Recyclerview返回顶部及分割线代码实现

public class SpacesItemDecoration extends RecyclerView.ItemDecoration {

    private int space;

    public SpacesItemDecoration(int space) {
        this.space=space;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        outRect.left=space;
        outRect.right=space;
        outRect.bottom=space;
            outRect.top=space;
    }

}

 //设置item之间的间隔
        SpacesItemDecoration decoration=new SpacesItemDecoration(10);
        recyclerView.addItemDecoration(decoration);

public abstract class RecyclerViewScrollDetector extends RecyclerView.OnScrollListener {

    private int mScrollThreshold;

    public abstract void onScrollUp();

    public abstract void onScrollDown();

    public abstract void onScrollTop();

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        //设置移动3后才触发事件
        setScrollThreshold(3);
        boolean isSignificantDelta = Math.abs(dy) > mScrollThreshold;
        if (isSignificantDelta) {
            if (dy > 0) {
                onScrollUp();
            } else {
                if(getScrolledDistance(recyclerView)>1000){
                    onScrollDown();
                }else{
                    onScrollTop();
                }
            }
        }
    }

    private int getScrolledDistance(RecyclerView recyclerView) {
        LinearLayoutManager layoutManager = (LinearLayoutManager)recyclerView.getLayoutManager();
        View firstVisibleItem = recyclerView.getChildAt(0);
        int firstItemPosition = layoutManager.findFirstVisibleItemPosition();
        int itemHeight = firstVisibleItem.getHeight();
        int firstItemBottom = layoutManager.getDecoratedBottom(firstVisibleItem);
        return (firstItemPosition + 1) * itemHeight - firstItemBottom;
    }

    public void setScrollThreshold(int scrollThreshold) {
        mScrollThreshold = scrollThreshold;
    }

  recyclerView.addOnScrollListener(new RecyclerViewScrollDetector() {
            @Override
            public void onScrollUp() {
                if(imageView.getVisibility()==View.VISIBLE){
                    imageView.setVisibility(View.INVISIBLE);
                }
            }

            @Override
            public void onScrollDown() {
                if(imageView.getVisibility()!=View.VISIBLE){
                    imageView.setVisibility(View.VISIBLE);
                }
            }
            //以滑进顶部识别区1000
            @Override
            public void onScrollTop() {
                if(imageView.getVisibility()==View.VISIBLE){
                    imageView.setVisibility(View.INVISIBLE);
                }
            }
        });