java - 使用 RecyclerView 并从 Web 服务获取信息但不显示答案并且我没有收到任何错误 为什么？

Question

public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<List<BookData>> {
    private static final String GOOGLEBOOKURL = "https://www.googleapis.com/books/v1/volumes?q=search+terms";
    private static final String TAG = "Mainactivity";
  private   RecyclerView recyclerview;
    private RecyclerAdapter recyclerAdapter;
    private static final int BOOK_LOADER_ID = 1;


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

        ArrayList<BookData> arrayList = new ArrayList<>();
        recyclerAdapter = new RecyclerAdapter(this,arrayList);
        recyclerview = (RecyclerView)findViewById(R.id.recyclerView);
       recyclerview.setLayoutManager(new LinearLayoutManager(this));
        recyclerview.setAdapter(recyclerAdapter);

        LoaderManager loaderManager = getSupportLoaderManager();
        Log.i(TAG, "Now calling initLoader");
        loaderManager.initLoader(BOOK_LOADER_ID, null, this);


        DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(this,DividerItemDecoration.VERTICAL);
        recyclerview.addItemDecoration(dividerItemDecoration);


    }

    @NonNull
    @Override
    public Loader<List<BookData>> onCreateLoader(int id, @Nullable Bundle args) {
        Log.i(TAG,"Problem with onCreateloader");
        return new BookLoader(MainActivity.this,GOOGLEBOOKURL);
    }

    @Override
    public void onLoadFinished(@NonNull Loader<List<BookData>> loader, List<BookData> data) {
        recyclerAdapter.clear();
        if (data != null && !data.isEmpty()) {
            recyclerAdapter.addAll(data);
        }
    }

    @Override
    public void onLoaderReset(@NonNull Loader<List<BookData>> loader) {
        recyclerAdapter.clear();
        Log.i(TAG, "Now loader is resetting");
    }
}

适配器

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

    ArrayList<BookData> mArrayList;
    Context mContext;

    public RecyclerAdapter(Context context, ArrayList<BookData> arrayList) {
        mArrayList = arrayList;
        mContext = context;

    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        ViewHolder viewHolder;
        LayoutInflater layoutInflater=LayoutInflater.from(parent.getContext());
       View v = layoutInflater.inflate(R.layout.rowrepresent,parent,false);
       viewHolder = new ViewHolder(v);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        BookData currentPosition = mArrayList.get(position);
      //  holder.authorname.setText(currentPosition.getAuthorName());
        holder.titlename.setText(currentPosition.getTitleName());
      //  holder.mImageView.setImageResource(Integer.parseInt(currentPosition.getImage()));
    }

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

    public static class ViewHolder extends RecyclerView.ViewHolder{

        ImageView mImageView;
        TextView titlename,authorname;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
          //  mImageView = (ImageView)itemView.findViewById(R.id.bookImage);
           titlename=(TextView)itemView.findViewById(R.id.titleName);
          //  authorname=(TextView)itemView.findViewById(R.id.authorName);
        }
    }
    public void clear() {
        if (mArrayList != null && !mArrayList.isEmpty()) {
            int size = mArrayList.size();
            mArrayList.clear();
            notifyItemRangeRemoved(0, size);
        }
    }

    public void addAll(List<BookData> data){
          mArrayList.addAll(data);
    }
}

网络

public class Network {
    private static final String TAG = "Network";

    public static ArrayList<BookData> extractbooksfromurl(String requesturl){
        ArrayList<BookData> BookDetails;
        URL url = createUrl(requesturl);

        String jsonresponse = null;
        try {
            jsonresponse = makeHttprequest(url);
        } catch (IOException e) {
            Log.e(TAG, "Error closing input stream", e);
        }

        BookDetails = extractInfojson(jsonresponse);
        return BookDetails;
    }

    private static URL createUrl(String requestUrl) {
        URL url = null;
        try {
            url = new URL(requestUrl);
        } catch (MalformedURLException e) {
            Log.e(TAG, "The problem with URL", e);
        }
        return url;
    }

    private static String makeHttprequest(URL url) throws IOException {
        String jsonresponse = "";
        if (url == null) {
            return jsonresponse;
        }
        HttpURLConnection urlConnection = null;
        InputStream inputStream = null;
        try {
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.setConnectTimeout(1000);
            urlConnection.setReadTimeout(1500);
            urlConnection.connect();
            if (urlConnection.getResponseCode() == 200) {
                inputStream = urlConnection.getInputStream();
                jsonresponse = readfromstream(inputStream);
            } else {
                Log.e(TAG, "Error response code:" + urlConnection.getResponseCode());
            }
        } catch (IOException e) {
            Log.e(TAG, "problem with MakeHttprequest method", e);
        } finally {
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
            if (inputStream != null) {
                inputStream.close();
            }
        }
        return jsonresponse;
    }

    private static String readfromstream(InputStream inputStream)throws IOException {
        StringBuilder output = new StringBuilder();
        if (inputStream!= null){
            InputStreamReader reader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
            BufferedReader bufferedReader = new BufferedReader(reader);
            try {
                String line = bufferedReader.readLine();
                while (line!=null ){
                    output.append(line);
                    line = bufferedReader.readLine();
                }

            } catch (IOException e) {
                Log.e(TAG,"Problem in readfromstream method",e);
            }
        } return output.toString();

    }
    public  static ArrayList<BookData> extractInfojson(String bookListData){
        if (TextUtils.isEmpty(bookListData)){
            return  null;
        }
        ArrayList<BookData> arrayListnew = new ArrayList<>();
        String authorsName = "";
        String title;
        String images;
        try {
            JSONObject jsonRootObject = new JSONObject(bookListData);
            JSONArray jsonArray = jsonRootObject.optJSONArray("item");
            if (jsonArray != null) {
                for (int i = 0; i<jsonArray.length(); i++){
                    JSONObject jsonObject = jsonArray.optJSONObject(i);
                    JSONObject volumeinfo = jsonObject.getJSONObject("volumeInfo");
                  /* JSONArray authors_list ;
                   if (volumeinfo.has("authors")){
                      authors_list = volumeinfo.getJSONArray("authors");
                       for (int y=0;y<authors_list.length();y++)
                           authorsName = authors_list.getString(y);
                   }else{
                       authorsName ="No Author";
                   }
                    title = volumeinfo.getString("title").toString();
                    JSONObject image = volumeinfo.getJSONObject("imageLinks");
                           images = image.getString("thumbnail").toString();*/
                   title = volumeinfo.getString("title").toString();
                    arrayListnew.add(new BookData(title));
                }
            }

        } catch (JSONException e) {
            Log.e(TAG,"problem in parsing the data",e);
        }
    return arrayListnew;
    }


}

日志猫

2020-11-21 11:27:29.407 12457-12457/com.example.booklistapp I/Mainactivity: Now calling initLoader
2020-11-21 11:27:29.407 12457-12457/com.example.booklistapp I/Mainactivity: Problem with onCreateloader
2020-11-21 11:27:29.412 12457-12457/com.example.booklistapp I/BookLoader: Now onStartLoading method
2020-11-21 11:27:29.417 12457-12472/com.example.booklistapp I/BookLoader: Now LoadinBackground method
2020-11-21 11:27:29.426 12457-12472/com.example.booklistapp D/NetworkSecurityConfig: No Network Security Config specified, using platform default
2020-11-21 11:27:29.496 12457-12473/com.example.booklistapp I/OpenGLRenderer: Initialized EGL, version 1.4
2020-11-21 11:27:29.496 12457-12473/com.example.booklistapp D/OpenGLRenderer: Swap behavior 1
2020-11-21 11:27:29.496 12457-12473/com.example.booklistapp W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
2020-11-21 11:27:29.496 12457-12473/com.example.booklistapp D/OpenGLRenderer: Swap behavior 0
2020-11-21 11:27:29.575 12457-12473/com.example.booklistapp D/EGL_emulation: eglCreateContext: 0x9b827520: maj 2 min 0 rcv 2
2020-11-21 11:27:29.688 12457-12473/com.example.booklistapp D/EGL_emulation: eglMakeCurrent: 0x9b827520: ver 2 0 (tinfo 0x9b89ad10)
2020-11-21 11:27:29.733 12457-12473/com.example.booklistapp D/EGL_emulation: eglMakeCurrent: 0x9b827520: ver 2 0 (tinfo 0x9b89ad10)

SomeBody 帮我解决这个问题，我没有收到任何错误但仍然没有显示答案？为什么？
谢谢你。

Answer 1

在您的 Recyclerview适配器 addAll方法，添加到数组后调用 notifyDataSetChanged()
像这样:

public void addAll(List<BookData> data) {
      mArrayList.addAll(data);
      notifyDataSetChanged();
}

更新:
根据评论，当您使用虚拟数据时，代码可以工作，这表明您的网络请求逻辑中存在另一个问题。
您可以通过在方法或代码行中放置各种断点来调试您的应用程序，以帮助确定您的代码逻辑未按预期运行的位置。 https://developer.android.com/studio/debug
您的任何其他问题都应该在一个新问题中，因为这个问题已经真正解决了。
我还建议使用像 Volley 这样的库这将大大简化您的网络请求。具体见 Making a standard request in Volley