设置滚动条显示隐藏

private void showScrollBar() {
    mViewDataBinding.recyclerSystemItem.getViewTreeObserver()
            .addOnScrollChangedListener(new ViewTreeObserver.OnScrollChangedListener() {
                @Override
                public void onScrollChanged() {
                    if (mViewDataBinding.recyclerSystemItem.canScrollVertically(1) &&
                            mViewDataBinding.recyclerSystemItem.computeVerticalScrollRange()
                                    >= mViewDataBinding.recyclerSystemItem.getHeight()) {
                        //可以滑动显示scrollbar
                    } else {
                        //不可以滑动隐藏scrollbar
                    }
                }
            });
}