recycleview实现循环垂直滚动

要实现循环垂直滚动，可以使用RecyclerView和LayoutManager的组合。其中，LayoutManager负责控制RecyclerView中子项的排列方式，而RecyclerView则负责显示和回收子项。

具体实现步骤如下：

1. 创建一个自定义的LayoutManager，继承自LinearLayoutManager。

2. 在LayoutManager的onLayoutChildren()方法中，对子项进行循环布局。

3. 在RecyclerView的Adapter中，重写getItemCount()方法，返回一个很大的值，比如Integer.MAX_VALUE，以实现无限循环。

4. 在RecyclerView的onScrollStateChanged()方法中，当滚动状态为SCROLL_STATE_IDLE（即停止滚动）时，判断当前可见的子项是否为第一项或最后一项，如果是，则通过scrollToPosition()方法将RecyclerView的滚动位置调整到中间位置。

下面是一个简单的示例代码：

public class LoopLinearLayoutManager extends LinearLayoutManager {

    public LoopLinearLayoutManager(Context context) {
        super(context);
    }

    public LoopLinearLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
    }

    @Override
    public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
        super.onLayoutChildren(recycler, state);
        if (getItemCount() > 0) {
            int currentPosition = getCurrentPosition();
            int offset = getOffsetToCenter(currentPosition);
            if (offset != 0) {
                scrollBy(0, offset);
            }
        }
    }

    private int getCurrentPosition() {
        int currentPosition = findFirstVisibleItemPosition();
        if (currentPosition < 0) {
            currentPosition = 0;
        }
        return currentPosition;
    }

    private int getOffsetToCenter(int position) {
        View view = findViewByPosition(position);
        if (view == null) {
            return 0;
        }
        int viewHeight = getDecoratedMeasuredHeight(view);
        int viewCenter = getDecoratedTop(view) + viewHeight / 2;
        int center = getHeight() / 2;
        return viewCenter - center;
    }
}

public class LoopAdapter extends RecyclerView.Adapter<LoopAdapter.ViewHolder> {

    private static final int ITEM_COUNT = Integer.MAX_VALUE;
    private List<String> mData;

    public LoopAdapter(List<String> data) {
        mData = data;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_layout, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        holder.mTextView.setText(mData.get(position % mData.size()));
    }

    @Override
    public int getItemCount() {
        return ITEM_COUNT;
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {

        public TextView mTextView;

        public ViewHolder(View itemView) {
            super(itemView);
            mTextView = itemView.findViewById(R.id.text_view);
        }
    }
}

public class MainActivity extends AppCompatActivity {

    private RecyclerView mRecyclerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mRecyclerView = findViewById(R.id.recycler_view);
        mRecyclerView.setLayoutManager(new LoopLinearLayoutManager(this));
        mRecyclerView.setAdapter(new LoopAdapter(Arrays.asList("A", "B", "C", "D", "E", "F")));
    }
}

这样就可以实现循环垂直滚动了。