SharedPreferences在更改时不启动onStart

Question

我已经编写了一个应用程序来获取来自USGS的地震数据，我想为想要使用不同mag等级检查的用户添加首选项更改。但是，如果首选项发生更改，onStart不会触发。请建议我如何修改代码

public class EarthquakeFragment extends Fragment{ 
public EarthquakeFragment(){ 
} 

ListView listView; 
private EarthquakeAdapter eAdapter; 

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

    eAdapter = new EarthquakeAdapter(getActivity(), new ArrayList<EarthquakeInfo>()); 
    listView = (ListView) rootView.findViewById(R.id.list); 
    listView.setAdapter(eAdapter); 

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
      EarthquakeInfo currentEarthquake = eAdapter.getItem(position); 
      String url = currentEarthquake.getUrl(); 

      Intent intent = new Intent(Intent.ACTION_VIEW); 
      intent.setData(Uri.parse(url)); 
      startActivity(intent); 
     } 
    }); 
    setHasOptionsMenu(true); 
    // Start the AsyncTask to fetch the earthquake data 
    EarthquakeAsyncTask task = new EarthquakeAsyncTask(); 
    task.execute(); 
    return rootView; 
} 


/** 
* {@link AsyncTask} to perform the network request on a background thread, and then 
* update the UI with the list of earthquakes in the response. 
* 
* AsyncTask has three generic parameters: the input type, a type used for progress updates, and 
* an output type. Our task will take a String URL, and return an Earthquake. We won't do 
* progress updates, so the second generic is just Void. 
* 
* We'll only override two of the methods of AsyncTask: doInBackground() and onPostExecute(). 
* The doInBackground() method runs on a background thread, so it can run long-running code 
* (like network activity), without interfering with the responsiveness of the app. 
* Then onPostExecute() is passed the result of doInBackground() method, but runs on the 
* UI thread, so it can use the produced data to update the UI. 
*/ 
private class EarthquakeAsyncTask extends AsyncTask<String, Void, List<EarthquakeInfo>> { 

    /** 
    * This method runs on a background thread and performs the network request. 
    * We should not update the UI from a background thread, so we return a list of 
    * {@link EarthquakeInfo}s as the result. 
    */ 
    @Override 
    protected List<EarthquakeInfo> doInBackground(String... urls) { 


     SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity()); 
     String maglevel = preferences.getString(getString(R.string.pref_mag_key), ""); 

      final String BASE_URL= "http://earthquake.usgs.gov/fdsnws/event/1/query?"; 
      final String FORMAT_PARAM = "format"; 
      final String ORDER_PARAM = "orderby"; 
      final String START_PARAM = "starttime"; 
      final String END_PARAM = "endtime"; 
      final String MINMAG_PARAM = "minmag"; 
      String format = "geojson"; 
      String order = "time"; 
      String start = "2016-01-01"; 
      String end = "2016-07-28"; 
      String minmag = maglevel; 

      Uri buildUri = Uri.parse(BASE_URL).buildUpon() 
        .appendQueryParameter(FORMAT_PARAM, format) 
        .appendQueryParameter(ORDER_PARAM, order) 
        .appendQueryParameter(START_PARAM, start) 
        .appendQueryParameter(END_PARAM, end) 
        .appendQueryParameter(MINMAG_PARAM, minmag) 
        .build(); 
      String url = buildUri.toString(); 


     // Don't perform the request if there are no URLs, or the first URL is null. 
     if (url == null) { 
      return null; 
     } 

     List<EarthquakeInfo> result = QueryUtils.fetchEarthquakeData(url); 
     return result; 
    } 

    /** 
    * This method runs on the main UI thread after the background work has been 
    * completed. This method receives as input, the return value from the doInBackground() 
    * method. First we clear out the adapter, to get rid of earthquake data from a previous 
    * query to USGS. Then we update the adapter with the new list of earthquakes, 
    * which will trigger the ListView to re-populate its list items. 
    */ 
    @Override 
    protected void onPostExecute(List<EarthquakeInfo> data) { 
     // Clear the adapter of previous earthquake data 
     onStart(); 
     eAdapter.clear(); 

     // If there is a valid list of {@link Earthquake}s, then add them to the adapter's 
     // data set. This will trigger the ListView to update. 
     if (data != null && !data.isEmpty()) { 
      eAdapter.addAll(data); 
     } 
    } 
} 
} 

非常感谢!!!!!

Answer 1

聆听SharedPreferences上的更改不会如此。

对于您需要实现SharedPreferences.OnSharedPreferenceChangeListener

SharedPreferences.OnSharedPreferenceChangeListener spChanged = new 
          SharedPreferences.OnSharedPreferenceChangeListener() { 
      @Override 
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, 
      String key) { 
     // your stuff here 
    } 
}; 

在你PreferenceActivity，即让你的PreferenceActivity类的成员，然后做registerOnSharedPreferenceChangeListener(spChanged)在PreferenceActivity.onCreate()方法。

Answer 2

我终于解决了这个问题。

我在onResume上调用fetch数据方法。由于我无法在AsyncTask上使用空数据获取数据，因此会导致NullPointExection。所以我让我执行AsyncTask的默认网址。之后，我在onResume上添加SharePreference。之后，问题就解决了。

这是我的代码。

public class EarthquakeFragment extends Fragment{ 

public EarthquakeFragment(){ 
} 

ListView listView; 
EarthquakeAdapter eAdapter; 

@Override 
public View onCreateView (LayoutInflater inflater, ViewGroup container, Bundle saveInstanceState) 
{ 
    String defaultUrl = getActivity().getString(R.string.default_link); 

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

    eAdapter = new EarthquakeAdapter(getActivity(), new ArrayList<EarthquakeInfo>()); 
    listView = (ListView) rootView.findViewById(R.id.list); 
    listView.setAdapter(eAdapter); 

    listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
      EarthquakeInfo currentEarthquake = eAdapter.getItem(position); 
      String url = currentEarthquake.getUrl(); 

      Intent intent = new Intent(Intent.ACTION_VIEW); 
      intent.setData(Uri.parse(url)); 
      startActivity(intent); 
     } 
    }); 
    setHasOptionsMenu(true); 
    // Start the AsyncTask to fetch the earthquake data 
    EarthquakeAsyncTask task = new EarthquakeAsyncTask(); 
    task.execute(defaultUrl); 
    return rootView; 
} 

private void updateEarthquake() { 
    EarthquakeAsyncTask earthquakeTask = new EarthquakeAsyncTask(); 
    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity()); 
    String maglevel = preferences.getString(getString(R.string.pref_mag_key), getString(R.string.pref_mag_6)); 
    String startTime = preferences.getString(getString(R.string.start_key), getString(R.string.pref_time_2016)); 
    String sortby= preferences.getString(getString(R.string.sort_key), getString(R.string.pref_sortby_time)); 

    final String BASE_URL= "http://earthquake.usgs.gov/fdsnws/event/1/query?"; 
    final String FORMAT_PARAM = "format"; 
    final String ORDER_PARAM = "orderby"; 
    final String START_PARAM = "starttime"; 
    final String END_PARAM = "endtime"; 
    final String MINMAG_PARAM = "minmag"; 
    final String LIMIT_PARAM = "limit"; 
    final String format = "geojson"; 
    final String order = sortby; 
    String start = startTime+"-01-01"; 
    String end = startTime+"-12-31"; 
    String minmag = maglevel; 
    final String limit = "10"; 

    Uri buildUri = Uri.parse(BASE_URL).buildUpon() 
      .appendQueryParameter(FORMAT_PARAM, format) 
      .appendQueryParameter(ORDER_PARAM, order) 
      .appendQueryParameter(START_PARAM, start) 
      .appendQueryParameter(END_PARAM, end) 
      .appendQueryParameter(MINMAG_PARAM, minmag) 
      .appendQueryParameter(LIMIT_PARAM, limit) 
      .build(); 
    String url = buildUri.toString(); 

    // Don't perform the request if there are no URLs, or the first URL is null. 
    if (url == null) { 
    } 
    earthquakeTask.execute(url); 
} 

@Override 
public void onResume(){ 
    super.onResume(); 
    updateEarthquake(); 
} 

/** 
* {@link AsyncTask} to perform the network request on a background thread, and then 
* update the UI with the list of earthquakes in the response. 
* 
* AsyncTask has three generic parameters: the input type, a type used for progress updates, and 
* an output type. Our task will take a String URL, and return an Earthquake. We won't do 
* progress updates, so the second generic is just Void. 
* 
* We'll only override two of the methods of AsyncTask: doInBackground() and onPostExecute(). 
* The doInBackground() method runs on a background thread, so it can run long-running code 
* (like network activity), without interfering with the responsiveness of the app. 
* Then onPostExecute() is passed the result of doInBackground() method, but runs on the 
* UI thread, so it can use the produced data to update the UI. 
*/ 
private class EarthquakeAsyncTask extends AsyncTask<String, Void, List<EarthquakeInfo>> { 

    /** 
    * This method runs on a background thread and performs the network request. 
    * We should not update the UI from a background thread, so we return a list of 
    * {@link EarthquakeInfo}s as the result. 
    */ 
    @Override 
    protected List<EarthquakeInfo> doInBackground(String... urls) { 

     List<EarthquakeInfo> result = QueryUtils.fetchEarthquakeData(urls[0]); 
     return result; 
    } 

    /** 
    * This method runs on the main UI thread after the background work has been 
    * completed. This method receives as input, the return value from the doInBackground() 
    * method. First we clear out the adapter, to get rid of earthquake data from a previous 
    * query to USGS. Then we update the adapter with the new list of earthquakes, 
    * which will trigger the ListView to re-populate its list items. 
    */ 
    @Override 
    protected void onPostExecute(List<EarthquakeInfo> data) { 
     // Clear the adapter of previous earthquake data 
     eAdapter.clear(); 
     // If there is a valid list of {@link Earthquake}s, then add them to the adapter's 
     // data set. This will trigger the ListView to update. 
     if (data != null && !data.isEmpty()) { 
      eAdapter.addAll(data); 
     } 
    } 
} 
} 

这是我的设置活动代码

public class SettingActivity extends PreferenceActivity 
    implements Preference.OnPreferenceChangeListener{ 

@Override 
public void onCreate (Bundle savedInstanceState){ 
    super.onCreate(savedInstanceState); 
    addPreferencesFromResource(R.xml.pref_general); 

    bindPreferenceSummaryToValue(findPreference(getString(R.string.pref_mag_key))); 
    bindPreferenceSummaryToValue(findPreference(getString(R.string.start_key))); 
    bindPreferenceSummaryToValue(findPreference(getString(R.string.sort_key))); 

} 

private void bindPreferenceSummaryToValue(Preference preference) { 
    preference.setOnPreferenceChangeListener(this); 
    onPreferenceChange(preference, 
      PreferenceManager 
        .getDefaultSharedPreferences(preference.getContext()) 
        .getString(preference.getKey(), "")); 

} 

@Override 
public boolean onPreferenceChange(Preference preference, Object newValue) { 
    String stringValue = newValue.toString(); 
    if (preference instanceof ListPreference) { 
     ListPreference preferences = (ListPreference) preference; 
     int prefIndex = preferences.findIndexOfValue(stringValue); 
     if (prefIndex >= 0) { 
      preference.setSummary(preferences.getEntries()[prefIndex]); 
     }else { 
      preference.setSummary(stringValue); 
     } 
    } 
    return true; 
} 
} 

希望它可以帮助谁也面临同样问题的任何人。请同时告知是否有任何“错误理由”在onResume中获取数据。

谢谢你的回复!!!!!!