Question

I ran into this problem while trying to fix a memory leak with the facebook-ios-sdk. How do i handle this situation when passing objects from no arc compiled classe to arc enabled classe?

This is the code inside the non arc compiled Facebook library: (i removed the unnecessary stuff which is not related to the problem) as you can see, result object is not autoreleased or released.

- (void)handleResponseData:(NSData *)data {        
    NSError* error = nil;
    id result = [self parseJsonResponse:data error:&error];
    self.error = error;

    // Call the defined delegate wich is my AppDelegate didLoad method wich is arc enabled
    [_delegate request:self didLoad:result];
}

- (id)parseJsonResponse:(NSData *)data error:(NSError **)error {
    SBJSON *jsonParser = [[SBJSON alloc] init];

    //gets the object wich leaks or gets overreleased
    id result = [jsonParser objectWithString:responseString];
    [jsonParser release];

    return result;
}

Now if i try to add autorelease to the result object, i am facing a NSZombie when my arc code in my AppDelegate try’s to release the object. However if i leave the code like this i’m facing memory leaks whit the result object which gets not released.

am i missing something basic? i can’t get my head around this?

Thanx for any advice! Chris

Answer 1

The result returned from -parseJsonResponse:... is autoreleased already (see note at bottom).

Since the name of the -parseJson method doesn’t begin with new, alloc, copy or mutableCopy, the compiler assumes that it returns an object with a +0 reference count, meaning it needs to be retained by the calling code if it is to be kept around, and doesn’t need to be released if it’s not being kept around. That’s a long winded way of saying that it should neither leak nor cause a crash in your ARC code as written in your question.

Passing objects between ARC code and manual reference counting code doesn’t require any special handling. You just need to make sure that methods’ names match their memory management semantics in the non-ARC code. It certainly seems like you’ve done that in this case, although as you say, you didn’t post your complete code.

Note: Presumably, objectWithString: returns an autoreleased object. If it doesn’t it, it should (because it doesn’t start with alloc, new, copy, mutableCopy).