class MyItemDecoration extends RecyclerView.ItemDecoration {
    private int mOrientation = LinearLayout.VERTICAL;
    private Drawable mDivider;

    MyItemDecoration(Context context) {
        int[] rids = new int[]{android.R.attr.listDivider};//系统自带的属性，宽高各2dp
        TypedArray typedArray = context.obtainStyledAttributes(rids);
        mDivider = typedArray.getDrawable(0);
        typedArray.recycle();
    }

    void setOrientation(int orientation) {
        mOrientation = orientation;
    }

    int getOrientation() {
        return mOrientation;
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        ((LinearLayoutManager) parent.getLayoutManager()).setOrientation(mOrientation);
        if (mDivider != null) {
            //需要传入画布和当前recyclerview
            if (mOrientation == LinearLayout.HORIZONTAL) {
                drawHorizontal(c, parent);
            } else {
                drawVertical(c, parent);
            }
        }
    }

    //绘制竖直方向的横线
    private void drawVertical(Canvas c, RecyclerView parent) {
        int left = parent.getPaddingLeft();//横线左右随父容器
        int right = parent.getWidth() - parent.getPaddingRight();
        for (int i = 0; i < parent.getChildCount(); i++) {
            //遍历recyclerview的每个子view
            View child = parent.getChildAt(i);
            //分割线的top,left,right,bottom
            int top = child.getBottom();
            int bottom = child.getBottom() + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);//设置分割线的区域
            mDivider.draw(c);//绘制到画布
        }
    }

    //绘制水平方向的竖线
    private void drawHorizontal(Canvas c, RecyclerView parent) {
        int top = parent.getPaddingTop();//竖线上下随父容器
        int bottom = parent.getBottom();
        for (int i = 0; i < parent.getChildCount(); i++) {
            //遍历recyclerview的每个子view
            View child = parent.getChildAt(i);
            //分割线的top,left,right,bottom
            int left = child.getRight();
            Log.d("TAG", "LEFT:" + left);
            int right = left + mDivider.getIntrinsicWidth();
            mDivider.setBounds(left, top, right, bottom);//设置分割线的区域
            mDivider.draw(c);//绘制到画布
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State
            state) {
        super.getItemOffsets(outRect, view, parent, state);
        //item之间的位移量
        if (mOrientation == LinearLayout.HORIZONTAL) {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        } else {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        }
    }
}

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.jogger.animatorpathdemo.MainActivity">

    <Button
        android:id="@+id/btn_add"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="添加"/>

    <Button
        android:id="@+id/btn_reduce"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="移除"/>

    <Button
        android:id="@+id/btn_change"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="切换orientation"/>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_content"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>
</LinearLayout>

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private RecyclerView rv_content;
    private MyAdapter mAdapter;
    private Button btn_add;
    private Button btn_reduce;
    private Button btn_change;
    private int mPos;
    private MyItemDecoration mMyItemDecoration;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        rv_content = (RecyclerView) findViewById(R.id.rv_content);
        mAdapter = new MyAdapter(this);
        rv_content.setLayoutManager(new LinearLayoutManager(this));
        rv_content.setAdapter(mAdapter);
        rv_content.setItemAnimator(new DefaultItemAnimator());//默认添加动画
        mMyItemDecoration = new MyItemDecoration(this);
        mMyItemDecoration.setOrientation(LinearLayout.HORIZONTAL);//设置方向
        rv_content.addItemDecoration(mMyItemDecoration);
        btn_add = (Button) findViewById(R.id.btn_add);
        btn_reduce = (Button) findViewById(R.id.btn_reduce);
        btn_change = (Button) findViewById(R.id.btn_change);
        btn_add.setOnClickListener(this);
        btn_reduce.setOnClickListener(this);
        btn_change.setOnClickListener(this);
    }


    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn_add:
                mAdapter.addItem(mPos);
                mPos++;
                if (mPos > 50) {
                    mPos = 50;
                }
                break;
            case R.id.btn_reduce:
                mPos--;
                if (mPos < 0) {
                    mPos = 0;
                }
                mAdapter.removeItem(mPos);
                break;
            case R.id.btn_change:
                if (mMyItemDecoration.getOrientation() == LinearLayout.HORIZONTAL) {
                    mMyItemDecoration.setOrientation(LinearLayout.VERTICAL);//设置方向
                } else {
                    mMyItemDecoration.setOrientation(LinearLayout.HORIZONTAL);//设置方向
                }
                rv_content.addItemDecoration(mMyItemDecoration);
                break;
        }
    }
}

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
    private Context mContext;
    private List<String> mList;

    public MyAdapter(Context context) {
        mContext = context;
        mList = new ArrayList<>();
    }

    public void addItem(int pos) {
        mList.add(pos, "android--->" + pos);
        notifyItemInserted(pos);
    }

    public void removeItem(int pos) {
        mList.remove(pos);
        notifyItemChanged(pos);
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return new MyViewHolder(LayoutInflater.from(mContext).inflate(R.layout.rv_item, parent,
                false));
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.tv_content.setText(mList.get(position));
    }

    @Override
    public int getItemCount() {
        return mList.size();
    }

    class MyViewHolder extends RecyclerView.ViewHolder {
        TextView tv_content;

        MyViewHolder(View itemView) {
            super(itemView);
            tv_content = (TextView) itemView.findViewById(R.id.tv_content);
        }
    }
}