, instantiate your session with a delegate, because background sessions must have a delegate:
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:kSessionIdentifier];
self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
Second, instantiate your NSURLSessionUploadTask without a completion handler, because tasks added to a background session cannot use completion blocks. Also note, I'm using a file URL rather than a NSData:
NSURLSessionTask *task = [self.session uploadTaskWithRequest:request fromFile:fileURL];
[task resume];
Third, implement the relevant delegate methods. At a minimum, that might look like:
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data {
NSMutableData *responseData = self.responsesData[@(dataTask.taskIdentifier)];
if (!responseData) {
responseData = [NSMutableData dataWithData:data];
self.responsesData[@(dataTask.taskIdentifier)] = responseData;
} else {
[responseData appendData:data];
}
}
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
if (error) {
NSLog(@"%@ failed: %@", task.originalRequest.URL, error);
}
NSMutableData *responseData = self.responsesData[@(task.taskIdentifier)];
if (responseData) {
// my response is JSON; I don't know what yours is, though this handles both
NSDictionary *response = [NSJSONSerialization JSONObjectWithData:responseData options:0 error:nil];
if (response) {
NSLog(@"response = %@", response);
} else {
NSLog(@"responseData = %@", [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding]);
}
[self.responsesData removeObjectForKey:@(task.taskIdentifier)];
} else {
NSLog(@"responseData is nil");
}
}
Note, the above is taking advantage of a previously instantiated NSMutableDictionary called responsesData (because, much to my chagrin, these "task" delegate methods are done at the "session" level).
Finally, you want to make sure to define a property to store the completionHandler provided by handleEventsForBackgroundURLSession:
@property (nonatomic, copy) void (^backgroundSessionCompletionHandler)(void);
And obviously, have your app delegate respond to handleEventsForBackgroundURLSession, saving the completionHandler, which will be used below in the URLSessionDidFinishEventsForBackgroundURLSession method.
- (void)application:(UIApplication *)application handleEventsForBackgroundURLSession:(NSString *)identifier completionHandler:(void (^)())completionHandler {
// This instantiates the `NSURLSession` and saves the completionHandler.
// I happen to be doing this in my session manager, but you can do this any
// way you want.
[SessionManager sharedManager].backgroundSessionCompletionHandler = completionHandler;
}
And then make sure your NSURLSessionDelegate calls this handler on the main thread when the background session is done:
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session {
if (self.backgroundSessionCompletionHandler) {
dispatch_async(dispatch_get_main_queue(), ^{
self.backgroundSessionCompletionHandler();
self.backgroundSessionCompletionHandler = nil;
});
}
}
This is only called if some of the uploads finished in the background.
There are a few moving parts, as you can see, but that's basically what's entailed.
NSURLConnectionorAFNetworking– Buff