Custom Listview Won't Display with Volley Request

Question

I have created a Custom Listview that will display area list from my database but sometimes the data won't display. After staying in the activity for a couple of seconds and restarting the activity again it will display the list. Here is my code can you check this out ? If see what's the problem. Thanks!

AreaListActivity.java

private ListAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    setupActionBar();

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    getSupportActionBar().setDisplayShowHomeEnabled(true);

}

@Override
protected void onResume() {
    super.onResume();
    setupList();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    // handle arrow click here
    if (item.getItemId() == android.R.id.home) {
        finish(); // close this activity and return to preview activity (if there is any)
    }
    return super.onOptionsItemSelected(item);
}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    // Only if you need to restore open/close state when
    // the orientation is changed
    if (adapter != null) {
        adapter.saveStates(outState);
    }
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);

    // Only if you need to restore open/close state when
    // the orientation is changed
    if (adapter != null) {
        adapter.restoreStates(savedInstanceState);
    }
}

private void setupList() {

    ListView listView = (ListView) findViewById(R.id.list_view);
    adapter = new ListAdapter(this, createList());
    listView.setAdapter(adapter);
}

private List<String> createList() {
    final List<String> list = new ArrayList<>();

    Response.Listener<String> responseListener = new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            try {
                JSONArray jsonArray = new JSONArray(response);
                for (int i = 0; i < jsonArray.length(); i++) {

                    JSONObject obj = jsonArray.getJSONObject(i);
                    String areaName = obj.getString("area_name");
                    list.add(areaName);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    };

    GetAreaListRequest registerRequest = new GetAreaListRequest("True", responseListener);
    RequestQueue queue = Volley.newRequestQueue(AreaListActivity.this);
    queue.add(registerRequest);

    return list;
}

private void setupActionBar() {
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    if (getSupportActionBar() != null) {
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setDisplayShowHomeEnabled(true);

        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });
    }
}

GetAreaListRequest.java

public class GetAreaListRequest extends StringRequest {

private static final String GET_AREA_LIST_URL = "http://192.168.1.7:8080/smsams/get_area_list.php";
private Map<String, String> params;

public GetAreaListRequest(String get_area_status, Response.Listener<String> listener) {
    super(Method.POST, GET_AREA_LIST_URL, listener, null);

    params = new HashMap<>();
    params.put("get_area_status", get_area_status);

}

@Override
public Map<String, String> getParams() {
    return params;
}

ListAdapter.java

class ListAdapter extends ArrayAdapter<String> {
private final LayoutInflater mInflater;
private final ViewBinderHelper binderHelper;
private Context context;

ListAdapter(Context context, List<String> objects) {
    super(context, R.layout.row_list, objects);
    mInflater = LayoutInflater.from(context);
    binderHelper = new ViewBinderHelper();
    this.context = context;
    // uncomment if you want to open only one row at a time
    // binderHelper.setOpenOnlyOne(true);
}

@NonNull
@Override
public View getView(int position, View convertView, @NonNull ViewGroup parent) {
    final ViewHolder holder;

    if (convertView == null) {
        convertView = mInflater.inflate(R.layout.row_list, parent, false);

        holder = new ViewHolder();
        holder.textView = (TextView) convertView.findViewById(R.id.text);
        holder.statView = convertView.findViewById(R.id.statistic_layout);
        holder.mapView = convertView.findViewById(R.id.map_layout);
        holder.infoView = convertView.findViewById(R.id.info_layout);
        holder.swipeLayout = (SwipeRevealLayout) convertView.findViewById(R.id.swipe_layout);

        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }

    final String item = getItem(position);
    if (item != null) {
        binderHelper.bind(holder.swipeLayout, item);

        holder.textView.setText(item);
        holder.statView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent i = new Intent(context, StatisticActivity.class);
                context.startActivity(i);
            }
        });
        holder.mapView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent i = new Intent(context, MapsActivity.class);
                i.putExtra("soilArea", holder.mapView.toString());
                context.startActivity(i);
            }
        });
        holder.infoView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent i = new Intent(context, InfoViewActivity.class);
                context.startActivity(i);
            }
        });
    }

    return convertView;
}

/**
 * Only if you need to restore open/close state when the orientation is changed.
 * Call this method in {@link android.app.Activity#onSaveInstanceState(Bundle)}
 */
void saveStates(Bundle outState) {
    binderHelper.saveStates(outState);
}

/**
 * Only if you need to restore open/close state when the orientation is changed.
 * Call this method in {@link android.app.Activity#onRestoreInstanceState(Bundle)}
 */
void restoreStates(Bundle inState) {
    binderHelper.restoreStates(inState);
}

private class ViewHolder {
    TextView textView;
    View statView;
    View mapView;
    View infoView;
    SwipeRevealLayout swipeLayout;
}

Answer 1

The network requests usually happens in an asynchronous way. So there is no specific time that the onResponse() gets called. So in your createList() method you initialised an empty arraylist and before the request produces the response(asynchronously calls onResponse) the list which contains no value is returned.

You can change your code something like this:

In createList():

Response.Listener<String> responseListener = new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
        try {
            JSONArray jsonArray = new JSONArray(response);
            for (int i = 0; i < jsonArray.length(); i++) {

                JSONObject obj = jsonArray.getJSONObject(i);
                String areaName = obj.getString("area_name");
                list.add(areaName);
                adapter = new ListAdapter(this, list);
                listView.setAdapter(adapter);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
};

So here the adapter is set only after the data is pulled from the network.

Answer 2

Try this:

 private  List<String> list = new ArrayList<>(); 
    private void setupList() {

        ListView listView = (ListView) findViewById(R.id.list_view);
        adapter = new ListAdapter(this, list);
        listView.setAdapter(adapter);
    }

    private void createList() {


        Response.Listener<String> responseListener = new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                try {
                    JSONArray jsonArray = new JSONArray(response);
                    for (int i = 0; i < jsonArray.length(); i++) {

                        JSONObject obj = jsonArray.getJSONObject(i);
                        String areaName = obj.getString("area_name");
                        list.add(areaName);
                    }
                    adapter.notifyDataSetChanged();
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            }
        };

        GetAreaListRequest registerRequest = new GetAreaListRequest("True", responseListener);
        RequestQueue queue = Volley.newRequestQueue(AreaListActivity.this);
        queue.add(registerRequest);


    }