Sunshine Project：刷新应用程序后数据没有更新？

Question

ForecastFragment.java

// Created by vgangwar7 on 31/05/16.
public class ForecastFragment extends Fragment {
public final class BuildConfig {
    public static final String OPEN_WEATHER_MAP_API_KEY = "1912b14c788b31e4f1ae441a0ceefb18";
}

private ArrayAdapter<String> forecastAdapter;
public ForecastFragment(){}

public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    // Add this line in order for this fragment to handle menu events
    setHasOptionsMenu(true);
    updateWeather();
}

public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    // Inflate the menu; this adds items to the action bar if it is present.
    inflater.inflate(R.menu.forecastfragment, menu);
}

public boolean onOptionsItemSelected(MenuItem menuItem) {
    int id = menuItem.getItemId();

    if (id == R.id.action_refresh) {
        FetchWeatherTask weatherTask = new FetchWeatherTask();
        weatherTask.execute("110085");
        return true;
    }

    return super.onOptionsItemSelected(menuItem);
}

private void updateWeather() {
    FetchWeatherTask weatherTask = new FetchWeatherTask();
    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity());
    String location = preferences.getString(getString(R.string.pref_location_key),
            getString(R.string.pref_location_default));
    weatherTask.execute(location);
}

public void onStart() {
    super.onStart();
    updateWeather();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    String[] forecastArray =
            {"Today - Sunny - 88/63",
            "Tomorrow - Foggy - 70/40",
            "Weds - Cloudy - 72/63",
            "Thurs - Asteroids - 75/65",
            "Fri - Heavy Rain - 65/56",
            "Sat - HELP TRAPPED IN WEATHERSITUATION - 65/51",
            "Sun - Sunny - 88/68"};

    List<String> weekForecast = new ArrayList<String>(Arrays.asList(forecastArray));

    forecastAdapter = new ArrayAdapter<>(getActivity(),R.layout.list_item_forecast, R.id.list_item_forecast_textview, weekForecast);
    View rootView = inflater.inflate(R.layout.fragment_main, container, false);
    ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast);
    listView.setAdapter(forecastAdapter);
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
            Toast.makeText(getActivity(), forecastAdapter.getItem(position), Toast.LENGTH_SHORT).show();
        }
    });
    return rootView;
}

public class FetchWeatherTask extends AsyncTask<String, Void, String[]> {

    private final String TAG = FetchWeatherTask.class.getSimpleName();

    String format = "json";
    String units = "metric";
    final int numDays = 7;

    private String getReadableDateString(long time) {
        // Because the API returns a unix timestamp (measured in seconds),
        // it must be converted to milliseconds in order to be converted to valid date.
        SimpleDateFormat shortenedDateFormat = new SimpleDateFormat("EEE MMM dd");
        return shortenedDateFormat.format(time);
    }
    /**
     * Take the String representing the complete forecast in JSON Format and
     * pull out the data we need to construct the Strings needed for the wireframes.
     *
     * Fortunately parsing is easy:  constructor takes the JSON string and converts it
     * into an Object hierarchy for us.
     */
    //Prepare the weather high/lows for presentation.
    private String formatHighLows(double high, double low) {
        // For presentation, assume the user doesn't care about tenths of a degree.
        long roundedHigh = Math.round(high);
        long roundedLow = Math.round(low);

        String highLowStr = roundedHigh + "/" + roundedLow;
        return highLowStr;
    }

    /**
     * Take the String representing the complete forecast in JSON Format and
     * pull out the data we need to construct the Strings needed for the wireframes.
     *
     * Fortunately parsing is easy:  constructor takes the JSON string and converts it
     * into an Object hierarchy for us.
     */
    private String[] getWeatherDataFromJson(String forecastJsonStr, int numDays)
            throws JSONException {

        // These are the names of the JSON objects that need to be extracted.
        final String OWM_LIST = "list";
        final String OWM_WEATHER = "weather";
        final String OWM_TEMPERATURE = "temp";
        final String OWM_MAX = "max";
        final String OWM_MIN = "min";
        final String OWM_DESCRIPTION = "main";

        JSONObject forecastJson = new JSONObject(forecastJsonStr);
        JSONArray weatherArray = forecastJson.getJSONArray(OWM_LIST);


        String[] resultStrs = new String[numDays];
        for(int i = 0; i < weatherArray.length(); i++) {
            // For now, using the format "Day, description, hi/low"
            String day;
            String description;
            String highAndLow;

            // Get the JSON object representing the day
            JSONObject dayForecast = weatherArray.getJSONObject(i);

            //create a Gregorian Calendar, which is in current date
            GregorianCalendar gc = new GregorianCalendar();
            //add i dates to current date of calendar
            gc.add(GregorianCalendar.DATE, i);
            //get that date, format it, and "save" it on variable day
            Date time = gc.getTime();
            SimpleDateFormat shortenedDateFormat = new SimpleDateFormat("EEE MMM dd");
            day = shortenedDateFormat.format(time);

            // description is in a child array called "weather", which is 1 element long.
            JSONObject weatherObject = dayForecast.getJSONArray(OWM_WEATHER).getJSONObject(0);
            description = weatherObject.getString(OWM_DESCRIPTION);

            // 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);
            double high = temperatureObject.getDouble(OWM_MAX);
            double low = temperatureObject.getDouble(OWM_MIN);

            highAndLow = formatHighLows(high, low);
            resultStrs[i] = day + " - " + description + " - " + highAndLow;
        }

        for (String s : resultStrs) {
            Log.v("FetchWeatherTask", "Forecast entry: " + s);
        }
        return resultStrs;

    }

    @Override
    protected String[] doInBackground(String... params) {

        if (params.length == 0) {
            return null;
        }

        //These two needed to be declared outside try catch block
        HttpURLConnection urlConnection = null;
        BufferedReader reader = null;

        String forecastJsonStr = null;

            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, BuildConfig.OPEN_WEATHER_MAP_API_KEY)
                        .build();

                URL url = new URL(builtUri.toString());

                Log.v(TAG, "Built URI " + builtUri.toString());

                // Create the request to OpenWeatherMap, and open the connection
                urlConnection = (HttpURLConnection) url.openConnection();

                // 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("ForecastFragment", "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("ForecastFragment", "Error closing stream", e);
                    }
                }
            }
        try{
            getWeatherDataFromJson(forecastJsonStr, numDays);
        }catch (JSONException e){
            Log.e(TAG ,e.getMessage(), e);
            e.printStackTrace();
        }

        return null;

    }

    @Override
    public void onPostExecute(String[] result) {
        if (result != null) {
            forecastAdapter.clear();
            for (String dayForecastStr : result) {
                forecastAdapter.addAll(dayForecastStr);
            }
            forecastAdapter.notifyDataSetChanged();
        }
    }

}
}

MainActivity.java

 public class MainActivity extends AppCompatActivity 
 {

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (savedInstanceState == null) {


     getSupportFragmentManager().beginTransaction().add(R.id.container, new ForecastFragment()).commit();
    }

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);

    return true;
}

@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();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }
    if (id == R.id.action_refresh) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}
}

Though, In my logcat , I am able to see the fetched data from the API and there isn't any error in the code. LogCat -

06-04 16:11:31.432 3730-3769/com.example.vgangwar7.sunshine V/FetchWeatherTask: Forecast entry: Sun Jun 05 - Clear - 43/31 06-04 16:11:31.432 3730-3769/com.example.vgangwar7.sunshine V/FetchWeatherTask: Forecast entry: Mon Jun 06 - Clear - 40/26 06-04 16:11:31.432 3730-3769/com.example.vgangwar7.sunshine V/FetchWeatherTask: Forecast entry: Tue Jun 07 - Clear - 39/28 06-04 16:11:31.432 3730-3769/com.example.vgangwar7.sunshine V/FetchWeatherTask: Forecast entry: Wed Jun 08 - Clear - 39/26 06-04 16:11:31.432 3730-3769/com.example.vgangwar7.sunshine V/FetchWeatherTask: Forecast entry: Thu Jun 09 - Clear - 41/27 06-04 16:11:31.432 3730-3769/com.example.vgangwar7.sunshine V/FetchWeatherTask: Forecast entry: Fri Jun 10 - Rain - 39/26

Answer 1

try Override onStart method:

@Override
public void onStart(){
    super.onStart();
    updateWeather();
}

Regards.

Answer 2

When you perform async task, you need to make sure the task is completed before using the result retruned by the task. In your case, when refresh is selected, you are executing task with weatherTask.execute("110085"); . Lets say it takes 3 sec to complete the task and return the result. but your return statement in next line will be executed immediately forcing the layout to reload ( lets say it takes 1 sec here for reloading). What happens here is when you perform async task, another process will be created to fetch data and original execution continues immediately without waiting for the async task to complete.ie the execution moves to next line immediately without waiting for result from your task. In your case , reloading is done before your task actually pulled the data. As per example, your screen loads in first second of entering the optionSelected method, but only after 2 more seconds, you are getting weather data from the async task. So the updated data appears in logcat , but not in screen as the activity did not receive the data while it was loading. So you need to makes sure you load your layout only after you receive your data . you can do this by calling get() on your execute.

In method onOptionsItemSelected of ForecastFragment , change

weatherTask.execute("110085");

to

weatherTask.execute("110085").get() ;

This should do the magic for you.

Answer 3

I'm not sure about when you want to "refresh" the data and how are you doing it, can you explain only your strategy to update the data instead of copying all your code? Normally the steps are:

1. perform http request in other thread
2. once the request is ready pass the response to the main thread
3. in the main thread update the UI with the data (this depends on the controls you are using in your app to show the data.

I imagine you have read about the activity states in Android. If you didn't, do it. Then you will be able to use onStart or onResume depending on your needs.

Answer 4

Call the updateWeather(); function in the OnOptionsItemSelected() method

public boolean onOptionsItemSelected(MenuItem menuItem) {
int id = menuItem.getItemId();

   if (id == R.id.action_refresh) {
        //FetchWeatherTask weatherTask = new FetchWeatherTask();
        //weatherTask.execute("110085");
        updateWeather();
        return true;
    }

    return super.onOptionsItemSelected(menuItem);
}

In your doInBackground add a return statement when you make the weather forecast strings from the forecastJsonStr

@Override
protected String[] doInBackground(String... params) {
    .//your code
    .//your code
    .//your code
    .
    .
    try{
        return getWeatherDataFromJson(forecastJsonStr, numDays);//add return here!!
    }catch (JSONException e){
        Log.e(TAG ,e.getMessage(), e);
        e.printStackTrace();
    }

    return null;
}