I figured it out so I am answering my own question.
It cannot be done in XML, but it can be done in Java by overriding the onDraw() method of KeyboardView. This pointless example draws a small letter at the top of each key after the keys are drawn by the parent class:
public class MyKeyboardView extends KeyboardView {
@Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
Paint paint = new Paint();
paint.setTextAlign(Paint.Align.CENTER);
paint.setTextSize(25);
paint.setColor(Color.RED);
List<Key> keys = getKeyboard().getKeys();
for(Key key: keys) {
if(key.label != null)
canvas.drawText(key.label.toString(), key.x + (key.width/2), key.y + 25, paint);
}
}
}
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…