#objective-c-blocks

Fixed How do I avoid capturing self in blocks when implementing an API? #dev #it #asnwer

How do I avoid capturing self in blocks when implementing an API?

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 selfstrongly 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 “correct” or recommended way to implement…

Fixed What does the "__block" keyword mean? #dev #it #asnwer

What does the "__block" keyword mean?

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 anywhere? (I can’t find it).

Thanks!

Answer: What does the "__block" keyword…

Fixed Assign a variable inside a Block to a variable outside a Block #dev #it #asnwer

Assign a variable inside a Block to a variable outside a Block

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…

Fixed Block Declaration Syntax List #dev #it #asnwer

Block Declaration Syntax List

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?

Answer: Block Declaration Syntax List

The Xcode 4 snippet…

How to: Declare a block method parameter without using a typedef

Declare a block method parameter without using a typedef

Is it possible to specify a method block parameter in Objective-C without using a typedef? It must be, like function pointers, but I can’t hit on the winning syntax without using an intermediate typedef:

typedef BOOL (^PredicateBlock_t)(int); - (void) myMethodTakingPredicate:(PredicateBlock_t)predicate

only the above compiles, all these…

Fixed How do you trigger a block after a delay, like -performSelector:withObject:afterDelay:? #dev #it #asnwer

How do you trigger a block after a delay, like -performSelector:withObject:afterDelay:?

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?

Answer: How do you trigger a block after a delay, like -performSelector:withObject:afterDelay:?

How about something like this:

dispatch_async(…

How to: Retain cycle on `self` with blocks

Retain cycle on `self` with blocks

I’m afraid this question is pretty basic, but I think it’s relevant to a lot of Objective-C programmers who are getting into blocks.

What I’ve heard is that since blocks capture local variables referenced within them as const copies, using self within a block can result in a retain cycle, should that block be copied. So, we are supposed to use __blockto force…

How to: How do I avoid capturing self in blocks when implementing an API?

How do I avoid capturing self in blocks when implementing an API?

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 selfstrongly 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 “correct” or recommended way to implement…