【已解决】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？而不是直接插入新数据？

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();}

Posts Model：

public class Posts {

public List<Attachments> attachments;

public List<Attachments> getAttachments() {
    return attachments;
}

public void setAttachments(List<Attachments> attachments) {
    this.attachments = attachments;
}
}

Attachments Model：

public class Attachments {
private Images images;

public Images getImages() {
    return images;
}

public void setImages(Images images) {
    this.images = images;
}
}

Images Model：

public class Images {
private Thumbnail thumbnail;

public Thumbnail getThumbnail() {
    return thumbnail;
}

public void setThumbnail(Thumbnail thumbnail) {
    this.thumbnail = thumbnail;
}
}

Thumbnail Model：

public class Thumbnail {

private String url;


public void setUrl(String url) {
    this.url = url;
}

public String getUrl() {
    return url;
}
}

这是onCreate

protected 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。