Question

我在Android应用程序开发上做了udacity课程。我已经为天气应用程序创建了一个刷新菜单按钮，但是当我点击刷新菜单时数据根本没有更新。这是代码（请忽略arrayadapter）

＆＃13;

package app.sunshine.android.example.com.sunshine;

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
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;

/**
* A placeholder fragment containing a simple view.
*/
public class ForecastFragment extends Fragment
{

public ForecastFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Add this line in order for this fragment to handle menu events.
    setHasOptionsMenu(true);
}

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    inflater.inflate(R.menu.forecastfragment, 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) {
        FetchWeatherTask weatherTask = new FetchWeatherTask();
        weatherTask.execute();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    String[] forecastArray = {
        "Today - Sunny - 88/63",
        "Tomarrow - Foggy - 70/40",
        "Wed - Sunny - 88/63",
        "Thurs - Sunny - 88/63",
        "Fri - Sunny - 88/63",
        "Sat - Sunny - 88/63",
        "Sun - Sunny - 88/63"};

List<String> weekForecast = new ArrayList<String>(Arrays.asList(forecastArray));
    ArrayAdapter<String> mForecastAdapter= new ArrayAdapter<String>(
            getActivity(),
            R.layout.list_item_forecast,
            R.id.list_item_forecast_textview,
            weekForecast
   );

    // 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;
    View rootView=inflater.inflate(R.layout.fragment_main, container, false);
    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 avaiable 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?id=1261481&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.
                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;
    }
}
}

＆＃13;

Answer 1

您在forecastJsonStr中以json的形式提取的数据。您没有在任何地方使用此获取的字符串。覆盖asynctask类的onPostExecute()方法，它将作为doInBackground()方法返回的参数接收。然后解析这个（forecastJsonStr）json字符串并在需要的地方设置值。我希望这有帮助

Answer 2

感谢您的帮助。我添加了这些行以使其正常工作

@Override
        protected void onPostExecute(String[] result) {
            if (result != null) {
                mForecastAdapter.clear();
                for(String dayForecastStr : result) {
                    mForecastAdapter.add(dayForecastStr);
                }
                // New data is back from the server.  Hooray!
            }
        }

刷新菜单不更新内容

2 个答案: