AsyncTask 中的 getDefaultSharedPreferences(getActivity())
Posted
技术标签:
【中文标题】AsyncTask 中的 getDefaultSharedPreferences(getActivity())【英文标题】：getDefaultSharedPreferences(getActivity()) in AsyncTask 【发布时间】：2017-01-24 04:42:02 【问题描述】：public class MainActivityFragment extends Fragment
public static ArrayAdapter<String> mForecastAdapter;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
mForecastAdapter = new ArrayAdapter<String>(getActivity(), R.layout.list_item_forecast, R.id.list_item_forecast_textview, new ArrayList<String>());
ListView listview = (ListView) rootView.findViewById(R.id.listview_forecast);
listview.setAdapter(mForecastAdapter);
listview.setOnItemClickListener(new AdapterView.OnItemClickListener()
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long l)
String Forecast = mForecastAdapter.getItem(position);
Intent intent = new Intent(getActivity(), DetailActivity.class).putExtra(Intent.EXTRA_TEXT, Forecast);
startActivity(intent);
);
return rootView;
public class FetchWeatherTask extends AsyncTask<String, Void, String[]>
Context mContext;
private void FetchWeatherTask(Context context)
mContext = context;
private final String LOG_TAG = FetchWeatherTask.class.getSimpleName();
public String formatHighLows(double high, double low)
SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(mContext);
String unitType = sharedPrefs.getString(getString(R.string.pref_location_key),getString(R.string.pref_location_default));
/*
if(unitType.equals(getString(R.string.pref_units_imperial)))
high = (high*1.8) + 32;
low = (low * 1.8) +32;
else if (!unitType.equals(getString(R.string.pref_units_metric)))
*/
// For presentation, assume the user doesn't care about tenths of a degree.
long roundedHigh = Math.round(high);
long roundedLow = Math.round(low);
String highLowStr = roundedHigh + "/" + roundedLow;
return highLowStr;
/* The date/time conversion code is going to be moved outside the asynctask later,
* so for convenience we're breaking it out into its own method now.
*/
private String getReadableDateString(long time)
// Because the API returns a unix timestamp (measured in seconds),
// it must be converted to milliseconds in order to be converted to valid date.
Date date = new Date(time * 1000);
SimpleDateFormat format = new SimpleDateFormat("E, MMM d");
return format.format(date).toString();
/**
* Prepare the weather high/lows for presentation.
*/
/**
* Take the String representing the complete forecast in JSON Format and
* pull out the data we need to construct the Strings needed for the wireframes.
*
* Fortunately parsing is easy: constructor takes the JSON string and converts it
* into an Object hierarchy for us.
*/
private String[] getWeatherDataFromJson(String forecastJsonStr, int numDays)
throws JSONException
// These are the names of the JSON objects that need to be extracted.
final String OWM_LIST = "list";
final String OWM_WEATHER = "weather";
final String OWM_TEMPERATURE = "temp";
final String OWM_MAX = "max";
final String OWM_MIN = "min";
final String OWM_DATETIME = "dt";
final String OWM_DESCRIPTION = "main";
JSONObject forecastJson = new JSONObject(forecastJsonStr);
JSONArray weatherArray = forecastJson.getJSONArray(OWM_LIST);
String[] resultStrs = new String[numDays];
for(int i = 0; i < weatherArray.length(); i++)
// For now, using the format "Day, description, hi/low"
String day;
String description;
String highAndLow;
// Get the JSON object representing the day
JSONObject dayForecast = weatherArray.getJSONObject(i);
// The date/time is returned as a long. We need to convert that
// into something human-readable, since most people won't read "1400356800" as
// "this saturday".
long dateTime = dayForecast.getLong(OWM_DATETIME);
day = getReadableDateString(dateTime);
// description is in a child array called "weather", which is 1 element long.
JSONObject weatherObject = dayForecast.getJSONArray(OWM_WEATHER).getJSONObject(0);
description = weatherObject.getString(OWM_DESCRIPTION);
// Temperatures are in a child object called "temp". Try not to name variables
// "temp" when working with temperature. It confuses everybody.
JSONObject temperatureObject = dayForecast.getJSONObject(OWM_TEMPERATURE);
double high = temperatureObject.getDouble(OWM_MAX);
double low = temperatureObject.getDouble(OWM_MIN);
highAndLow = formatHighLows(high, low);
resultStrs[i] = day + " - " + description + " - " + highAndLow;
/*
for (String s : resultStrs)
Log.v(LOG_TAG,"Forecast entry: "+s);
*/
return resultStrs;
@Override
protected String[] doInBackground(String... 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;
String format = "json";
String units = "metric";
int numDays = 7;
String ApiKey = "8f044afff5747f43d54f5229904c5dbb";
try
// Construct the URL for the OpenWeatherMap query
// Possible parameters are avaiable at OWM's forecast API page, at
// http://openweathermap.org/API#forecast
final String FORECAST_BASE_URL = "http://api.openweathermap.org/data/2.5/forecast/daily?";
final String QUERY_PARM = "q";
final String FORMAT_PARM = "mode";
final String UNITS_PARM = "units";
final String DAYS_PARM = "cnt";
final String KEY_PARM = "appid";
Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon()
.appendQueryParameter(QUERY_PARM,params[0])
.appendQueryParameter(FORMAT_PARM,format)
.appendQueryParameter(UNITS_PARM,units)
.appendQueryParameter(DAYS_PARM,Integer.toString(numDays))
.appendQueryParameter(KEY_PARM,ApiKey).build();
URL url = new URL(builtUri.toString());
// 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;
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;
forecastJsonStr = buffer.toString();
// Log.v(LOG_TAG,"Forecast JSON String"+forecastJsonStr);
catch (IOException e)
Log.e("PlaceholderFragment", "Error ", e);
// If the code didn't successfully get the weather data, there's no point in attemping
// to parse it.
forecastJsonStr = null;
finally
if (urlConnection != null)
urlConnection.disconnect();
if (reader != null)
try
reader.close();
catch (final IOException e)
Log.e("PlaceholderFragment", "Error closing stream", e);
try
String[] FinalValue = getWeatherDataFromJson(forecastJsonStr,numDays);
for (String s : FinalValue)
Log.v(LOG_TAG,"Forecast entry: "+s);
return FinalValue;
catch (JSONException e)
Log.e(LOG_TAG,e.getMessage(),e);
e.printStackTrace();
return null;
@Override
protected void onPostExecute(String[] result)
if(result != null)
mForecastAdapter.clear();
for(String DayForecastStr : result)
mForecastAdapter.add(DayForecastStr);
这是日志猫
致命异常：AsyncTask #1 进程：app.com.example.administrator.sunshineapp，PID：19227 java.lang.RuntimeException：执行时发生错误 做背景（） 在 android.os.AsyncTask$3.done(AsyncTask.java:300) 在 java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355) 在 java.util.concurrent.FutureTask.setException(FutureTask.java:222) 在 java.util.concurrent.FutureTask.run(FutureTask.java:242) 在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 在 java.lang.Thread.run(Thread.java:818) 引起：java.lang.NullPointerException：尝试调用虚拟 方法'java.lang.String android.content.Context.getPackageName()' on 空对象引用 在 android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:374) 在 android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:369) 在 app.com.example.administrator.sunshineapp.MainActivityFragment$FetchWeatherTask.formatHighLows(MainActivityFragment.java:90) 在 app.com.example.administrator.sunshineapp.MainActivityFragment$FetchWeatherTask.getWeatherDataFromJson(MainActivityFragment.java:184) 在 app.com.example.administrator.sunshineapp.MainActivityFragment$FetchWeatherTask.doInBackground(MainActivityFragment.java:300) 在 app.com.example.administrator.sunshineapp.MainActivityFragment$FetchWeatherTask.doInBackground(MainActivityFragment.java:74) 在 android.os.AsyncTask$2.call(AsyncTask.java:288) 在 java.util.concurrent.FutureTask.run(FutureTask.java:237) 在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 在 java.lang.Thread.run(Thread.java:818)
这是主要的活动代码：
package app.com.example.administrator.sunshineapp;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.common.api.GoogleApiClient;
public class MainActivity extends AppCompatActivity
public Activity mActivity;
/**
* ATTENTION: This was auto-generated to implement the App Indexing API.
* See https://g.co/AppIndexing/AndroidStudio for more information.
*/
private GoogleApiClient client;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
toolbar.setLogo(R.mipmap.sun);
;
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
@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_refresh)
updateWeather();
return true;
if (id == R.id.action_settings)
startActivity(new Intent(this,SettingsActivity.class));
return true;
return super.onOptionsItemSelected(item);
private void updateWeather ()
MainActivityFragment x = new MainActivityFragment();
MainActivityFragment.FetchWeatherTask WeatherTask = x.new FetchWeatherTask();
SharedPreferences prefs = android.preference.PreferenceManager.getDefaultSharedPreferences(this);
String location = prefs.getString(getString(R.string.pref_location_key),getString(R.string.pref_location_default));
WeatherTask.execute(location);
@Override
public void onStart()
super.onStart();
updateWeather();
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client.connect();
Action viewAction = Action.newAction(Action.TYPE_VIEW, // TODO: choose an action type.
"Main Page", // TODO: Define a title for the content shown.
// TODO: If you have web page content that matches this app activity's content,
// make sure this auto-generated web page URL is correct.
// Otherwise, set the URL to null.
Uri.parse("http://host/path"),
// TODO: Make sure this auto-generated app URL is correct.
Uri.parse("android-app://app.com.example.administrator.sunshineapp/http/host/path"));
AppIndex.AppIndexApi.start(client, viewAction);
@Override
public void onStop()
super.onStop();
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
Action viewAction = Action.newAction(Action.TYPE_VIEW, // TODO: choose an action type.
"Main Page", // TODO: Define a title for the content shown.
// TODO: If you have web page content that matches this app activity's content,
// make sure this auto-generated web page URL is correct.
// Otherwise, set the URL to null.
Uri.parse("http://host/path"),
// TODO: Make sure this auto-generated app URL is correct.
Uri.parse("android-app://app.com.example.administrator.sunshineapp/http/host/path"));
AppIndex.AppIndexApi.end(client, viewAction);
client.disconnect();
【问题讨论】：
什么时候调用formatHighLows？您可能在 Activity 完全初始化之前调用了该函数。 我试图在 OnPreExecute 方法中初始化 sharedPreference 但没有用.....这个方法也在 doInBackground 中被调用 您的异步任务类与活动类不同，对吧？它不是一个片段类，所以你为什么要通过 getActivity() ？您是否尝试单独获取上下文对象？ AsyncTask 是 MainFragmentActivity 的子类......问题是我不明白如何将上下文传递给这个 AsyncTask 在哪里调用 FetchWeatherTask()？我在您发布的代码中没有看到这一点。 【参考方案1】：使用 ActivityName.this 代替 mContext
SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(ActivityName.this)
而不是
SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(mContext)
【讨论】：
不可用！ 什么不可用使用 getDefaultSharedPreferences(MainActivity.this)【参考方案2】：创建一个构造函数并通过该构造函数传递上下文。
【讨论】：
是的，我做到了，但问题仍然存在 只需检查 getApplicationContext() 选项是否可用并尝试一下 SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(mContext); SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(mContext.getApplicationContext()); 试过每个人......似乎没有任何改变......可能是什么问题？！ .......以上是关于AsyncTask 中的 getDefaultSharedPreferences(getActivity())的主要内容，如果未能解决你的问题，请参考以下文章
匿名 AsyncTask 中的构造函数，例如“new AsyncTask<Exercise,Void,Void>()”？
AsyncTask 中的httpClient 需要wakeLock 吗？
无法覆盖 AsyncTask 类中的 onPostExecute() 方法或使其触发