Passing delegate through another object with ARC

Question

I've got 2 classes, MPRequest and MPModel . The MPModel class has a method to lookup something from the core data store, and if not found, creates an MPRequest to retrieve it via a standard HTTP request (The method in MPModel is static and not and instance method).

What I want is to be able to get a progress of the current HTTP request. I know how to do this, but I'm getting a little stuck on how to inform the view controller. I tried creating a protocol, defining a delegate property in the MPRequest class, altering the method in MPModel to accept this delegate, and in turn passing it to the MPRequest when it is created.

This is fine, however ARC is then releasing this delegate whilst the request is running and thus doesn't do what I want. I'm trying to avoid making my delegate object a strong reference in case it throws up any reference cycles but I don't know any other way of doing this.

To start the request, from my view controller I'm running

[MPModel findAllWithBlock:^(NSFetchedResultsController *controller, NSError *error) {
    ....
} sortedBy:@"name" ascending:YES delegate:self]

Inside the findAllWithBlock method, I have

MPRequest *objRequest = [MPRequest requestWithURL:url];
  objRequest.delegate = delegate;

[objRequest setRequestMethod:@"GET"];
[MPUser signRequest:objRequest];

[objRequest submit:^(MPResponse *resp, NSError *err) {
    ...
}

And in the MPRequest class I have the following property defined :

@property (nonatomic, weak) NSObject<MPRequestDelegate> *delegate;

Any ideas or suggestions?

As requested, here is some more code on how things are being called :

In the view controller :

[MPPlace findAllWithBlock:^(NSFetchedResultsController *controller, NSError *error) {
        _placesController = controller;
        [_listView reloadData];
        [self addAnnotationsToMap];
        [_loadingView stopAnimating];

        if (_placesController.fetchedObjects.count > 0) {
            // We've got our places, but if they're local copies
            // only, new ones may have been added so just update
            // our copy
            MPSyncEngine *engine = [[MPSyncEngine alloc] initWithClass:[MPPlace class]];
                 engine.delegate = self;
            [engine isReadyToSync:YES];
            [[MPSyncManager sharedSyncManager] registerSyncEngine:engine];
            [[MPSyncManager sharedSyncManager] sync];
        }
    } sortedBy:@"name" ascending:YES delegate:self];

Here, self is never going to be released for obvious reasons, so I don't see how this is the problem.

Above, MPPlace is a subclass of MPModel , but the implementation of the findAllWithBlock:sortedBy:ascending:delegate: is entirely in MPModel

The method within MPModel looks like this

NSManagedObjectContext *context = [[MPCoreDataManager sharedInstance] managedObjectContext];
[context performBlockAndWait:^{
    __block NSError *error;
    NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:NSStringFromClass([self class])];
    [request setSortDescriptors:@[[[NSSortDescriptor alloc] initWithKey:key ascending:asc]]];

    NSFetchedResultsController *controller = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                                 managedObjectContext:context
                                                                                   sectionNameKeyPath:nil
                                                                                            cacheName:nil];

    [controller performFetch:&error];

    if (!controller.fetchedObjects || controller.fetchedObjects.count == 0) {
        // Nothing found or an error, query the server instead
                NSString *url = [NSString stringWithFormat:@"%@%@", kMP_BASE_API_URL, [self baseURL]];
        MPRequest *objRequest = [MPRequest requestWithURL:url];
          objRequest.delegate = delegate;

        [objRequest setRequestMethod:@"GET"];
        [MPUser signRequest:objRequest];

        [objRequest submit:^(MPResponse *resp, NSError *err) {
            if (err) {
                block(nil, err);
            } else {
                NSArray *objects = [self createListWithResponse:resp];
                         objects = [MPModel saveAllLocally:objects forEntityName:NSStringFromClass([self class])];
                [controller performFetch:&error];
                block(controller, nil);
            }
        }];
    } else {
        // Great, we found something :)
        block (controller, nil);
    }
}];

The delegate is simply being passed on to the MPRequest object being created. My initial concern was that the MPRequest object being created was being released by ARC (which I guess it probably is) but it didn't fix anything when I changed it. I can't make it an iVar as the method is static.

The submit method of the request looks like this :

_completionBlock = block;
   _responseData = [[NSMutableData alloc] init];

[self prepareRequest];

[self prepareRequestHeaders];
_connection = [[NSURLConnection alloc] initWithRequest:_urlRequest
                                              delegate:self];

And when the app starts downloading data, it calls :

[_responseData appendData:data];
[_delegate requestDidReceive:(float)data.length ofTotal:_contentLength];

Where _contentLength is simply a long storing the expected size of the response.

Answer 1

Got it working. It was partly an issue with threading, where the core data thread was ending before my request, me looking at the output from a different request entirely, and the way ARC handles memory in blocks.

Thanks for the help guys