This was one of my 1st projects in Android. Not the best but a good one to begin with. After a while when I was more confortable with Android I have modified this code and upload the app on playstore - https://play.google.com/store/apps/details?id=com.osfg.tictactoe
Thought the final code is not merged back here. This is should be a good starting point for beginners Android project.