使用公共类的“无法解析符号”错误

Question

I have 1 activity and 1 fragment involved on this one. In the fragment I declare the public class FetchWeatherTask:

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

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

        @Override
        protected void onPostExecute(String[] result) {
            if (result != null){
                mForecastAdapter.clear();
                for(String dayForecastStr : result)
                    mForecastAdapter.add(dayForecastStr);
            }
        }





        //region JSON PARSING SNIPPET
        //*****************************************************************************************************************************


        /* The date/time conversion code is going to be moved outside the asynctask later,
 * so for convenience we're breaking it out into its own method now.
 */
        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);
        }

        /**
         * Prepare the weather high/lows for presentation.
         */
        private String formatHighLows(double high, double low) {


            String unitType = prefs.getString(
                    getString(R.string.pref_default_unit_key),
                    getString(R.string.pref_default_temp));






            // 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);

            // 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();

            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);

                // The date/time is returned as a long.  We need to convert that
                // into something human-readable, since most people won't read "1400356800" as
                // "this saturday".
                long dateTime;
                // Cheating to convert this to UTC time, which is what we want anyhow
                dateTime = dayTime.setJulianDay(julianStartDay+i);
                day = getReadableDateString(dateTime);

                // 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(LOG_TAG, "Forecast Entry: " + s);
            }
            return resultStrs;
        }


        //endregion


        @Override
        protected String[] doInBackground(String... params) {
            if(params.length == 0)
                return null;

            //region HTTPConnection Snippet
            // **********************************************************************************************************************************************************************************


            // 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 = 7;
            String apiKey ="b1b15e88fa797225412429c1c50c122a";



            try {

                // Construct the URL for the OpenWeatherMap query
                // Possible parameters are avaiable at OWM's forecast API page, at
                // http://openweathermap.org/API#forecast

                //region URI_BUILDER
                //***********************************************************************************************************************
                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 API_KEY_PARAM="appid";

                Uri buildUri = 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(API_KEY_PARAM,apiKey).build();

                //Log.v(LOG_TAG, "BuiltURI: " + buildUri.toString());

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

                //endregion



                // 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.
                    forecastJsonStr = 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.
                    forecastJsonStr = null;
                }
                forecastJsonStr = buffer.toString();

                //(LOG_TAG, "Forecast JSON String: " + forecastJsonStr);


            } catch (IOException e) {
                Log.e("PlaceholderFragment", "Error ", e);
                // If the code didn't successfully get the weather data, there's no point in attemping
                // to parse it.
                forecastJsonStr = null;
            } finally{
                if (urlConnection != null) {
                    urlConnection.disconnect();
                }
                if (reader != null) {
                    try {
                        reader.close();
                    } catch (final IOException e) {
                        Log.e("PlaceholderFragment", "Error closing stream", e);
                    }
                }
            }
            //endregion

            try{
                return getWeatherDataFromJson(forecastJsonStr,numDays);
            }
            catch (JSONException e){
                Log.e(LOG_TAG, e.getMessage(), e);
                e.printStackTrace();
            }




            return null;
        }


    }

This class is then instanciated in the MainActivity in the method onOptionsItemSelected:

@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) {

        startActivity(new Intent(this, SettingsActivity.class));
        return true;
    }
    if (id == R.id.action_refresh) {

        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
        String location = prefs.getString(getString(R.string.pref_location_key),
                getString(R.string.pref_default_location));


        FetchWeatherTask weatherTask = new FetchWeatherTask();
        weatherTask.execute(location);
        return true;
    }

    return super.onOptionsItemSelected(item);
}

}

The IDE suggest a change in the declaration of the weatherTaks by making it static. This does resolve the error on this method, although I am not able to use some other methods like:

String unitType = prefs.getString(

getString(R.string.pref_units_key), getString(R.string.pref_units_metric));

the inner getString will say "cannot use non-static methods on static methods" (i dont record the exact words but it was what it meant)

Resuming to the main objective: How can I use the public class in another activity, even though it's marked public and I even imported my package which is:

import com.example.diomonogatarilaptop.sunshine.MainActivityFragment;

Thank you for reading

EDIT: Fragment code

package com.example.diomonogatarilaptop.sunshine;

import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.support.v4.app.Fragment;
import android.text.format.Time;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.text.SimpleDateFormat;
import java.util.ArrayList;


public class MainActivityFragment extends Fragment {



    public final SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getActivity());
    public static ArrayAdapter<String> mForecastAdapter;

    public MainActivityFragment() {

    }


    private void updateWeather(){
        FetchWeatherTask weatherTask = new FetchWeatherTask();
        String location = prefs.getString(getString(R.string.pref_location_key),
                        getString(R.string.pref_default_location));
        weatherTask.execute(location);
    }
    @Override
    public void onStart(){
        super.onStart();
        updateWeather();
    }


    //region AsyncTask Weather Fetcher
    //********************************************************************************************************************************************************************************************
    public class FetchWeatherTask extends AsyncTask<String,Void,String[]>{

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

        @Override
        protected void onPostExecute(String[] result) {
            if (result != null){
                mForecastAdapter.clear();
                for(String dayForecastStr : result)
                    mForecastAdapter.add(dayForecastStr);
            }
        }





        //region JSON PARSING SNIPPET
        //*****************************************************************************************************************************


        /* The date/time conversion code is going to be moved outside the asynctask later,
 * so for convenience we're breaking it out into its own method now.
 */
        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);
        }

        /**
         * Prepare the weather high/lows for presentation.
         */
        private String formatHighLows(double high, double low) {


            String unitType = prefs.getString(
                    getString(R.string.pref_default_unit_key),
                    getString(R.string.pref_default_temp));






            // 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);

            // 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();

            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);

                // The date/time is returned as a long.  We need to convert that
                // into something human-readable, since most people won't read "1400356800" as
                // "this saturday".
                long dateTime;
                // Cheating to convert this to UTC time, which is what we want anyhow
                dateTime = dayTime.setJulianDay(julianStartDay+i);
                day = getReadableDateString(dateTime);

                // 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(LOG_TAG, "Forecast Entry: " + s);
            }
            return resultStrs;
        }


        //endregion


        @Override
        protected String[] doInBackground(String... params) {
            if(params.length == 0)
                return null;

            //region HTTPConnection Snippet
            // **********************************************************************************************************************************************************************************


            // 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 = 7;
            String apiKey ="b1b15e88fa797225412429c1c50c122a";



            try {

                // Construct the URL for the OpenWeatherMap query
                // Possible parameters are avaiable at OWM's forecast API page, at
                // http://openweathermap.org/API#forecast

                //region URI_BUILDER
                //***********************************************************************************************************************
                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 API_KEY_PARAM="appid";

                Uri buildUri = 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(API_KEY_PARAM,apiKey).build();

                //Log.v(LOG_TAG, "BuiltURI: " + buildUri.toString());

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

                //endregion



                // 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.
                    forecastJsonStr = 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.
                    forecastJsonStr = null;
                }
                forecastJsonStr = buffer.toString();

                //(LOG_TAG, "Forecast JSON String: " + forecastJsonStr);


            } catch (IOException e) {
                Log.e("PlaceholderFragment", "Error ", e);
                // If the code didn't successfully get the weather data, there's no point in attemping
                // to parse it.
                forecastJsonStr = null;
            } finally{
                if (urlConnection != null) {
                    urlConnection.disconnect();
                }
                if (reader != null) {
                    try {
                        reader.close();
                    } catch (final IOException e) {
                        Log.e("PlaceholderFragment", "Error closing stream", e);
                    }
                }
            }
            //endregion

            try{
                return getWeatherDataFromJson(forecastJsonStr,numDays);
            }
            catch (JSONException e){
                Log.e(LOG_TAG, e.getMessage(), e);
                e.printStackTrace();
            }




            return null;
        }


    }
    //endregion
    //region onCreateView
    //***********************************************************************************************************************************
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {


        View rootView = inflater.inflate(R.layout.fragment, container, false);



        //region Where the data is







        mForecastAdapter = new ArrayAdapter<String>(
                getActivity(),
                R.layout.list_item_forecast,
                R.id.list_item_forecast_textview,
                new ArrayList<String>());

        ListView lista = (ListView)rootView.findViewById(R.id.listview_forecast);
        lista.setAdapter(mForecastAdapter);


        //region onClickListener manda tostas
        lista.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                String forecast = mForecastAdapter.getItem(position);
                Intent intent = new Intent(getContext(), DetailActivity.class)
                        .putExtra(Intent.EXTRA_TEXT, forecast);

                startActivity(intent);
            }
        });
        //endregion
        //endregion





















        return rootView;




    }
    //endregion






}

Answer 1

It's because you are trying to instantiate an inner class without a reference to an instance to the outer class. You should do,

new MainFragment(). new FetchWeatherTask();

But probably you already created an instance of MainFragment(let's say its mainFragment) then you should just use this:

mainFragment. new FetchWeatherTask();