片段旋轉

Question

我有以下代碼，這些代碼從openweathermap API中檢索一些天氣數據。 AsyncTask類用於此目的。

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;
    }
}
}

我的問題是如何讓我的異步任務類在手機旋轉時正常工作。換句話說，我不想殺死我的Fragment，但存儲天氣就可以了。 我在這里也看到了其他問題，但是我對這部分感到困惑。 謝謝。

Answer 1

建議不要在清單中進行配置更改，以保存片段實例。

相反，您應該將片段的實例保存在容器活動的onSaveInstanceState（）重寫方法中。 以下是一個可以幫助您的小片段：

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

現在，在容器活動的onCreate方法中檢查bundle是否為null：

    if(savedInstanceState!=null){
            Fragment fragment = getSupportFragmentManager().getFragment(savedInstanceState,"fragmentInstanceSaved");
            //recreate your preserved fragment here
        }else{
            //goto ur default activity or fragment....
}