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I’m not a fan of mobile games that allow you to bribe your way to victory, even though they are as reliable a business model as advertising is for websites. I wanted to learn Android programming and making a parody of this type of game seemed like a decent scope for a “My First Android” kind of project. Thus, I set out to create a game of tic-tac-toe where the AI plays perfectly (and is therefore unbeatable) unless you pay 99 cents in which case it plays randomly and can be beaten 99.4792%1 of the time.

Design overview

I needed four classes for this a TicTacToeBoard which stored a game state, calculated the computer’s moves, and provided a variety of library functions, a MainActivity which showed the actual tic tac toe board and had a drop down menu, an AboutPage which was an activity that showed some info about me, and a ScorePage which was an activity that displayed the user’s cumulative wins, losses, and draws.

When the app needed to save MainActivity’s state it did so by writing the board out as 10 strings, 9 to represent the text in each space and one to say which person had just moved, we then had two strings to say the computer and player’s chars,2 and a flag to track whether we were in easy mode or not.3

In our long-term storage, we currently have a flag to keep track of whether we have ever played before and integers for the user’s number of wins, losses, and draws.4

Challenges encountered

Making my first Android app was a quick journey, but one beset by challenges. Most of them were due to me not yet knowing how to do Android programming, but one or two may have been actually difficult.

There were three bugs that troubled me long enough for me to have made a ticket for them. First, when I was trying to set the MainActivity as an onClickListener for the nine buttons it would crash. The fix for this was to call setContentView before trying to register for those events. Second, rotating MainActivity’s screen would make the tic-tac-toe board disappear. I fixed this at first by fixing the orientation of MainActivity. I then fixed it properly by making TicTacToeBoard implement Parcelable and overriding onSaveInstanceState and onRestoreInstanceState. This solution had a bug where pressing the Verizon button on my phone would cause it to crash, this was just a dumb mistake in my parceling code. Third, it wouldn’t preserve anything when I switched screens or logged in or out. This was solved by setting android:launchMode="singleTop" in the manifest.5

Something I struggled with generally, but that isn’t technically a bug was in app billing. There’s a good tutorial here which was helpful at the end after I tried everything else. Testing my in-app billing was also kinda hard, since Google doesn’t allow developers to buy things from themselves.6 What you’re supposed to do is have a spare device with a test account installed on it. Since I currently only own one phone, I just reached out to a friend, Kunal, who does mobile programming and got them to be a beta tester for me. He also helped by telling me the “best” way to fix some of the bugs I encountered in the previous paragraph.

Future work

There were a lot of possible enhancements that I would or should put in a more commercial app, but which I decided were out-of-scope for this. I should have used a namespace for my product ID, I went with "sku_easy_mode" because I saw an example somewhere using SKUs. They may have meant it in a different way. I could have used a licensing scheme to validate that the app was installed from the official channel, but I wasn’t convinced this would benefit me and I ran into time constraints before getting back around to it. I could have made some popups to talk with the user, but I felt that toasts were sufficient for my purposes. I could have had an Unbeatable TicTacToe logo show up, which would change into a Beatable TicTacToe logo when easy mode was enabled.

I might want to take the current app and just make it look prettier. The about page could have separate text boxes for the links with thumbnail images next to them, the score page could have big text boxes for the actual score and then a message at the bottom making a snarky comment about the user either being bad at the game (if they lose a lot), being just as smart as a computer (if they mostly draw), or wasting money on tic-tac-toe (if they win a couple times with easy mode), the main activity could have stylized text boxes to make the tic-tac-toe board prettier and it could resize to fill the screen. I also have an idea for a much more serious game than tic-tac-toe, but as a firm believer that ideas are worthless and execution is everything I’ll wait to announce it until I actually have an alpha.7

One thing I really want on Android is a music player that preserves your spot when you pause and come back later. The default music player on my Samsung doesn’t do that, but if you download a long audio file, say a podcast, as an mp3 and try to listen to it in pieces it’s critical that you can find the spot you left off easily. I’m going to look around for pre-existing work before I do this though.

Lessons Learned

I needed to get a Google Play Developer account and a Google Pay Merchant account in order to publish this app. I’m on the very edge of getting my own LLC and officially becoming a business, but I’ll most likely delay that until I have separate business income.

I also learned to use a more modern IDE, most of my programming is done in gvim, but all of the Android tutorials I read wanted me to use Android Studio and my desire to be a rebel just wasn’t strong enough. This worked well for me, autocompletion was a nice feature and so was being able to run an app by clicking a button. Looking back, this project is a lot like life. I could have done it a lot better, but I stand by the work I did.


  1. This is an exact number. I know this because Jane Street had a puzzle to find this number in May, but this can also be calculated by hand.

  2. Some of that data is redundant. For example, if we know the player’s symbol, we can find the computer’s symbol, if we have the game board we can determine if X just moved by seeing if there are more X’s than O’s. The minimum number of bits needed to store the TicTacToeBoard is 16. One bit tracks whether the player is X or O, we then need “log2(3)” bits to store whether each of the nine spots is an X, O, or free. “log2(3) * 9+1 = 15.2646625065” bits, which rounds up to 16. My choice to store redundant data is solely because I believe that programmer time and the risk of bugs that naturally comes with more complex code is more expensive than disk space.

  3. Tracking whether the game is currently in “easy mode” was originally done using “SharedPreferences”, but was refactored to be stored in a “Bundle” by “onSaveInstanceState” in version 1.3.2. I then used my Orwellian editor powers to change this blog post accordingly.

  4. Of course, this means that if someone plays more than two billion times. Parts of their score may start to wrap around to negative two billion. If you plan on playing this game that much, please let me know and I will fix this issue.

  5. I essentially had this.

  6. As explained in don smolen’s answer here.

  7. Somewhat relevant reading is here.

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