Commit Fragment onPostexec

Issue

I am new to Android development and have a problem with commit my Fragment. When the Async Task is finished I try to commit the Fragment from the OnPost Method, but The App destroys. If I commit the Fragment normally from the MapsActivity.class everything works fine.

 @Override
    protected void onPostExecute(String s) {


        try {
            JSONObject jsonObject = new JSONObject(s);
            JSONArray jsonArray = jsonObject.getJSONArray("routes").getJSONObject(0).getJSONArray("legs").getJSONObject(0).getJSONArray("steps");
            int count = jsonArray.length();


            Log.i("Distance", jsonArray.toString());




            String[] polyline_array = new String[count];
            JSONObject jsonObject2;
            JSONObject jsonObject3;
            for (int i =0;i<count;i++){

                jsonObject2 = jsonArray.getJSONObject(i);

                String polygone = jsonObject2.getJSONObject("polyline").getString("points");


                polyline_array[i] = polygone;

            }

            distancetotal = 0;

            for (int i =0;i<count;i++){
                jsonObject3 = jsonArray.getJSONObject(i);
                String distance = jsonObject3.getJSONObject("distance").getString("value");






                    this.distancetotal += Double.valueOf(distance);




            }





            float umweg =  ((totaldistance/distancetotal)-1)*100;
             umwegint = (int) umweg;




            MapsActivity mapsActivity = new MapsActivity();
            mapsActivity.a = String.valueOf(distancetotal);
            mapsActivity.c = String.valueOf(umwegint);
            mapsActivity.updateUi();

            int count2 = polyline_array.length;
            for (int i = 0; i< count2;i++){

                PolylineOptions options2 = new PolylineOptions();
                options2.color(Color.GREEN);
                options2.width(10);
                options2.addAll(PolyUtil.decode(polyline_array[i])).geodesic(true);



                mMap.addPolyline(options2);






            }





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


    }

MapsActivity.class

 public class MapsActivity extends FragmentActivity implements  OnMapReadyCallback, View.OnClickListener, RoutingListener{

    public void updateUi(){


            Fragment newfragment = new ResultFragment();
            fragmentTransaction = getSupportFragmentManager().beginTransaction();
            fragmentTransaction.replace(R.id.fragment4, newfragment);
            fragmentTransaction.commit();

        }

}

java.lang.IllegalStateException: Activity has been destroyed
                  at 

android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:2087)
                      at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:678)
                      at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:632)
                      at taxiapp.com.taxitracker.MapsActivity.updateUi(MapsActivity.java:607)
                      at taxiapp.com.taxitracker.GetDirectionsData.onPostExecute(GetDirectionsData

Solution

I guess in MapsActivity you start an async task by calling GetDirectionsData (that extends from AsyncTask), when the task completed, you return result toMapsActivity` to update UI.

Root cause: These lines of code make your app crash

MapsActivity mapsActivity = new MapsActivity();
mapsActivity.a = String.valueOf(distancetotal);
mapsActivity.c = String.valueOf(umwegint);
mapsActivity.updateUi();

Why: In Android you do not allowed to create an activity instance, the system will create for you and call onCreate method to notify you the activity has been created. When you create a new instance of MapsActivity and call updateUi method, the system cannot find the activity (because the activity created by you not the system) anywhere and they think the activity might be destroy.

Solution: Add these lines of code in GetDirectionsData class

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

    // Add this line
    private WeakReference<MapsActivity> mapsActivityWeakReference;

    // Add this constructor
    public GetDirectionsData(MapsActivity mapsActivity) {
        mapsActivityWeakReference = new WeakReference<>(mapsActivity);
    }

    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);

        // Your code
        float umweg =  ((totaldistance/distancetotal)-1)*100;
        umwegint = (int) umweg;

        // Remove these lines of code
        /*MapsActivity mapsActivity = new MapsActivity();
        mapsActivity.a = String.valueOf(distancetotal);
        mapsActivity.c = String.valueOf(umwegint);
        mapsActivity.updateUi();*/

        // Add these lines of code instead
        MapsActivity mapsActivity = mapsActivityWeakReference.get();
        if (mapsActivity != null) {
            mapsActivity.a = String.valueOf(distancetotal);
            mapsActivity.c = String.valueOf(umwegint);
            mapsActivity.updateUi();
        }

        int count2 = polyline_array.length;
        // Your code
    }
}

In MapsActivity class

DirectionsData directionsData = new GetDirectionsData(this);
directionsData.execute();

Answered By - Son Truong