Having found Conway’s Game of Life to be a useful kata in C#, I thought I’d use it to explore some other technology. I’ve had an HTC Desire Android smartphone for a little while, so thought I’d see how hard it was to port something over.
I was hit by a number of gotchas while writing it – mostly down to using the API for the first time, and by not using Eclipse, instead using notepad++ and jdb to code and debug. jdb gave me a little trouble, but soon figured it out (on stackoverflow and here), realising that I had to make a socket connection to the emulator, and not the shared memory connection I seemed to be defaulting to.
I worked up a very simple app by just porting the core Life code I create in kata to Java, and then writing a minimal presenter over the top. The presenter comprises an Activity and an View; the Activity was just responsible for spinning up the backend engine – the View. The View is responsible both for keeping the evolution of the cells going, and displaying the current state. Dirty, but it worked.
Converting the app to a live wallpaper sees the Activity transformed into a WallpaperService, which means we need to override the method onCreateEngine – in the case of a live wallpaper a specific Engine class actually drives the underlying model, and presents you with a SurfaceHolder on which to render the wallpaper.
As a result, LifeEngine was reworked to inherit from Engine and render using a SurfaceHolder rather than a Canvas. The only real wrinkle there is that the Surface doesn’t get wiped between renders, so you need to wipe it yourself.
I wanted to pop up a dialog or other window when the user tapped the screen – that turned out to be not as straightforward as I’d assumed from a wallpaper. Handling the tap is easy enough, but bringing up a dialog less so.
Currently you can download the wallpaper here on the market, and the project should be up soon.
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