I have created a app and i want to make it as payed app with trial download. But i want to limit the user to use the app for 20 times.

Everything is ok, and the app is working for 20times and at the 21st time it shows trial expired and asking to buy the app.

BTW i am using teleriks RAD control "RadTrialApplicationReminder" for checking the app usage status.

But the problem is when the user uninstall the app on the device and reinstall it again he can use the app again for 20times

How can i make the app for using only 20 times for trial?

Else any other easy way to overcome this/

Any help?