Transitioning Audio Unit code to ARC

Question

Apologies if this is too vague... this is my first post here and I'm well and truly stumped on this issue!

I've been attempting to transition an iOS Xcode project using Audio Units to ARC, but it appears to have broken the functionality of the audio unit processing class. Some symptoms... When I attempt referencing 'self' in AUProcessor.mm, the AUProcessor class is referred to as 'const*', whereas in the pre-ARC version, there was no 'const*' mentioned.

This pointer to 'self' produces the following error:

callbackStruct.inputProcRefCon = self;

[error] Assigning to 'void *' from incompatible type 'AUProcessor *const __strong'.

I can remove the error by adding (__bridge void*) ahead of self, which allows the project to compile. However, the Audio Unit processor doesn't work in the app.

I can't see anything elsewhere in the code that is significantly different from the pre-ARC version in terms of how the class is referenced.

Let me know if more context is required.

Thanks in advance!!

(BTW, thank you to all contributors to these forums... they are truly a wonderful resource for keen yet inexperienced programmers!)

Answer 1

Typically, (__bridge void*) would be the correct cast here. This means "take a pointer to this object without applying any memory management; I promise I'll hold onto it for as long as it's needed." (That last part is just implied, but if you don't, you'll crash.)

Are you certain that self continues to exist for as long as this audio unit? If nothing has a strong reference to self, then it will disappear and inputProcRefCon will become a dangling pointer.

When you say "doesn't work in the app," what do you mean? Does it crash? Does the callback not happen? When the callback happens, does it not have the right data?

Answer 2

I managed to resolve my issue by excluding the troublesome class from ARC using the compiler flag -fno-objc-arc.

Its not a very satisfying conclusion but at least my app is working again... Looks like I'm going to need to learn more about memory management!