private void placeBall() {
        ViewHelper.setX(ball, getHeight() / 2 - ball.getWidth() / 2);
        ball.xIni = ViewHelper.getX(ball);
        ball.xFin = getWidth() - getHeight() / 2 - ball.getWidth() / 2;
        ball.xCen = getWidth() / 2 - ball.getWidth() / 2;
        placedBall = true;
    }
Make a dark color to press effect

@return
MaterialDesignLibrary/MaterialDesign/src/main/java/com/gc/materialdesign/views/Slider.java