Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Another option would be:</p> <pre class="lang-c prettyprint-override"><code>NSOperationSubclass *operation = [[NSOperationSubclass alloc] init]; __weak NSOperationSubclass *weakOperation = operation; [operation setCompletionBlock:^{ NSOperationSubclass *strongOperation = weakOperation; dispatch_async(dispatch_get_main_queue(), ^{ assert(strongOperation != nil); ... }); }]; [operationQueue addOperation:operation]; </code></pre> <p>I assume you also add operation object to an NSOperationQueue. In that case, the queue is retaining an operation. It is probably also retaining it during execution of the completion block (although I haven't found official confirmation about the completion block).</p> <p>But inside you completion block another block is created. That block will be run at some point in time later, possibly after NSOperations's completion block is run to an end. When this happens, <code>operation</code> will be released by the queue and <code>weakOperation</code> will be <code>nil</code>. But if we create another strong reference to the same object from operation's completion block, we'll make sure <code>operation</code> will exist when the second block is run, and avoid retain cycle because we don't capture <code>operation</code> variable by the block.</p> <p>Apple provides this example in <a href="http://developer.apple.com/library/mac/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html" rel="noreferrer">Transitioning to ARC Release Notes</a> see the last code snippet in <em>Use Lifetime Qualifiers to Avoid Strong Reference Cycles</em> section.</p>
    singulars
    1. This table or related slice is empty.
    1. POReferencing an NSOperation object in its own completion block with ARC
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USeofster
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO+1 This is the correct answer. The `NSOperation` retains the completion block, so it is safe to use a weak reference to it in the completion block, because it's guaranteed to be still alive. However, the OP's problem is that they are using it in the second block, which is executed later, and the weak reference is not guaranteed to be alive there. The correct solution is to have the second block have a strong reference to the `NSOperation`
      singulars
      1. PO
      1. USuser102008
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload