Android how to track user's action
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I've got a question more about a strategy to use in order to implement the following requirement.

I need to develop a functionality where a user can perform some actions in the application like posting photos, commenting on photos etc. Every of this actions should leave a log somewhere and after entering one of the screens in my app, all the logs should be visible chronologically (the latest first). I've used a TreeSet sorted by item date and it works pretty fine. The problem is to keep this data persistently so that there's a never ending history of logs. I'm reluctant to migrate my code to SQLite unless it's necessary.. I like quite a lot my TreeSet structure thanks to its methods I managed to keep the logic simple. The problem starts when I'm to save this object across different launches of my app....
Has any one any idea how to solve it? Maybe TreeSet is a wrong decision though?