RecylerView 在TV端焦点循环轮切功能

功能描述：   Android TV端通过遥控器控制focus在RecyclerView移动，当焦点处于第一个item，再向上按，则焦点跳至最后一个。同理，在最后一个，再向下按跳至第一个。（RecycleView垂直布局）

解决思路：   1、 跳转时，让RecycleView做smoothScrollToPosition(int position)操作，position为第一个或者最后一个item位置。

                        2、跳转后，获取当前屏幕第一个可见或最有一个可见view ，请求焦点即可。

部分代码如下：

1.监听上下键,做滚动操作

holder.itemView.setOnKeyListener(new View.OnKeyListener() {
    @Override
    public boolean onKey(View v, int keyCode, KeyEvent event) {
        int action = event.getAction();
        switch (keyCode) {
            case KeyEvent.KEYCODE_DPAD_UP:
                int positionUp  =  (int) v.getTag();
                if (action == KeyEvent.ACTION_DOWN) {
                    if (positionUp <=  0) {
                        recyclerView.smoothScrollToPosition(getItemCount() - 1);
                        return true;
                    }
                }
                break;

            case KeyEvent.KEYCODE_DPAD_DOWN:
                int positionDown = (int) v.getTag();
                if (action == KeyEvent.ACTION_DOWN) {
                    if (positionDown >= getItemCount() - 1) {
                        recyclerView.smoothScrollToPosition(0);
                        return true;
                    }
                }
                break;
    }
});

2.监听滚动。这里需要注意的是，通过RecycleView的getChildAt()获取view可能为空。可以获取RecyleView对应的LayoutManager(这里是LinearLayoutManager),然后通过manager的findFirstCompletelyVisibleItemPosition()获取当前屏幕第一个或者findLastCompletelyVisibleItemPosition()获取当前屏幕的最后一个position。 最后通过position找到view，再requestFocus().

recycleView.setOnScrollListener(new RecyclerView.OnScrollListener() {

    //向上或者向下滚动
  boolean toLast = false;
    booleantoFirst = false;

    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        super.onScrollStateChanged(recyclerView, newState);
        if (newState == RecyclerView.SCROLL_STATE_IDLE) {
            scroolChange(recyclerView, toFirst, toLast);
        }
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        if (dy > 0) {
           toLast = true;
        } else {
           toFirst = true;
        }
    }
});

public void scroolChange(RecyclerView recyclerView, boolean toFirst, boolean toLast) {
    LinearLayoutManager manager = (LinearLayoutManager) recyclerView.getLayoutManager();
    int lastVisibleItem = manager.findLastCompletelyVisibleItemPosition();
    int firstVisibleItem = manager.findFirstCompletelyVisibleItemPosition();
    int totalItemCount = manager.getItemCount();


    //向下滚动,到底部
    if (lastVisibleItem == (totalItemCount - 1) && toLast) {
        View view = recyclerView.getChildAt(lastVisibleItem);
        LinearLayoutManager llM = (LinearLayoutManager) recyclerView.getLayoutManager();
        if (view != null) {
            view.requestFocus();
        } else if (llM.findViewByPosition(lastVisibleItem) != null) {
            llM.findViewByPosition(lastVisibleItem).requestFocus();
        } else {
            recyclerView.requestFocus();
        }
    }

    //向上滚动,到顶部
    if (firstVisibleItem == 0 && toFirst) {
        View view =recyclerView.getChildAt(firstVisibleItem);
        LinearLayoutManager llM = (LinearLayoutManager) recyclerView.getLayoutManager();
        if (view != null) {
            view.requestFocus();
        } else if (llM.findViewByPosition(firstVisibleItem) != null) {
            llM.findViewByPosition(firstVisibleItem).requestFocus();
        } else {
            recyclerView.requestFocus();
        }
    }
}