Async Task gets Crashed when app is in background

Question

I am Calling Asynctask to get response from the Json Service and setting the list in the post execute. Its working fine but when I open any other applications and then again open my app. I am getting NPE in the post execute. Any idea why its happening. Any Help Would be greatly appreciated.

    public class AsyncTaskParks extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        utility.showProgress(getActivity(), "Please Wait", "Loading..");
    }

    @Override
    protected String doInBackground(String... params) {
        // TODO Auto-generated method stub
        String response = mServiceHandler
                .getSoapResponseByMethod("GetSiteList");
        Log.d("Response: ", "> " + response);

        if (response != null) {

            try {

                JSONObject jsonObject = new JSONObject(response);
                JSONArray rows = jsonObject.getJSONArray("Rows");
                for (int i = 0; i < rows.length(); i++) {
                    JSONObject c = rows.getJSONObject(i);

                    infoParks = new InfobeanParks();

                    String siteId = c.getString("SiteID");
                    infoParks.setSiteId(siteId);

                    String siteType = c.getString("SiteType");
                    infoParks.setSiteType(siteType);

                    String siteName = c.getString("SiteName");
                    infoParks.setSiteName(siteName);

                    String siteShortName = c.getString("SiteShortName");
                    infoParks.setSiteShortName(siteShortName);

                    String siteImage = c.getString("SiteImage");
                    infoParks.setSiteImage(siteImage);
                    if (siteType.equalsIgnoreCase("P")) {
                        lstPark.add(infoParks);

                    }

                }

            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return response;
    }

    @Override
    protected void onPostExecute(String result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        utility.dismissProgress();

        gridviewParks.setAdapter(new GridviewParksAdapter(getActivity(),
                lstPark));

    }
}

08-28 00:58:15.911: E/AndroidRuntime(3720): FATAL EXCEPTION: main
08-28 00:58:15.911: E/AndroidRuntime(3720): Process: com.oceancity.ocparks, PID: 3720
08-28 00:58:15.911: E/AndroidRuntime(3720): java.lang.NullPointerException
08-28 00:58:15.911: E/AndroidRuntime(3720):     at      com.ocparks.adapter.GridviewParksAdapter.<init>(GridviewParksAdapter.java:47)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at    com.ocparks.FragmentParks$AsyncTaskParks.onPostExecute(FragmentParks.java:201)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at com.ocparks.FragmentParks$AsyncTaskParks.onPostExecute(FragmentParks.java:1)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at   android.os.AsyncTask.finish(AsyncTask.java:632)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at    android.os.AsyncTask.access$600(AsyncTask.java:177)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at android.os.Handler.dispatchMessage(Handler.java:102)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at android.os.Looper.loop(Looper.java:136)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at android.app.ActivityThread.main(ActivityThread.java:5086)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at java.lang.reflect.Method.invokeNative(Native Method)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at java.lang.reflect.Method.invoke(Method.java:515)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
08-28 00:58:15.911: E/AndroidRuntime(3720):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

You can't change the views of an inactive Activity. You need to check that the Activity is still running in the onPostExecute or better yet, just cancel the ASyncTask completely in the onPause or onStop methods.

public void onPause() {
    super.onPause();

    if (mAsyncTaskParks != null){
        mAsyncTaskParks.cancel();
     }
}

The benefit of this second method is that it will call ASyncTask's onCancelled method which will allow you to cancel the network call, if that's what you want to do.