Firebase Query Android

Question

我正在尝试使用特定newspaper_id查询新闻节点中的最后一项。 基本上，我希望始终使用新闻的ID作为查询来获取特定报纸的最新消息。查询是在FirebaseRecyclerAdpter populateViewHolder((中完成的，我得到了

java.lang.ArrayIndexOutOfBoundsException： length=0; index=-1 at java.util.ArrayList.get(ArrayList.java：310( at com.simpumind.e_tech_news.adapter.VendorNewAdapter$1.onDataChange(VendorNewAdapter.java：100(

 {
  "news": {
    "-HDRKDDGKSD56": {
          "caption" : "Hail Mary",
          "content" : "some  contents"
          "newspaper_id" : "-Kg9UvxyiuI4G3r6fCgU",
          thumbnail: "some base64 encoded image"
    },

 "newspaper": {
     "-Kg9UvxyiuI4G3r6fCgU" : {
            "content_provider" : 1,
            "cost" : "200",
            "logo" : "some base64 encoded image"
            "user": "The user"
    }
 }

这就是我尝试过的

@Override
protected void populateViewHolder(final NewsPaperHolder viewHolder, NewsPaper model, int position) {
    viewHolder.vendorName.setText(model.getPaper_name());
    mDatabaseRef = FirebaseDatabase.getInstance().getReference().child("news");
   String oneChildRef = getRef(position).getKey();
    mDatabaseRef.orderByChild("newspaper_id")
            .equalTo(oneChildRef)
            .addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

                List<News> newsList = new ArrayList();
                for (DataSnapshot d : dataSnapshot.getChildren()){
                    News n = d.getValue(News.class);
                    newsList.add(n);
                }
            newsList.toString();
                News news = newsList.get(newsList.size() -  1);
               updateUI(viewHolder, news);
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });

    Picasso.with(context).load(model.getLogo()).into(viewHolder.vendorIcon);
}

public void updateUI(NewsPaperHolder holder, News news){
    holder.firstNewsTitle.setText(news.getCaption());
    Picasso.with(context).load(news.getThumbnail()).into(holder.firstNewsImage);
}

新闻

public class News {
public String caption;
public String content;
public String newspaper_id;
public String thumbnail;
public String user;

public News(){
}
public News(String caption, String content, String newspaper_id, String thumbnail, String user) {
    this.caption = caption;
    this.content = content;
    this.newspaper_id = newspaper_id;
    this.thumbnail = thumbnail;
    this.user = user;
}
public String getCaption() {
    return caption;
}
public void setCaption(String caption) {
    this.caption = caption;
}
public String getContent() {
    return content;
}
public void setContent(String content) {
    this.content = content;
}
public String getNewspaper_id() {
    return newspaper_id;
}
public void setNewspaper_id(String newspaper_id) {
    this.newspaper_id = newspaper_id;
}
    public String getThumbnail() {
      return thumbnail;
    }
    public void setThumbnail(String thumbnail) {
       this.thumbnail = thumbnail;
    }
}

Answer 1

可能是在数据库不包含子数据库时遇到该错误。尝试通过以下方式逃避它：

public void onDataChange(DataSnapshot dataSnapshot) {
    ...
    if (newsList.size() > 0) {
        News news = newsList.get(newsList.size() - 1);
        updateUI(viewHolder, news);
    }
}

希望这有帮助