hollow_view.java

public class CanvasView extends View {

    private Paint backgroundPaint = new Paint();
    private Paint paint = new Paint();

    public CanvasView(Context context) {
        super(context);
    }

    public CanvasView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public CanvasView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public void draw(Canvas canvas) {
        super.draw(canvas);
        setLayerType(View.LAYER_TYPE_HARDWARE, null);

        // draw all
        backgroundPaint.setColor(ContextCompat.getColor(getContext(), android.R.color.background_dark));
        canvas.drawRect(0, 0, canvas.getWidth(), canvas.getHeight(), backgroundPaint);

        // hollow a cirlce out of the black brackgroud
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
        canvas.drawCircle(getWidth() / 2, getHeight() / 2, 250, paint);
    }
}