ActionBar黑色阴影渐变效果

heightMove = DisplayUtil.dip2px(this, 220);
this.actionBar = getActionBar();
this.actionBar.setDisplayHomeAsUpEnabled(false);
this.actionBar.setDisplayShowCustomEnabled(true);
View view = getLayoutInflater().inflate(R.layout.transparent_actionbar, null);
this.actionBar.setCustomView(view);
mActionBarBackgroundDrawable = getResources().getDrawable(R.drawable.red);
mActionBarBackgroundDrawable.setAlpha(0);

scrollView.setScrollViewListener(new ObservableScrollView.ScrollViewListener() {
    @Override
    public void onScrollChanged(ObservableScrollView scrollView, int x, int y, int oldx, int oldy) {
        int spot = layoutButton.getTop() - DisplayUtil.dip2px(mContext, 48);
        if (y <= spot) {
            layoutButtonTop.setVisibility(View.GONE);
        } else {
            layoutButtonTop.setVisibility(View.VISIBLE);
        }


        //ActionBar渐变效果
        final int headerHeight = heightMove - getActionBar().getHeight();
        final float ratio = (float) Math.min(Math.max(y, 0), headerHeight) / headerHeight;
        final int newAlpha = (int) (ratio * 255);
        mActionBarBackgroundDrawable.setAlpha(newAlpha);
        //ActionBar黑色阴影渐变效果
        int blackHeight = headerHeight / 2;
        float blackRatio = (float) Math.min(Math.max(y, 0), blackHeight) / blackHeight;
        int blackAlpha = 255 - (int) (blackRatio * 255);
        if (blackAlpha >= 0) {
            blackView.setAlpha(blackAlpha);
        }
        if (newAlpha > 60) {
            blackView.setVisibility(View.GONE);
        } else {
            blackView.setVisibility(View.VISIBLE);
        }

    }
});