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Before ARC I had the following code that retains the delegate while an async operation is in progress:
- (void)startAsyncWork { [_delegate retain]; // calls executeAsyncWork asynchronously } - (void)executeAsyncWork { // when finished, calls stopAsyncWork } - (void)stopAsyncWork { [_delegate release]; } What is the equivalent to this pattern with ARC?
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The system that Objective-C uses is called retain/release. The basic premise behind the system is that if you want to hold on to a reference to another object, you need to issue a retain on that object. When you no longer have a use for it, you release it. Similar to Java, each object has a retain count.
You send an object a retain message when you want to prevent it from being deallocated until you have finished using it. An object is deallocated automatically when its reference count reaches 0 . retain messages increment the reference count, and release messages decrement it.
Automatic Reference Counting (ARC) is a memory management option for Objective-C provided by the Clang compiler. When compiling Objective-C code with ARC enabled, the compiler will effectively retain, release, or autorelease where appropriate to ensure the object's lifetime extends through, at least, its last use.
I have occasionally needed to manually retain and release things (sometimes just for debugging) and came up with the following macros:
#define AntiARCRetain(...) void *retainedThing = (__bridge_retained void *)__VA_ARGS__; retainedThing = retainedThing #define AntiARCRelease(...) void *retainedThing = (__bridge void *) __VA_ARGS__; id unretainedThing = (__bridge_transfer id)retainedThing; unretainedThing = nil This works by using the __bridge_retained and __bridge_transfer to cast things to and from (void *) which causes things to be retained, or to create a strong reference without calling retain.
Have fun, but be careful!
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Why not just assign your delegate object to a strong ivar for the duration of the asynchronous task?
Or have a local variable in executeAsyncWork
- (void)executeAsyncWork { id localCopy = _delegate; if (localCopy != nil) // since this method is async, the delegate might have gone { // do work on local copy } } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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