Android paid applications

There are a few apps on the market that are set开发者_如何学运维 up to have a free main component(which is a trial limited to 7 days lets say) then "recharge" apps that will add a certain amount of subscription time to an account for the user that allows them to keep using the main app. These "recharge" apps are available in the market as well. What I would like to know is how to make it so that once the user has paid for one of these "recharge" apps and used it to add time to their subscription, they are unable to uninstall it and re-download it(for free since they paid for it once). Basically how do I set my application up so that you only get 1 successful download of the app from the market per payment. Once the time has been added to the users account I would like the market to behave as though the "recharge" app has never been purchased.

What I would like to know is how to make it so that once the user has paid for one of these "recharge" apps and used it to add time to their subscription, they are unable to uninstall it and re-download it(for free since they paid for it once).

You cannot prevent them from uninstalling and re-downloading it. At most, you might work out your own mechanism to prevent the app from applying a new "recharge".

Once the time has been added to the users account I would like the market to behave as though the "recharge" app has never been purchased.

This is not possible. In fact, it works in the reverse -- the user will forevermore be able to download it, on as many devices as they want, so long as they are using the same Google account for each device. Purchases of apps are for the lifetime of the Android Market, not for a developer-selected lifetime.

Check out the new in app billing functionality, you may be able to leverage some of it's functionality to sell additional functionality/subscription time.

Setup a server and once the user downloads the app, on the first start the app shall connect to your webserver and send the IMEI oder device serial number to the server and the server will send a code which enables all the features.

Since the date of the first activation is stored on your database on your server, the user won't be able to change it until he puts in a new SIM Card (hence changing his IMEI number) even if he redownloads the application several time, the IMEI basically never change unless you change the SIM.