java - 重构asynctask线程

Question

这是尝试使用 Android 中的线程重建应用程序时出现的问题。仅在 1 行中标记错误

MainActivity.java

 package com.example.androidjppf.sunshine;
    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.support.v7.app.ActionBarActivity;
    import android.view.Menu;
    import android.view.MenuItem;



    public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction().add(R.id.container, new ForecastFragment())//<---Error line
                    .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.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;
        }

        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.

    //public static class PlaceholderFragment extends Fragment {

      //  public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);

            return rootView;
        }*/


    //}
 }

预测 fragment :

package com.example.androidjppf.sunshine;

import android.app.Fragment;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
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.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
* Created by g4-2380la on 21/01/2015.
*/
//@TargetApi(Build.VERSION_CODES.HONEYCOMB)
public class ForecastFragment extends Fragment {

public ForecastFragment(){

}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_main, container, false);

    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));

    //Now that we have some dummy forecast data. create an ArrayAdapter.
    //This will take data from the source (our dummy forecast)
    //Use it to populate the ListView it's attached to

    ArrayAdapter<String> mForecastAdapter = new ArrayAdapter<String>(
            //The current context (fragment´s parent activity)
            getActivity(),
            //ID of list item layout
            R.layout.list_item_forecast,
            //ID of the textview to populate
            R.id.list_item_forecast_textview,
            //Forecast data
            weekForecast);
    //Get a reference to ListView and attach this adapter to it
    ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast);
    listView.setAdapter(mForecastAdapter);

    return rootView;
}

public class FetchWeatherTask extends AsyncTask<Void, Void, Void> {

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

   @Override
    protected Void doInBackground(Void... Params) {

            // 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;

            try {
                // Construct the URL for the OpenWeatherMap query
                // Possible parameters are available at OWM's forecast API page, at
                // http://openweathermap.org/API#forecast
                URL url = new URL("http://api.openweathermap.org/data/2.5/forecast/daily?q=94043&mode=json&units=metric&cnt=7");

                // 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;
                    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.
                    //forecastJsonStr = null;
                    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 attempting
                // to parse it.
                forecastJsonStr = 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;
    }
}
}

这是输出:

Error:(19, 21) error: no suitable method found for add(int,ForecastFragment)
method FragmentTransaction.add(Fragment,String) is not applicable
(argument mismatch; int cannot be converted to Fragment)
method FragmentTransaction.add(int,Fragment) is not applicable
(argument mismatch; ForecastFragment cannot be converted to Fragment)

Answer 1

ForecastFragment 需要扩展支持 Fragment 类 ( android.support.v4.app.Fragment )，而不是常规 Fragment 类 ( android.app.Fragment )。