How to migrate from a paid android application to an application paid for with in-app billing?

Question

I currently have two versions of my app in the Android market, a paid one and a free one. But I want to integrate in-app billing into my free application, and charge customers on a subscription base, for a lower price than the current price of the paid app.

But how should I handle this for existing customers? It seems unfair to let them pay again for use of the paid functionality, while they were the early adopters of my application. Ideally I implement something that will give the existing users access to the unlocked functionality in my free application.

Any ideas of how to accomplish this? An outline of a good approach to take is enough, I don't mind to do some research on how to actually implement such an approach.

Answer 1

Release a separate free version of your app; use the paid version as if it were a license key to the free version.

PackageManager manager = getPackageManager();
if (manager.checkSignatures("old.package.name", "new.package.name")
    == PackageManager.SIGNATURE_MATCH) {
    //full version
}