при анализе данных JSON «нет книги» логика не работает в android

Question

Я использую GOOGLE_BOOK_API для анализа данных JSON. когда пользователь вводит ключевое слово в виде поиска, которое отсутствует в списке, тогда mEmptyStateTextView не работает, что говорит, что ни одна книга не найдена. ниже мой код.

BookActivity.java // подробнее книга

public class BookActivity extends AppCompatActivity { 

/** 
* URL for book data from the google book dataset 
*/ 
private static final String GOOGLE_REQUEST_SEARCH_URL = "https://www.googleapis.com/books/v1/volumes?maxResults=20&q="; 
View loadingIndicator; 
ArrayList<Book> books; 
ConnectivityManager connectivityManager; 
NetworkInfo networkInfo; 
/** 
* Adapter for the list of earthquakes 
*/ 
private BookAdapter mAdapter; 
private TextView mEmptyStateTextView; 

@Override 
protected void onSaveInstanceState(Bundle keepState) { 
    keepState.putParcelableArrayList("booklist", books); 
    Log.v("My Log message", "book is :" + books); 
    super.onSaveInstanceState(keepState); 
} 


@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    setContentView(R.layout.activity_book); 
    loadingIndicator = findViewById(R.id.loading_indicator); 
    loadingIndicator.setVisibility(View.GONE); 

    // Find a reference to the {@link ListView} in the layout 
    ListView bookListView = (ListView) findViewById(R.id.list); 

    mEmptyStateTextView = (TextView) findViewById(R.id.empty_view); 
    mEmptyStateTextView.setText(R.string.no_data); 
    bookListView.setEmptyView(mEmptyStateTextView); 

    // Create a new adapter that takes an empty list of books as input 
    mAdapter = new BookAdapter(this, new ArrayList<Book>()); 

    // Set the adapter on the {@link ListView} 
    // so the list can be populated in the user interface 
    bookListView.setAdapter(mAdapter); 

    if (savedInstanceState != null) { 
     books = savedInstanceState.getParcelableArrayList("booklist"); 
     mAdapter.addAll(books); 

    } else { 
     books = new ArrayList<>(); 

    } 
    bookListView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) { 
      Book currentBook = mAdapter.getItem(position); 

      Uri bookUri = Uri.parse(currentBook.getUrl()); 

      Intent websiteIntent = new Intent(Intent.ACTION_VIEW, bookUri); 

      startActivity(websiteIntent); 
     } 
    }); 


    /* if (networkInfo != null && networkInfo.isConnected()) { 

     BookAsyncTask task = new BookAsyncTask(); 
     task.execute(GOOGLE_REQUEST_SEARCH_URL); 
    } else { 

     loadingIndicator = findViewById(R.id.loading_indicator); 
     loadingIndicator.setVisibility(View.GONE); 

     mEmptyStateTextView.setText(R.string.no_internet_connection); 
    }*/ 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    MenuInflater inflater = getMenuInflater(); 
    inflater.inflate(R.menu.options_menu, menu); 

    SearchManager searchManager = 
      (SearchManager) getSystemService(Context.SEARCH_SERVICE); 

    MenuItem searchItem = menu.findItem(R.id.search); 
    final SearchView searchView = (SearchView) searchItem.getActionView(); 

    searchView.setSearchableInfo(searchManager.getSearchableInfo(getComponentName())); 
    searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() { 
     @Override 
     public boolean onQueryTextSubmit(String query) { 

      String urlQuery; 
      query = searchView.getQuery().toString(); 

      connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); 

      networkInfo = connectivityManager.getActiveNetworkInfo(); 
      if (networkInfo != null && networkInfo.isConnected()) { 

       BookAsyncTask task = new BookAsyncTask(); 
       task.execute(GOOGLE_REQUEST_SEARCH_URL); 

       if (!TextUtils.isEmpty(query)) { 

        String encodedQuery = ""; 
        try { 
         encodedQuery = URLEncoder.encode(query, "utf-8"); 
        } catch (UnsupportedEncodingException e) { 
         e.printStackTrace(); 
        } 
        urlQuery = GOOGLE_REQUEST_SEARCH_URL + encodedQuery + "&maxResults=10"; 

        //Toast.makeText(getApplicationContext(), urlQuery, Toast.LENGTH_SHORT).show(); 
        mAdapter.clear(); 
        mEmptyStateTextView.setText(""); // clear any message set previously 
        loadingIndicator.setVisibility(View.VISIBLE); // show loading during search 
        new BookAsyncTask().execute(urlQuery); 
       } 

      } else { 

       Toast.makeText(getApplicationContext(), "Network not available", Toast.LENGTH_SHORT).show(); 
      } 
      return true; 
     } 

     @Override 
     public boolean onQueryTextChange(String newText) { 

      return false; 
     } 
    }); 

    return true; 
} 

private class BookAsyncTask extends AsyncTask<String, Void, ArrayList<Book>> { 
    @Override 
    protected ArrayList<Book> doInBackground(String... urls) { 

     if (urls.length < 1 || urls[0] == null) { 
      return null; 
     } 

     ArrayList<Book> result = QueryUtils.fetchBook(urls[0]); 
     return result; 
    } 

    @Override 
    protected void onPostExecute(ArrayList<Book> result) { 

     loadingIndicator = findViewById(R.id.loading_indicator); 
     loadingIndicator.setVisibility(View.GONE); 

     mAdapter.clear(); 

     if (result == null) { 
      return; 
     } 
     if (result != null && !result.isEmpty()) { 
      books = result; 
      mAdapter.addAll(result); 
     } 

     mEmptyStateTextView.setText(R.string.no_book_found); 

    } 
} 

}

activity_book.xml

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="match_parent" 
android:layout_height="match_parent"> 

<!-- Layout for a list of books --> 
<ListView 
    android:id="@+id/list" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:orientation="vertical" 
    android:dividerHeight="0dp" 
    android:divider="@null"/> 

<!-- Empty view is only visible when the list has no items. --> 
<TextView 
    android:id="@+id/empty_view" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_centerInParent="true" 
    android:paddingLeft="@dimen/padding_left" 
    android:paddingRight="@dimen/padding_right" 
    android:textAppearance="?android:textAppearanceMedium"/> 

<!-- Loading indicator is only shown before the first load --> 
<ProgressBar 
    android:id="@+id/loading_indicator" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_centerInParent="true"/> 

</RelativeLayout> 

Answer 1

Вы звоните BookAsyncTask два раза выборки метода URL-адрес, первый бьет апи https://www.googleapis.com/books/v1/volumes?maxResults=20&q= (это неправильные параметры), а второй - с правильными параметрами.

И согласно андроиду директивам (more details) в отношении AsyncTask, только один экземпляр AsyncTask может быть выполнен в то время, так что второй правильный URL никогда не получает вызов, и вы получили ответ ударил первый удар, который ни одна книги не найден

Заменить onQueryTextSubmit полный метод с методом, описанным ниже,

public boolean onQueryTextSubmit(String query) { 

     String urlQuery; 
     query = searchView.getQuery().toString(); 

     connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); 

     networkInfo = connectivityManager.getActiveNetworkInfo(); 
     if (networkInfo != null && networkInfo.isConnected()) { 

      //BookAsyncTask task = new BookAsyncTask(); //Removing this and below will solve the problem 
      //task.execute(GOOGLE_REQUEST_SEARCH_URL);//Removing this will solve the problem 

      if (!TextUtils.isEmpty(query)) { 

       String encodedQuery = ""; 
       try { 
        encodedQuery = URLEncoder.encode(query, "utf-8"); 
       } catch (UnsupportedEncodingException e) { 
        e.printStackTrace(); 
       } 
       urlQuery = GOOGLE_REQUEST_SEARCH_URL + encodedQuery + "&maxResults=10"; 

       //Toast.makeText(getApplicationContext(), urlQuery, Toast.LENGTH_SHORT).show(); 
       mAdapter.clear(); 
       mEmptyStateTextView.setText(""); // clear any message set previously 
       loadingIndicator.setVisibility(View.VISIBLE); // show loading during search 
       new BookAsyncTask().execute(urlQuery); 
      } 

     } else { 

      Toast.makeText(getApplicationContext(), "Network not available", Toast.LENGTH_SHORT).show(); 
     } 
     return true; 
    } 

EDIT: Заканчивать очень хороший учебник по этим link который выборке и разбор данных JSON I nto JAVA с использованием рамки GSON