android recyclerview下拉刷新时为什么会清空上一次的列表然后再显示新的数据？

Question

Adapter：List<Posts> mPosts;Context mContext;public MyRecycerAdapter(Context context, List<Posts> posts) {    mPosts = posts;    mContext = context;}public void addItem(int positionToAdd) {    mPosts.add(positionToAdd, new Posts());    notifyItemInserted(positionToAdd);}Volley Request：StringRequest stringRequest = new StringRequest(Request.Method.GET, jsonUrl,            new Response.Listener<String>() {                @Override                public void onResponse(String response) {                    mPostsJsonModel = new Gson().fromJson(response,                            PostsJsonModel.class);                    mPosts = mPostsJsonModel.getPosts();                }Activity下拉刷新：mMyRecycerAdapter.addItem(0);为什么刷新时会清空第一页，然后显示第二页？而不是直接把新请求的数据插入第一页。。。增加 mMyRecycerAdapter.notifyDataSetChanged();后刷新直接就崩溃了。崩溃信息：AndroidRuntime: FATAL EXCEPTION: main java.lang.NullPointerException at com.**..Adapter.MyRecycerAdapter.onBindViewHolder(MyRecycerAdapter.java:61)String imageUrl = mPosts.get(position).getAttachments().get(0).getImages().getThumbnail().getUrl();**是61行**public void onBindViewHolder(final NormalViewHolder holder, int position) {        String titleItem = mPosts.get(position).getTitle();        holder.mTextView.setText(titleItem);        String imageUrl = mPosts.get(position).getAttachments().get(0).getImages().getThumbnail().getUrl();}这是onCreateprotected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mRecyclerView = (RecyclerView) findViewById(R.id.recyclerview);        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));        mRecyclerView.setItemAnimator(new DefaultItemAnimator());        mRecyclerView.setHasFixedSize(true);        mMyRecycerAdapter = new MyRecycerAdapter(MainActivity.this,                mPosts);        mRecyclerView.setAdapter(mMyRecycerAdapter);把setAdapter放到onCreate中然后就不显示recyclerview了，是空白

Answer 1

因为你每次onResponse都重新new了adapter并setAdapter，之前的数据当然没有了，只有最新的数据。