I'm trying to follow the course from Udacity. Now I'm stuck in lesson 4C with Loaders, I’m doing everything as it says, but the result is not that. When I run the application, weather data should be displayed in the ListView, but I only see a blank screen. To activate, or the leaf of the fragment is empty? Here is the MainActivity class:

public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction(); MainFragment mainFragment = new MainFragment(); fragmentTransaction.add(R.id.FragmentContainer,mainFragment); fragmentTransaction.commit(); } }

class MainFragment:

 public class MainFragment extends Fragment implements android.app.LoaderManager.LoaderCallbacks<Cursor> { private static final int FORECAST_LOADER = 0; private ForecastAdapter mForecastAdapter; public MainFragment() { } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); getLoaderManager().initLoader(FORECAST_LOADER,null,this); setHasOptionsMenu(true); } @Override public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) { inflater.inflate(R.menu.forecast_fragment, menu); } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); if (id == R.id.action_refresh) { updateWeather(); return true; } return super.onOptionsItemSelected(item); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // The ArrayAdapter will take data from a source and // use it to populate the ListView it's attached to. View rootView = inflater.inflate(R.layout.fragment_main, container, false); mForecastAdapter = new ForecastAdapter(getActivity(),null,0); ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast); listView.setAdapter(mForecastAdapter); return rootView; } private void updateWeather() { FetchWeatherTask weatherTask = new FetchWeatherTask(getActivity()); String location = Utility.getPreferredLocation(getActivity()); weatherTask.execute(location); } @Override public void onStart() { super.onStart(); updateWeather(); } @Override public android.content.Loader<Cursor> onCreateLoader(int id, Bundle args) { String locationSetting = Utility.getPreferredLocation(getActivity()); String sortOrder = WeatherContract.WeatherEntry.COLUMN_DATE + " ASC"; Uri weatherForLocationUri = WeatherContract.WeatherEntry.buildWeatherLocationWithStartDate( locationSetting, System.currentTimeMillis()); return new CursorLoader(getActivity(), weatherForLocationUri, null, null, null, sortOrder); } @Override public void onLoadFinished(android.content.Loader<Cursor> loader, Cursor data) { mForecastAdapter.swapCursor(data); } @Override public void onLoaderReset(android.content.Loader<Cursor> loader) { mForecastAdapter.swapCursor(null); } }

and the class FetchWeatherTask:

 public class FetchWeatherTask extends AsyncTask<String, Void, Void> { private static final String OPEN_WEATHER_MAP_API_KEY ="85240dd016c5d1cb4e1badfb919aaae4" ; private final String LOG_TAG = FetchWeatherTask.class.getSimpleName(); private final Context mContext; public FetchWeatherTask(Context context) { mContext = context; } private boolean DEBUG = true; /** * Helper method to handle insertion of a new location in the weather database. * * @param locationSetting The location string used to request updates from the server. * @param cityName A human-readable city name, eg "Mountain View" * @param lat the latitude of the city * @param lon the longitude of the city * @return the row ID of the added location. */ long addLocation(String locationSetting, String cityName, double lat, double lon) { long locationId; Cursor locationCursor = mContext.getContentResolver().query( WeatherContract.LocationEntry.CONTENT_URI, new String[]{WeatherContract.LocationEntry._ID}, WeatherContract.LocationEntry.COLUMN_LOCATION_SETTING + " = ?", new String[]{locationSetting}, null ); if(locationCursor.moveToFirst()){ int locationIdIndex = locationCursor.getColumnIndex(WeatherContract.LocationEntry._ID); locationId = locationCursor.getLong(locationIdIndex); } else{ ContentValues locationValues = new ContentValues(); locationValues.put(WeatherContract.LocationEntry.COLUMN_CITY_NAME,cityName); locationValues.put(WeatherContract.LocationEntry.COLUMN_LOCATION_SETTING,locationSetting); locationValues.put(WeatherContract.LocationEntry.COLUMN_COORD_LAT,lat); locationValues.put(WeatherContract.LocationEntry.COLUMN_COORD_LONG,lon); } return -1; } private String[] getWeatherDataFromJson(String forecastJsonStr, String locationSetting) throws JSONException { // Now we have a String representing the complete forecast in JSON Format. // Fortunately parsing is easy: constructor takes the JSON string and converts it // into an Object hierarchy for us. // These are the names of the JSON objects that need to be extracted. // Location information final String OWM_CITY = "city"; final String OWM_CITY_NAME = "name"; final String OWM_COORD = "coord"; // Location coordinate final String OWM_LATITUDE = "lat"; final String OWM_LONGITUDE = "lon"; // Weather information. Each day's forecast info is an element of the "list" array. final String OWM_LIST = "list"; final String OWM_PRESSURE = "pressure"; final String OWM_HUMIDITY = "humidity"; final String OWM_WINDSPEED = "speed"; final String OWM_WIND_DIRECTION = "deg"; // All temperatures are children of the "temp" object. final String OWM_TEMPERATURE = "temp"; final String OWM_MAX = "max"; final String OWM_MIN = "min"; final String OWM_WEATHER = "weather"; final String OWM_DESCRIPTION = "main"; final String OWM_WEATHER_ID = "id"; try { JSONObject forecastJson = new JSONObject(forecastJsonStr); JSONArray weatherArray = forecastJson.getJSONArray(OWM_LIST); JSONObject cityJson = forecastJson.getJSONObject(OWM_CITY); String cityName = cityJson.getString(OWM_CITY_NAME); JSONObject cityCoord = cityJson.getJSONObject(OWM_COORD); double cityLatitude = cityCoord.getDouble(OWM_LATITUDE); double cityLongitude = cityCoord.getDouble(OWM_LONGITUDE); long locationId = addLocation(locationSetting, cityName, cityLatitude, cityLongitude); // Insert the new weather information into the database Vector<ContentValues> cVVector = new Vector<ContentValues>(weatherArray.length()); // OWM returns daily forecasts based upon the local time of the city that is being // asked for, which means that we need to know the GMT offset to translate this data // properly. // Since this data is also sent in-order and the first day is always the // current day, we're going to take advantage of that to get a nice // normalized UTC date for all of our weather. Time dayTime = new Time(); dayTime.setToNow(); // we start at the day returned by local time. Otherwise this is a mess. int julianStartDay = Time.getJulianDay(System.currentTimeMillis(), dayTime.gmtoff); // now we work exclusively in UTC dayTime = new Time(); for(int i = 0; i < weatherArray.length(); i++) { // These are the values that will be collected. long dateTime; double pressure; int humidity; double windSpeed; double windDirection; double high; double low; String description; int weatherId; // Get the JSON object representing the day JSONObject dayForecast = weatherArray.getJSONObject(i); // Cheating to convert this to UTC time, which is what we want anyhow dateTime = dayTime.setJulianDay(julianStartDay+i); pressure = dayForecast.getDouble(OWM_PRESSURE); humidity = dayForecast.getInt(OWM_HUMIDITY); windSpeed = dayForecast.getDouble(OWM_WINDSPEED); windDirection = dayForecast.getDouble(OWM_WIND_DIRECTION); // Description is in a child array called "weather", which is 1 element long. // That element also contains a weather code. JSONObject weatherObject = dayForecast.getJSONArray(OWM_WEATHER).getJSONObject(0); description = weatherObject.getString(OWM_DESCRIPTION); weatherId = weatherObject.getInt(OWM_WEATHER_ID); // Temperatures are in a child object called "temp". Try not to name variables // "temp" when working with temperature. It confuses everybody. JSONObject temperatureObject = dayForecast.getJSONObject(OWM_TEMPERATURE); high = temperatureObject.getDouble(OWM_MAX); low = temperatureObject.getDouble(OWM_MIN); ContentValues weatherValues = new ContentValues(); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_LOC_KEY, locationId); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_DATE, dateTime); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_HUMIDITY, humidity); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_PRESSURE, pressure); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_WIND_SPEED, windSpeed); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_DEGREES, windDirection); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_MAX_TEMP, high); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_MIN_TEMP, low); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_SHORT_DESC, description); weatherValues.put(WeatherContract.WeatherEntry.COLUMN_WEATHER_ID, weatherId); cVVector.add(weatherValues); } // add to database if ( cVVector.size() > 0 ) { ContentValues[] cvArray = new ContentValues[cVVector.size()]; cVVector.toArray(cvArray); mContext.getContentResolver().bulkInsert(WeatherContract.WeatherEntry.CONTENT_URI,cvArray); } String sortOrder = WeatherContract.WeatherEntry.COLUMN_DATE + " ASC"; Uri weatherForLocationUri = WeatherContract.WeatherEntry.buildWeatherLocationWithStartDate( locationSetting, System.currentTimeMillis()); Cursor cur = mContext.getContentResolver().query(weatherForLocationUri, null, null, null, sortOrder); cVVector = new Vector<ContentValues>(cur.getCount()); if ( cur.moveToFirst() ) { do { ContentValues cv = new ContentValues(); DatabaseUtils.cursorRowToContentValues(cur, cv); cVVector.add(cv); } while (cur.moveToNext()); } Log.d(LOG_TAG, "FetchWeatherTask Complete. " + cVVector.size() + " Inserted"); } catch (JSONException e) { Log.e(LOG_TAG, e.getMessage(), e); e.printStackTrace(); } return null; } @Override protected Void doInBackground(String... params) { // If there's no zip code, there's nothing to look up. Verify size of params. if (params.length == 0) { return null; } String locationQuery = params[0]; // These two need to be declared outside the try/catch // so that they can be closed in the finally block. HttpURLConnection urlConnection = null; BufferedReader reader = null; // Will contain the raw JSON response as a string. String forecastJsonStr = null; String format = "json"; String units = "metric"; int numDays = 14; try { // Construct the URL for the OpenWeatherMap query // Possible parameters are avaiable at OWM's forecast API page, at // http://openweathermap.org/API#forecast final String FORECAST_BASE_URL = "http://api.openweathermap.org/data/2.5/forecast/daily?"; final String QUERY_PARAM = "q"; final String FORMAT_PARAM = "mode"; final String UNITS_PARAM = "units"; final String DAYS_PARAM = "cnt"; final String APPID_PARAM = "APPID"; Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon() .appendQueryParameter(QUERY_PARAM, params[0]) .appendQueryParameter(FORMAT_PARAM, format) .appendQueryParameter(UNITS_PARAM, units) .appendQueryParameter(DAYS_PARAM, Integer.toString(numDays)) .appendQueryParameter(APPID_PARAM,OPEN_WEATHER_MAP_API_KEY) .build(); URL url = new URL(builtUri.toString()); // Create the request to OpenWeatherMap, and open the connection urlConnection = (HttpURLConnection) url.openConnection(); urlConnection.setRequestMethod("GET"); urlConnection.connect(); // Read the input stream into a String InputStream inputStream = urlConnection.getInputStream(); StringBuffer buffer = new StringBuffer(); if (inputStream == null) { // Nothing to do. return null; } reader = new BufferedReader(new InputStreamReader(inputStream)); String line; while ((line = reader.readLine()) != null) { // Since it's JSON, adding a newline isn't necessary (it won't affect parsing) // But it does make debugging a *lot* easier if you print out the completed // buffer for debugging. buffer.append(line + "\n"); } if (buffer.length() == 0) { // Stream was empty. No point in parsing. return null; } forecastJsonStr = buffer.toString(); } catch (IOException e) { Log.e(LOG_TAG, "Error ", e); // If the code didn't successfully get the weather data, there's no point in attemping // to parse it. return null; } finally { if (urlConnection != null) { urlConnection.disconnect(); } if (reader != null) { try { reader.close(); } catch (final IOException e) { Log.e(LOG_TAG, "Error closing stream", e); } } } return null; } }
  • 2
    A lot of extra code. Fragment you have added, but the list is empty. Perhaps due to the fact that after completing the task of downloading data, you either do not enter it anywhere or add it to the adapter or notify the adapter of the arrival of new data. - YurySPb ♦

1 answer 1

  1. The FetchWeatherTask class FetchWeatherTask no onPostExecute method
  2. You make a request, but do not explicitly call for data parsing.
  3. In the onPostExecute method you will need to notify the fragment that you have written the data.

So what you did was get the string from the server and that's it.

  • no, the problem was not that. I don’t know what exactly, I’ll understand now. I copied them to FetchWeatherTask and put it in my own, it all worked. I didn’t add and miss that. The problem is solved. - Rost
  • FetchWeatherTask you will be exactly different;) - Chaynik
  • Well, there the problem was not in onPostExecute. - Rost