Here’s another good tutorial at MobileOrchard — my, they are on a run lately, aren’t they? — Lite To Paid iPhone Application Data Migrations With Custom URL Handlers.
Apple enforces a number of restrictions on applications in the App Store. Among the most painful is the lack of feature-limited trials. Applications are either completely free, or the customer must pay up front, sight unseen. The proliferation of “Lite” applications is a direct result of this shortcoming…
When building a game or other stateless application the approach makes complete sense. However, utility applications often maintain information entered by the device owner. Application authors are faced with a dilemma because the iPhone’s security sandbox prevents one application from reading another application’s files. Thus, when customers upgrade from the Lite application they are penalized by having to re-enter all data!
This is rather apropos, as we’ve been already planning something along these lines for migrating data from paid for 2.0 applications to new StoreKit-using 3.o applications, which is more or less the same basic problem as the Lite-to-Pro style migration they have in mind.
The tutorial goes on into exhaustive detail, but the basic idea is to use URL handlers for IPC between your application versions as we’ve mentioned earlier. We do have one additional tip to add though; they focus on using solely the URL itself to transfer data, which there’s a good chance to be problems with using for data in the dozens of megabytes like we need to do. Luckily, we have another earlier post of ours to point you at what looks like a fruitful avenue of inquiry; figure out where UIImagePickerController writes its photographs, which it seems is and is likely to continue to be necessarily a shared access folder, and stick your large temporary data in there. We’ll let you know how that works out once we’ve tried it!
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The source code is under the GPL, but the data is still strictly copyright Id Software with no license given to distribute outside this code release package or to use for any commercial purpose. You are certainly free to replace all the data and make commercial applications, as long as the code is made available under the GPL.