How to set different background of keys for Android Custom Keyboard

As an example, there's a small downloadable project that creates a custom numeric keyboard. To the CustomKeyboardView class there or to your own custom keyboard class, add a method like the following. It overrides the onDraw() method and draws the background of the key defined with code 7 (in this case the "0") red and all the other keys blue.

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    List<Key> keys = getKeyboard().getKeys();
    for (Key key : keys) {            
        if (key.codes[0] == 7) {
            Log.e("KEY", "Drawing key with code " + key.codes[0]);
            Drawable dr = (Drawable) context.getResources().getDrawable(R.drawable.red_tint);
            dr.setBounds(key.x, key.y, key.x + key.width, key.y + key.height);
            dr.draw(canvas);

        } else {
            Drawable dr = (Drawable) context.getResources().getDrawable(R.drawable.blue_tint);
            dr.setBounds(key.x, key.y, key.x + key.width, key.y + key.height);
            dr.draw(canvas);
        }            
    }
}

In this case, I didn't use 9-patch images, but just some simple 50% transparent square images and achieved an effect where the existing buttons are merely tinted with the colors I wanted. To get a more custom result, I could make my background drawables 9-patch images and do the following. Note that the two keys with icons don't render correctly because the icons aren't defined as 9-patch images and I didn't make any special effort to allow them to scale well for this example. I also didn't address the use of different images/effects for the various states for the keys; others have shown how to do that.

@Override
public void onDraw(Canvas canvas) {
    // super.onDraw(canvas);

    List<Key> keys = getKeyboard().getKeys();
    for (Key key : keys) {
        if (key.codes[0] == 7) {
            NinePatchDrawable npd
                = (NinePatchDrawable) context.getResources().getDrawable(R.drawable.red_key);
            npd.setBounds(key.x, key.y, key.x + key.width, key.y + key.height);
            npd.draw(canvas);

        } else {
            NinePatchDrawable npd
                = (NinePatchDrawable) context.getResources().getDrawable(R.drawable.blue_key);
            npd.setBounds(key.x, key.y, key.x + key.width, key.y + key.height);
            npd.draw(canvas);
        }

        Paint paint = new Paint();
        paint.setTextAlign(Paint.Align.CENTER);
        paint.setTextSize(48);
        paint.setColor(Color.GRAY);

        if (key.label != null) {
            canvas.drawText(key.label.toString(), key.x + (key.width / 2),
                            key.y + (key.height / 2), paint);
        } else {
            key.icon.setBounds(key.x, key.y, key.x + key.width, key.y + key.height);
            key.icon.draw(canvas);
        }
    }
}    

I created a keyboard app in which I use the KeyBackground property in KeyboardView, like so:

<KeyboardView android:keyBackground="@drawable/buttonbgselector" .../>

To do this dynamically I use the following code:

@Override 
public View onCreateInputView() {
    mInputView = (KeyboardView) getLayoutInflater().inflate(R.layout.input, null);
    mInputView.setBackgroundResource(R.drawable.buttonbgselector);
    mInputView.setOnKeyboardActionListener(this);
    mInputView.setKeyboard(mQwertyKeyboard);
    return mInputView;
}