片段轮换

Question

我有以下代码从openweathermap api中检索一些天气数据。 AsyncTask类用于此目的。

public class ForecastFragment extends Fragment {
String imageUrl;
ListView listView;
List<WeatherForecastData> WeatherForecastDataList;
String IMG_URL = "http://api.openweathermap.org/img/w/";
Fragment fragment;

public ForecastFragment() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    //Inflate xml view and convert it to a View object
    View rootView = inflater.inflate(R.layout.fragment_forecast, container, false);

    //Initialise ListView.
    listView = (ListView) rootView.findViewById(R.id.listView);
    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            String temp = WeatherForecastDataList.get(position).getWeatherTemperature();

            Toast.makeText(getActivity(), temp + "° C"+" Have a nice day", Toast.LENGTH_SHORT).show();
        }
    });
    return rootView;
}

//Now we are ready for further processing
@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);

    setRetainInstance(true);
    if (savedInstanceState == null) {
        if(isOnline()) {
            requestData("http://api.openweathermap.org/data/2.5/forecast/daily?lat=50.09&lon=14.42&cnt=9&&units=metric&mode=json");
        }else{
            Toast.makeText(getActivity(),"There is no internet connection",Toast.LENGTH_SHORT).show();
        }
    }

}

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    savedInstanceState.putString("ImageURL", imageUrl);
    super.onSaveInstanceState(savedInstanceState);
}

//We create a MyTask object,and execute the async. thread with the specified url which is shown just above.
private void requestData(String uri) {
    MyTask task = new MyTask();
    task.execute(uri);
}

//AsyncTask that will do the asynchronous threading. It displays the weather's icon,description
//and temperature in the main thread via the OnPostExecute(...) method.
private class MyTask extends AsyncTask<String, String, List<WeatherForecastData>> {

    @Override
    protected void onPreExecute() {
        //Used to initialise Views such as Progress Bars which are not needed for this
        //project.
    }

    @Override
    protected List<WeatherForecastData> doInBackground(String... params) {
        //Read the url,specify the METHOD GET, and store it in content.
        String content = HttpManager.getData(params[0]);
        //JSON parsing of the openweather api's response. It is not hard,but I had to use the
        //debugger quite a lot to make sure that I deserialise the correct JSON values into Strings.
        WeatherForecastDataList = WeatherJSONParser.parseFeed(content);
        //Fetching the url image
        for (WeatherForecastData d : WeatherForecastDataList) {
            try {
                imageUrl = IMG_URL + d.getPhoto();
                InputStream in = (InputStream) new URL(imageUrl).getContent();
                Bitmap bitmap = BitmapFactory.decodeStream(in);
                //Is it deprecated?
                d.setBitmap(bitmap);
                in.close();
            } catch (Exception e) {
                e.printStackTrace();

            }
        }
        return WeatherForecastDataList;
    }

    //WeatherForecastData is the Object that contains all that instances we want to display.
    @Override
    protected void onPostExecute(List<WeatherForecastData> result) {

        if (result == null) {
            Toast.makeText(getActivity(), "There is some wrong,and data can not be displayed", Toast.LENGTH_LONG).show();
            return;
        }
        WeatherForecastDataList = result;
        //Display the ListView.
        WeatherAdapter adapter = new WeatherAdapter(getActivity(), R.layout.weather_row, WeatherForecastDataList);
        listView.setAdapter(adapter);
    }

}

protected boolean isOnline() {
    ConnectivityManager cm = (ConnectivityManager) getActivity().getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo netInfo = cm.getActiveNetworkInfo();
    if (netInfo != null && netInfo.isConnectedOrConnecting()) {
        return true;
    } else {
        return false;
    }
}
}

我的问题是如何让我的异步任务类在手机旋转时工作。换句话说，我不希望我的片段被杀死，但是存储天气得到了。我也在这里看到了其他问题，但我对此部分感到困惑。谢谢。

Answer 1

在清单中进行配置更改不是保存片段实例的推荐方法。

相反，您应该在容器活动的onSaveInstanceState（）重写方法中保存片段的实例。 以下是一个可以帮助您的小片段：

202 Accepted

现在，在容器活动的onCreate方法中检查bundle是否为null：

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    getSupportFragmentManager().putFragment(outState,"fragmentInstanceSaved",getSupportFragmentManager().findFragmentById(R.id.fragment_container));
}