@Override
    protected synchronized void onDraw(Canvas canvas) {
        if (!isLollipopOrGreater) {
            mRipple.draw(canvas);
        }
        super.onDraw(canvas);
        mTrack.draw(canvas);
        mScrubber.draw(canvas);
        mThumb.draw(canvas);
    }
When the {@link DiscreteSeekBar} value changes this method is called
<p>
Subclasses may override this to add functionality around this event
without having to specify a {@link OnProgressChangeListener}
</p>
app/src/main/java/com/duan/musicoco/view/discreteseekbar/DiscreteSeekBar.java