I am making an app.Which has a free trial version and a premium version.The free version runs as premium for 7 days and after that it will prompt user to buy premium and exit.To do so I have come up with some ideas such as:
1)Identify the device uniquely and send that unique id and date to a server.And on start up check if this device’s app is more than 7 days old if so block it.And when the user uninstalls the app and installs again upon registering to the server the app will be blocked.I have read about some ways of identifying a device uniquely.But as this link suggests none of them is reliable and won’t work on every device and OS version.
2)I can write a file to sdcard indicating the app installation and check for that particular file on first run to detect re-installation.But that file can be easily deleted by the user and the app re-installed thus obtaining another trial for 7 days which is not acceptable.
Is there a way I can attain my goal?
These things can be done but, I encourage you to think again. What you’re proposing is not good for your users and not good for users usually means lower app sales.
The app has to check with your server every time it starts. So I can’t use it if I have no data connection or your server is down? Even if I paid for it?
Whatever you do, it can be defeated, especially if using date bound stuff.
I recommend that you think about adding value to the premium version, which is not in the free version, that will encourage people to buy. Or support the free one with advertising, which a lot of people will gladly pay a reasonable amount to get rid of. I recommend NOT releasing a free version which is in someway crippled but rather to make your paid version valuable to the user.