Android ViewPager Frame Listview Crash

Question

I am trying to make a TabLayout (ViewPager) App with Three Fragments. In one of those tabs, I want display a json parsed custom list view. The Custom list view and Tab Layout works fine individually (codes from tutorial). When I combine these two, App crashes immediately, I couldn't figure out what is going wrong. Hope you guys can help

Thank you Sam_0829....you saved me

The Problems were 1. Instead of MainActivity, Getmessages must be in Fragment

2. View Was empty while calling onViewCreated, So i declared a private view variable

   private View v;

   //then onCreate

   View v = inflater.inflate(R.layout.message_tab, container, false);

   and passed it into

onViewCreated public void onViewCreated(View v, @Nullable Bundle savedInstanceState) { super.onViewCreated(v, savedInstanceState); contactList = new ArrayList<>();

    lv = (ListView) v.findViewById(R.id.list);

    new Getmessages().execute();
}

and life became awesome

Thank yo sam you taught me to trouble shoot via logs...something i never trusted before

Message Fragment (Solved Code) ->

    package com.example.user.newton;

 public class MessageTab extends Fragment {
    private String TAG = MainActivity.class.getSimpleName();

    private ProgressDialog pDialog;
    private ListView lv;
    private View v;
    // URL to get messages JSON

    private static String url = "http://myjson.com/17oyz5";

    ArrayList<HashMap<String, String>> contactList;
    private MainActivity.SectionsPagerAdapter mSectionsPagerAdapter;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment

       View v =  inflater.inflate(R.layout.message_tab, container, false);
        return v;
    }
    private class Getmessages extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Showing progress dialog
            pDialog = new ProgressDialog(getActivity());
            pDialog.setMessage("Please wait...");
            pDialog.setCancelable(false);
            pDialog.show();

        }

        @Override
        protected Void doInBackground(Void... arg0) {
            HttpHandler sh = new HttpHandler();

            // Making a request to url and getting response
            String jsonStr = sh.makeServiceCall(url);

            Log.e(TAG, "Response from url: " + jsonStr);

            if (jsonStr != null) {
                try {
                    JSONObject jsonObj = new JSONObject(jsonStr);

                    // Getting JSON Array node
                    JSONArray messages = jsonObj.getJSONArray("messages");

                    // looping through All messages
                    for (int i = 0; i < messages.length(); i++) {
                        JSONObject c = messages.getJSONObject(i);

                        String message= c.getString("message");
                        String sender= c.getString("sender");
                        String mtime= c.getString("time");

                        HashMap<String, String> contact = new HashMap<>();

                        // adding each child node to HashMap key => value
                        contact.put("message", message);
                        contact.put("sender", sender);
                        contact.put("mtime", mtime);

                        contactList.add(contact);
                    }
                } catch (final JSONException e) {
                    Log.e(TAG, "Json parsing error: " + e.getMessage());
                    getActivity().runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Toast.makeText(getActivity(),
                                    "Json parsing error: " + e.getMessage(),
                                    Toast.LENGTH_LONG)
                                    .show();
                        }
                    });

                }
            } else {
                Log.e(TAG, "Couldn't get json from server.");
                getActivity().runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getActivity(),
                                "Couldn't get json from server. Check LogCat for possible errors!",
                                Toast.LENGTH_LONG)
                                .show();
                    }
                });

            }

            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // Dismiss the progress dialog
            if (pDialog.isShowing())
                pDialog.dismiss();
            /**
             * Updating parsed JSON data into ListView
             * */
            ListAdapter adapter = new SimpleAdapter(
                    getActivity(), contactList,
                    R.layout.custom_layout, new String[]{"message", "sender",
                    "mtime"}, new int[]{R.id.name,
                    R.id.email, R.id.mobile});

            lv.setAdapter(adapter);
        }

    }

    @Override
    public void onViewCreated(View v, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(v, savedInstanceState);
        contactList = new ArrayList<>();

        lv = (ListView) v.findViewById(R.id.list);

        new Getmessages().execute();
    }
}

MessageFragment Layout

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

Answer 1

if (lv!= null) {

lv.setAdapter(adapter)

}

Answer 2

Please change

pDialog = new ProgressDialog(getApplicationContext());

to

pDialog = new ProgressDialog(MainActivity.this);

& try.

Answer 3

It looks like you are trying to update the ListView contents in the wrong place : you're referencing the ListView as lv in your MainActivity, but it needs to be updated in your MessageFragment. You should move your Getmessages to (for example) onCreateView of your MessageFragment instead.