When using GCD, we want to wait until two async blocks are executed and done before moving on to the next steps of execution. What is the best way to do that? We tried the following, but it doesn’t seem to work: dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ { // block1 }); dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ { // block2 … Read more
I have a working app and I’m working on converting it to ARC in Xcode 4.2. One of the pre-check warnings involves capturing self strongly in a block leading to a retain cycle. I’ve made a simple code sample to illustrate the issue. I believe I understand what this means but I’m not sure the … Read more
Block syntax in Objective C (and indeed C, I presume) is notoriously incongruous. Passing blocks as arguments looks different than declaring blocks as ivars, which looks different than typedefing blocks. Is there a comprehensive list of block-declaration syntax that I could keep on hand for quick reference? 7 Answers 7
Is it possible to have blocks as properties using the standard property syntax? Are there any changes for ARC? 8 Answers 8
I’m getting an error Variable is not assignable (missing __block type specifier) on the line aPerson = participant;. How can I make sure the block can access the aPerson variable and the aPerson variable can be returned? Person *aPerson = nil; [participants enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) { Person *participant = (Person*)obj; if ([participant.gender … Read more
What exactly does the __block keyword in Objective-C mean? I know it allows you to modify variables within blocks, but I’d like to know… What exactly does it tell the compiler? Does it do anything else? If that’s all it does then why is it needed in the first place? Is it in the docs … Read more
Is there a way to call a block with a primitive parameter after a delay, like using performSelector:withObject:afterDelay: but with an argument like int/double/float? 20 s 20 I think you’re looking for dispatch_after(). It requires your block to accept no parameters, but you can just let the block capture those variables from your local scope … Read more
