Change a Paid Android app to a Free app with in-app purchasing

It's been a year, so the OP probably doesn't need this, but in case anyone else happens upon this one...

You could approach this a couple of ways. Obviously there is some business logic on your new in-app purchasing app to track who has/hasn't paid. So the two ways I see you being able to go about this is as follows:

Idea 1:

You could do a preliminary update to your paid app that stores a SharedPreference or some other persistence in the app (you could store the versionCode, so you know what you're upgrading from and have business logic around that). Then update to the free version, and have the free version check your shared preference and do the right thing on an update from a "paid" versionCode.

Idea 2:

You could keep both apps separate (have a paid version and a free with in-app purchases) and push an update to the paid version to have a BroadcastReceiver that doesn't really do anything other than listen to specific intents and have your in-app purchase check to see if something will receiver your custom intent. If your old paid-version exists, then they paid for it, if not they didn't. (If they paid for the paid version then uninstalled you'll have problems obviously...)

Idea 3:

You could keep both apps separate (have a paid version and a free with in-app purchases), and push an update to the paid version that just posts an Intent to open the in-app purchase app (if it's installed) with some special arguments, to let you know they opened it via a paid app and do the right thing to set them up as having paid for it in-app. That opens yourself up to some detection problems though... (Solvable but kind of clunky)