Variables In PreferenceActivity

Question

In my android application i want to make a feedback dialog that will show the second time the application is started. How can i do this ? Can i do it by variables in a PreferenceActivity. If the a variable in the preference activity is edit by feks ++; will this be the result of the variable next time the app is started ?

Edit: I dont get any of the suggested answers to work, can i create a text file on the ext or internal store the first time the app is started and check if the file exists ?