External app to act as a full version key

I have noticed some apps use a second app just to act as their key for full version - this way there is no need to have two versions of the app 开发者_如何学编程just the free one and a full version unlocker.

How would I go about implementing this?

Thanks, Jason

All you need is here How can I use the paid version of my app as a "key" to the free version?

In Android intents are self contained, so the free app could have say 3 intents. And when the user runs the free app, he interacts with the 3 intents. The paid app has say 3 intents and also call the 3 intents of the free app, thus providing the paid + free functionality in the app. I haven't implemented this but I think this would be the way to do this. Others can correct me if I am wrong.

I personally would just overwrite the free app with the paid app and keep this simpler to manage. In terms of maintenance this is one less app to track and manage features.