Asynctask result shows after recreating fragment

Issue

In my app I get data from the user in a fragment and use the entered data to get result by JSON using AsyncTask then save it to database then display it in another fragment.

The problem is when I execute the asyncTask and open the fragment the data doesn't show unless I rotate the device (force fragment recreation).

My first fragment code:

...
SecondFragment secondFragment = new SecondFragment();
new SecondFragment.GetTask("s").execute(URL);
FragmentTransaction ft =getActivity().getSupportFragmentManager().beginTransaction();
ft.setCustomAnimations(R.anim.slide_in_up, R.anim.slide_in_up);
ft.add(R.id.s_con, secondFragment).addToBackStack("back").commit();
...

Second Fragment code:

...
recyclerView.setAdapter(new SAdapter(getContext(),R.layout.group_header));
...

public static class GetTask extends AsyncTask<String, String, Void> {

    String arrayname;


    GetTask(String arrayname) {
        this.arrayname = arrayname;
    }


    }

    @Override
    protected Void doInBackground(String... params) {
        HttpURLConnection connection = null;
        BufferedReader reader = null;

        try {
            URL url = new URL(params[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();

            InputStream stream = connection.getInputStream();

            reader = new BufferedReader(new InputStreamReader(stream));
            StringBuffer buffer = new StringBuffer();

            String line = "";
            while ((line = reader.readLine()) != null) {
                buffer.append(line);
            }

            String finalJson = buffer.toString();

            JSONObject parentObject = new JSONObject(finalJson);
            JSONObject secondParentObject = parentObject.getJSONObject("data");


            //json getter and adder to database
            JSONArray Array = secondParentObject.getJSONArray(arrayname);
            for (int i = 0; i < Array.length(); i++) {
                JSONObject finalObject = Array.getJSONObject(i);
                switch (arrayname) {
                    case "s":
                        db.SAddJson(finalObject);
                        break;
                }
            }


        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        } finally {
            if (connection != null) {
                connection.disconnect();
            }
            try {
                if (reader != null) {
                    reader.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
    }
}

Solution

AsyncTask executes in another thread. Second fragment is not updated because the asynctask was still executing when you loaded it. When you changed orientation it simple recreated second fragment by then Asynctask finished its task that's why it got updated. Move AsyncTask to first fragment and load the 2nd fragment in the Async task's onPostExecute(). onPostExecuted() runs in the UI thread.

When using AsyncTask inside a fragment, there might be scenarios like orientation change where the activity will get recreated and this can cause your fragment to be recreated as well and the AsyncTask will be called again. This can also cause memory leak. To avoid this call the method inside your onCreate() of first Fragment;

setRetainInstance(true);

This will not kill the fragment on orientation change and it will be safer. To know more about handling orientation change check out this link:

https://developer.android.com/guide/topics/resources/runtime-changes.html

Answered By - Harikumar Alangode