实现用户可见最大百分比的item查找

因项目需要仿微博播放列表，实现播放列表的蒙版覆盖切换，用户可见最大百分比的item的position查找

public class RecycleViewPercentItem {

    private VisibleItem mVisibleItem;
    private int percentPosition = -1;
    private int lastPercentPosition = -1;

    public RecycleViewPercentItem(VisibleItem mVisibleItem) {
        this.mVisibleItem = mVisibleItem;
    }
    //初始最大百分比的位置
    public void setPercentPosition(int percentPosition) {
        this.percentPosition = percentPosition;
    }
    //RecyclerView,列表的最大长度
    public void getItemVisible(RecyclerView recyclerView, int maxSize) {
        lastPercentPosition = percentPosition;
        LinearLayoutManager manager = (LinearLayoutManager) recyclerView.getLayoutManager();
        //获取可见item个数
        int childCount = manager.findLastVisibleItemPosition() - manager.findFirstVisibleItemPosition() + 1;
        //第一个可见item的位置
        int firstVisible = manager.findFirstVisibleItemPosition();
        Map<Integer, Integer> percents = new HashMap<>();
        for (int i = 0; i < childCount; i++) {
            //取出所有可见itemview
            View view = manager.findViewByPosition(firstVisible + i);
            int position = firstVisible + i;
            if (position >= maxSize) {
                break;
            }
            KLog.e("可见位置：" + position + "，可见百分比：" + getVisibilityPercents(view));
            percents.put(getVisibilityPercents(view), position);
        }
        if (percents.size() > 0) {
            //取出百分比最大的position
            Set<Integer> set = percents.keySet();
            percentPosition = percents.get(Collections.max(set));
        }
        if (lastPercentPosition == percentPosition) {
            return;
        }
        mVisibleItem.maxPercentPosition(percentPosition, lastPercentPosition);
    }

    private int getVisibilityPercents(View view) {
        Rect rect = new Rect();
        view.getLocalVisibleRect(rect);
        int height = view.getHeight();
        int percents = 100;
        if (rect.top == 0 && rect.bottom == height) {
            percents = 100;
        } else if (rect.top > 0) {
            percents = (height - rect.top) * 100 / height;
        } else if (rect.bottom > 0 && rect.bottom < height) {
            percents = rect.bottom * 100 / height;
        }
        return percents;
    }

    public interface VisibleItem {
        //当前可见最大百分比的position，上次可见最大百分比的position
        void maxPercentPosition(int percentPosition, int lastPercentPosition);
    }
}