RecyclerView制定位置滑动置顶，并实现头部悬停

private void smoothMoveToPosition(final int position) {
//获取第一个跟最后一个可见item
int firstItem = reGoods.getChildLayoutPosition(reGoods.getChildAt(0));
int lastItem = reGoods.getChildLayoutPosition(reGoods.getChildAt(reGoods.getChildCount() - 1));
if (position < firstItem) {
// 如果要跳转的位置在第一个可见项之前，则smoothScrollToPosition可以直接跳转
reGoods.smoothScrollToPosition(position);
} else if (position <= lastItem) {
// 如果要跳转的位置在第一个可见项之后，且在最后一个可见项之前
// smoothScrollToPosition根本不会动，此时调用smoothScrollBy来滑动到指定位置
int movePosition = position - firstItem;
if (movePosition >= 0 && movePosition < reGoods.getChildCount()) {
int top = reGoods.getChildAt(movePosition).getTop();
reGoods.smoothScrollBy(0, top);
}
} else {
// 如果要跳转的位置在最后可见项之后，则先调用smoothScrollToPosition将要跳转的位置滚动到可见位置
// 再通过onScrollStateChanged控制再次调用smoothMoveToPosition，进入上一个控制语句
reGoods.smoothScrollToPosition(position);
mShouldScroll = true;
mToPosition = position;
}
}

private RecyclerView.OnScrollListener mOnScrollListener = new RecyclerView.OnScrollListener() {
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
//找到第二个item 离顶部距离 小于头部高度
View view = linearLayoutManager.findViewByPosition(mCurrentPosition + 1);
if (view != null) {
//如果小于等于 view的高度
if (view.getTop() <= mSuspensionHeight) {
//设置悬停view的位置
tvGroup.setY(-(mSuspensionHeight - view.getTop()));
} else {
//否则设置悬停就在顶部
tvGroup.setY(0);
}
}
//当前位置不等于第一个可见位置  更新悬停view
if (mCurrentPosition != linearLayoutManager.findFirstVisibleItemPosition()) {
//当前位置为第一个可见位置
mCurrentPosition = linearLayoutManager.findFirstVisibleItemPosition();
//头部悬停
tvGroup.setY(0);
if (!change) {
typesAdapter.setSelect(mCurrentPosition);
}
tvGroup.setText(goodsGroups.get(mCurrentPosition).getGroupName());
}
}

@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
//测量头部悬停view的高度
mSuspensionHeight = tvGroup.getHeight();
if (newState == RecyclerView.SCROLL_STATE_IDLE) {
//是否需要二次滚动
if (mShouldScroll) {
mShouldScroll = false;
//重新滚动
smoothMoveToPosition(mToPosition);
} else {
change = false;
}

}
}
};