问题
I'm considering dropping 32-bit support for in favor for Automatic Reference Counting (which is only supported for 64 bit binaries).
I'd like to avoid these two scenarios with the Mac App Store:
For a user of an old 32-bit Mac:
who did purchase the previous version with 32-bit support: Will they see an update message for the app in the Mac App Store? If so, the (now 64 bit only) update would not work for him/her.
who has not purchased the app before: will they be able to purchase the app although it will not run on their system?
ARC 64 bit only: http://developer.apple.com/library/mac/#releasenotes/ObjectiveC/RN-TransitioningToARC/_index.html#//apple_ref/doc/uid/TP40011226
EDIT: I found one occasion of somebody being able to download a 64 bit only app to a 32 bit MacBook and being presented with an error message "Your purchase could not be completed". In this case it was a free app. I wonder when this message would pop up for a paid app (before or after the payment).
http://www.linethirteen.com/blog/2011/01/mac-app-store-32-bit-vs-64-bit/
回答1:
I've also found out that ARC requires 64bit processors. However, I managed to build a fat binary where the 64bit version uses ARC and the 32bit version uses the garbage collector. To do this I had to do the following:
- set up a 32bit only target that uses GC
- set up a 64bit only target that uses ARC
- add the 32bit target as a dependency to the 64bit target
- add a custom build phase with a shell script that uses
lipoto assemble a fat binary from the binaries in the two targets
Both targets use the same source, but a few #ifdef __OBJC_GC__ statements were necessary. I did have to give up synthesized ivars for backward compatibility :(
回答2:
I don't know what App Store will do (and it's probably subject to change, anyway), but if the app does get delivered to 32-bit customers, you can work around the problem in this way:
- Make your app 64-bit only.
- Make a second app that is 32-bit only and does nothing but show an alert message.
- Build all of the resources from the second app into the first (i.e., add them to both targets).
- Make the second target a dependency of the first, and use
lipoin a shell script phase in the first target to assimilate the 32-bit binary into the 64-bit binary.
You'll then have a Universal Binary (or “fat binary”) that is your real application on 64-bit machines, and the “please upgrade your Mac” application on 32-bit machines.
来源：https://stackoverflow.com/questions/7865423/mac-app-store-giving-up-32-bit-support-in-favor-for-arc-will-existing-users-of