From the docs about __block __block variables live in storage that is shared between the lexical scope of the variable and all blocks and block copies declared or created within the variable’s lexical scope. Thus, the storage will survive the destruction of the stack frame if any copies of the blocks declared within the frame … Read more
You can use the __block storage type qualifier for such a case. __block variables are not automatically retained by the block. So you need to retain the object by yourself: __block UIViewController *viewController = [myViewController retain]; dispatch_async(backgroundQueue, ^{ // Do long-running work here. dispatch_async(dispatch_get_main_queue(), ^{ [viewController updateUIWithResults:results]; [viewController release]; // Ensure it’s released on main … Read more
This is not a retain cycle. A retain cycle would be self -> block -> self In this case we have animation framework -> block block -> self where the first retain is only temporary – the block gets released when the animation ends. Even if a retain cycle happens, it will be only temporary … Read more
I’d like to explain this a bit more, with a more complete answer. First let’s consider this code: #import <Foundation/Foundation.h> int main(int argc, char *argv[]) { void (^block)() = nil; block(); } If you run this then you’ll see a crash on the block() line that looks something like this (when run on a 32-bit … Read more
It’s actually fairly straightforward and described in Clang’s Block Implementation Spec, in the “Imported Variables” section. When the compiler encounters a Block like: ^{ if( numBalloons > numClowns) abort(); } it creates a literal structure that includes — among other things — two elements that are important here. There’s a function pointer to the executable … Read more
__block is a storage qualifier. It specifies that the variable should directly be captured by the block as opposed to copying it. This is useful in case you need to modify the original variable, as in the following example __block NSString *aString = @”Hey!”; void(^aBlock)() = ^{ aString = @”Hello!” }; // without __block you … Read more
Can do, kinda sorta. But first, let’s disambiguate. -[NSObject isKindOfClass:] can tell you it’s a block, and that’s about it. E.g. I believe this line of code — ostensibly & unfortunately A BAD IDEA — will return YES for blocks on present Lion & iOS 5.x: [myBlock isKindOfClass:NSClassFromString(@”NSBlock”)] That won’t help you distinguish the block’s … Read more
Assign whatever identifier you want using dispatch_queue_set_specific(). You can then check your identifier using dispatch_get_specific(). Remember that dispatch_get_specific() is nice because it’ll start at the current queue, and then walk up the target queues if the key isn’t set on the current one. This usually doesn’t matter, but can be useful in some cases.
I always use this when I want to write a block: http://fuckingblocksyntax.com EDIT If you are writing Swift then use this: http://fuckingswiftblocksyntax.com If the above links are not opening because of the obscene language, use this one. http://goshdarnblocksyntax.com/
Doh. Dear future googlers: of course operation is nil when copied by the block, but it doesn’t have to be copied. It can be qualified with __block like so: //THIS MIGHT LEAK! See the update below. __block NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{ while( ! [operation isCancelled]){ //do something… } }]; UPDATE: Upon further meditation, it … Read more