By now all Mac App Store developers know that all apps must have the new OSX Lion Sandboxing enabled going forward. For existing apps, we must enable it in XCode 4.2 and set in place the data migration plist.
So my existing Mac App Store app has a build target of OSX 10.6.8 Snow Leopard. Not only that, but it does access the webcam and also synchronizes stuff to iCal via CalendarStore API and AppleScript. I'm expecting most of my app to break when I enable the Sandbox, but when I get that working in the Sandbox I'm wondering if a Sandboxed app can run in Snow Leopard.
Does anybody have experience in migrating to the Mac App Sandbox? I would like to know if enabling this would break Snow Leopard compatibility, and what I am up against given the entitlements my app will require.
Snow Leopard is an awesome OS and I'd like to support it as long as reasonably possible, for those users who have a Mac not quite new enough to run Lion.
After enabling entitlements and sandbox while still keeping the build target as 10.6, I was able to get my app up to speed so it operates within the sandbox in Lion. E.g. file access, calendar access, webcam access.
Once I had that taken care of, I built a .pkg file and installed it on my old Mac Mini running Snow Leopard. It seems to run in Snow Leopard just as it did before. Unlike Lion, it won't migrate your config and plist-defined folders as it seems the sandbox stuff that is compiled in is completely ignored when run under Snow Leopard (which makes sense since the Lion kernel is probably doing all the work).
So there you have it, the short answer for backwards compatibility is "Yes". Although who is to say Apple won't restrict 10.6 targeted builds from being uploaded to the Mac App Store once March 1st hits? Probably not, but it will happen eventually. I'm not trying to start a rumor or anything, it's just a thought.
Anyways, I hope Apple continues to let us support Snow Leopard users, as I imagine they are still the majority of the Mac users out there. Take this article with a grain of salt, but still...
http://www.theverge.com/2011/11/11/2554009/mac-os-x-lion-adoption-slowing
来源：https://stackoverflow.com/questions/8677216/app-sandbox-icloud-and-snow-leopard-backwards-compatibility