An Android Game Development Framework - Beginning Android Games - page 193

The AndroidAudio implementation has an AssetManager and a SoundPool instance. The
AssetManager is necessary for loading sound effects from asset files into the SoundPool on a call
to AndroidAudio.newSound() . The AndroidAudio instance also manages the SoundPool .
public AndroidAudio(Activity activity) {
activity.setVolumeControlStream(AudioManager. STREAM_MUSIC );
this .assets=activity.getAssets();
this .soundPool= new SoundPool(20, AudioManager. STREAM_MUSIC , 0);
}
There are two reasons why we pass our game's Activity in the constructor: it allows us to
set the volume control of the media stream (we always want to do that), and it gives us an
AssetManager instance, which we will happily store in the corresponding class member.
The SoundPool is configured to play back 20 sound effects in parallel, which is adequate for
our needs.
public Music newMusic(String filename) {
try {
AssetFileDescriptor assetDescriptor=assets.openFd(filename);
return new AndroidMusic(assetDescriptor);
} catch (IOException e) {
throw new RuntimeException("Couldn't load music '"+filename+"'");
}
}
The newMusic() method creates a new AndroidMusic instance. The constructor of that class
takes an AssetFileDescriptor , which it uses to create an internal MediaPlayer (more on that
later). The AssetManager.openFd() method throws an IOException in case something goes
wrong. We catch it and rethrow it as a RuntimeException . Why not hand the IOException to
the caller? First, it would clutter the calling code considerably, so we would rather throw a
RuntimeException that does not have to be caught explicitly. Second, we load the music from
an asset file. It will only fail if we actually forget to add the music file to the assets/directory, or
if our music file contains false bytes. False bytes constitute unrecoverable errors since we need
that Music instance for our game to function properly. To avoid such an occurrence, we throw
RuntimeException s instead of checked exceptions in a few more places in the framework of
our game.
public Sound newSound(String filename) {
try {
AssetFileDescriptor assetDescriptor=assets.openFd(filename);
int soundId=soundPool.load(assetDescriptor, 0);
return new AndroidSound(soundPool, soundId);
} catch (IOException e) {
throw new RuntimeException("Couldn't load sound '"+filename+"'");
}
}
}
Finally, the newSound() method loads a sound effect from an asset into the SoundPool and returns
an AndroidSound instance. The constructor of that instance takes a SoundPool and the ID of the