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Trying to call virtual method on null object reference for SharedPreferences in ActionbarActivity Fragment

My application needs to access the shared preference file in the background. Ever since I started using v21 active library support to store my fragment, my application power is shutting down. This command closes whenever the snippet is disconnected from the screen, but the async task is still running and trying to access this sharedpreferences file. Why is this silent about this error and how to fix it?

Here's the stack trace:

12-22 23:49:49.469: E/AndroidRuntime(23016): FATAL EXCEPTION: AsyncTask #4
12-22 23:49:49.469: E/AndroidRuntime(23016): Process: com.bernard.beaconportal.activities, PID: 23016
12-22 23:49:49.469: E/AndroidRuntime(23016): java.lang.RuntimeException: An error occured while executing doInBackground()
12-22 23:49:49.469: E/AndroidRuntime(23016):    at android.os.AsyncTask$3.done(AsyncTask.java:300)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at java.util.concurrent.FutureTask.run(FutureTask.java:242)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at java.lang.Thread.run(Thread.java:818)
12-22 23:49:49.469: E/AndroidRuntime(23016): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.SharedPreferences android.support.v4.app.FragmentActivity.getSharedPreferences(java.lang.String, int)' on a null object reference
12-22 23:49:49.469: E/AndroidRuntime(23016):    at com.bernard.beaconportal.activities.Due_Tommorow_Fragment$Update.doInBackground(Due_Tommorow_Fragment.java:815)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at com.bernard.beaconportal.activities.Due_Tommorow_Fragment$Update.doInBackground(Due_Tommorow_Fragment.java:1)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at android.os.AsyncTask$2.call(AsyncTask.java:288)
12-22 23:49:49.469: E/AndroidRuntime(23016):    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
12-22 23:49:49.469: E/AndroidRuntime(23016):    ... 4 more

Here's the specified line of code where the error occurs:

    SharedPreferences userName = getActivity().getSharedPreferences(
            "Login_Info", Context.MODE_PRIVATE);

Here's an asynchronous task that gets an error:

public class Update extends AsyncTask<String, Void, Void> {

        private final HttpClient Client = new DefaultHttpClient();

        @Override
        protected Void doInBackground(String... urls) {
            SharedPreferences bDay = getActivity().getSharedPreferences(
                    "Login_Info", Context.MODE_PRIVATE);

            String day1 = Integer.toString(bDay.getInt("Day", 0));

            String year1 = Integer.toString(bDay.getInt("Year", 0));

            String month1 = Integer.toString(1 + bDay.getInt("Month", 0));

            SharedPreferences userName = getActivity().getSharedPreferences(
                    "Login_Info", Context.MODE_PRIVATE);

            String day = day1.replaceFirst("^0+(?!$)", "");

            String month = month1.replaceFirst("^0+(?!$)", "");

            String year = year1.replaceFirst("^0+(?!$)", "");

            String birthday = month + "/" + day + "/" + year;

            System.out.println("Birthday = " + birthday);

            String user = userName.getString("username", "");

            // String user = (username).split("@")[0];

            System.out.println("Username = " + user);

            try {

                // HttpClient httpClient = new DefaultHttpClient();
                HttpContext localContext = new BasicHttpContext();
                // HttpGet httpGet = new HttpGet(
                // "http://www.beaconschool.org/~markovic/lincoln.php");

                HttpClient httpclient = new DefaultHttpClient();
                HttpPost httppost = new HttpPost(
                        "http://www.beaconschool.org/~markovic/lincoln.php");

                try {
                    // Add your data
                    List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(
                            2);
                    nameValuePairs
                            .add(new BasicNameValuePair("username", user));
                    nameValuePairs.add(new BasicNameValuePair("birthday",
                            birthday));
                    httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

                    // Execute HTTP Post Request
                    response = httpclient.execute(httppost);

                    Log.d("Http Response:", response.toString());

                } catch (ClientProtocolException e) {
                    // TODO Auto-generated catch block
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                }

                try {
                    Log.d("receiver", "animation stopped and downloaded file");

                    String homework = new Scanner(response.getEntity()
                            .getContent(), "UTF-8").useDelimiter("\\A").next();

                    // String homework =
                    // Html.fromHtml(duetommorow_html).toString();

                    SharedPreferences.Editor localEditor = getActivity()
                            .getSharedPreferences("homework",
                                    Context.MODE_PRIVATE).edit();

                    SimpleDateFormat dateFormat = new SimpleDateFormat(
                            "MM/dd hh:mm a");
                    Calendar cal = Calendar.getInstance();
                    String downloaded = dateFormat.format(cal.getTime());

                    localEditor.putString("homework_content", homework);

                    localEditor.putString("download_date", downloaded);

                    localEditor.apply();

                    localEditor.putString("homework_content", homework);

                    localEditor.apply();

                    Log.d("receiver", "information given to shared preferences");

                    due_tommorow_list.clear();

                    parse_due_tommorow_string();

                    parse_due_tommorow_content();

                } catch (IllegalStateException e) {

                    e.printStackTrace();
                } catch (IOException e) {

                    e.printStackTrace();
                } catch (NullPointerException e) {

                    due_tommorow_list.clear();

                    parse_due_tommorow_string();

                    parse_due_tommorow_content();

                    SharedPreferences.Editor localEditor = getActivity()
                            .getSharedPreferences("homework",
                                    Context.MODE_PRIVATE).edit();

                    localEditor.putString("download_error", "yes");

                    localEditor.apply();

                    e.printStackTrace();
                }

                catch (NoSuchElementException e) {

                    due_tommorow_list.clear();

                    parse_due_tommorow_string();

                    parse_due_tommorow_content();

                    SharedPreferences.Editor localEditor = getActivity()
                            .getSharedPreferences("homework",
                                    Context.MODE_PRIVATE).edit();

                    localEditor.putString("download_error", "yes");

                    localEditor.apply();

                    e.printStackTrace();
                }

                catch (RuntimeException e) {

                    due_tommorow_list.clear();

                    parse_due_tommorow_string();

                    parse_due_tommorow_content();

                    SharedPreferences.Editor localEditor = getActivity()
                            .getSharedPreferences("homework",
                                    Context.MODE_PRIVATE).edit();

                    localEditor.putString("download_error", "yes");

                    localEditor.apply();

                    e.printStackTrace();
                }

            } finally {

            }
            return null;

        }

        @Override
        protected void onPostExecute(Void result) {

            swipeLayout.setRefreshing(false);

            Log.d("sender", "Broadcasting message");

            Intent intent = new Intent("up_navigation");

            intent.putExtra("message", "This is my message!");
            LocalBroadcastManager.getInstance(getActivity()).sendBroadcast(
                    intent);

            Toast.makeText(getActivity(), "Refresh Finished", 4000).show();

            SharedPreferences download_error = getActivity()
                    .getSharedPreferences("homework", Context.MODE_PRIVATE);

            String error = download_error.getString("download_error", "no");

            String download_date = "Download error, refreshed homework using homework downloaded at "
                    + download_error.getString("download_date", "");

            if (error.equals("yes")) {

                SharedPreferences.Editor localEditor = getActivity()
                        .getSharedPreferences("homework", Context.MODE_PRIVATE)
                        .edit();

                Toast.makeText(getActivity(), download_date, Toast.LENGTH_LONG)
                        .show();

                localEditor.putString("download_error", "no");

                localEditor.commit();

            }

            adapter.notifyDataSetChanged();

            swipeLayout.setRefreshing(false);

        }

    }
+3


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3 answers


You are doing something time-consuming in AsyncTask

, when the part getActivity()

is being executed, the action was destroyed. Thus, the link getActivity()

returns null, which is quite correct.

What you have to do is in Thread

or AsyncTask

, you should always check if it is getActivity()

null, in the case Activity

that your put Fragment

it was destroyed.



I don't think @ I'm_With_Stupid's answer is a good mark because it's bad to keep the link Activity

in yours Fragment

and the snippet has already done that for you.

+10


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One way to get rid of this is to keep the activity reference when calling onAttach and use the activity reference wherever needed, like

@Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        mActivity = activity;
    }

Now at the top of your activity put:



private Activity mActivity;

And for every SharedPreference that gives you a problem, replace "getActivity ()" with "mActivity"

+5


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maybe you need a Context in your code, for example:

 public String getBulbsUrl(Context mcontext) {
    SharedPreferences preferences = mContext.getSharedPreferences("Bublurl",0);
    String url = preferences.getString("url","http://");
    return url;
}
+1


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