NSOperationQueue，weakSelf和block的问题

Question

我有以下代码：

 [[AHPinterestAPIClient sharedClient] getPath:requestURLPath parameters:nil 
             success:^(AFHTTPRequestOperation *operation, id response) {


                 [weakSelf.backgroundQueue_ addOperationWithBlock:^{
                     [self doSomeHeavyComputation];                    


                     [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                           [weakSelf.collectionView_ setContentOffset:CGPointMake(0, 0)];
                     [weakSelf.collectionView_ reloadData];
                     [weakSelf.progressHUD_ hide:YES];
                     [[NSNotificationCenter defaultCenter] performSelector:@selector(postNotificationName:object:) withObject:@"UIScrollViewDidStopScrolling" afterDelay:0.3];
                     [weakSelf.progressHUD_ hide:YES];


                      }];

                  }];

             }
             failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                [weakSelf.progressHUD_ hide:YES];
                [weakSelf.collectionView_.pullToRefreshView stopAnimating];
                 NSLog(@"Error fetching user data!");
                 NSLog(@"%@", error);
             }];

出于某种原因，这在iOS 5中运行得很好，但不是iOS 6（崩溃）。现在我不打算询问iOS 6，因为它仍然在NDA下。我想知道的是，上面的代码是否错误？如果是，我该如何解决它。

如果我把代码放在mainQueue之外的块中，那就没关系了。 我在这里要做的是仅在[self doSomeHeavyComputation]完成后才执行NSOperationQueue mainQueue。所以这是一个依赖，我该如何添加这个依赖？

更新

如果它有帮助，这是崩溃日志：

Answer 1

建议在块中“展开”弱引用，所以请尝试：

__weak id weakSelf = self;
[client getPath:path parameters:nil success:^(id op, id response) {
    id strongSelf = weakSelf;
    if (strongSelf == nil) return;

    __weak id internalWeakSelf = strongSelf;
    [strongSelf.backgroundQueue_ addOperationWithBlock:^{
        id internalStrongSelf = internalWeakSelf;
        if (internalStrongSelf == nil) return;

        [internalStrongSelf doSomeHeavyComputation];                    

        __weak id internalInternalWeakSelf = internalStrongSelf;
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            id internalInternalStrongSelf = internalInternalWeakSelf;
            if (internalInternalStrongSelf == nil) return;

            [internalInternalStrongSelf reloadCollectionView];
        }];
    }];
}
failure:^(id op, NSError *error) {
    id strongSelf = weakSelf;
    if (strongSelf == nil) return;

    [strongSelf stopProgress];
    NSLog(@"Error fetching user data: %@", error);
}];