Adapter.notifyDataSetChanged（）在onCreate（）中不起作用

Question

I am trying to parse JSON using Volley.

I am using a vector to store parsed data and calling adapter.notifyDataSetChanged() inside onCreate() after filling vector. But no changes are there.

If I am calling adapter.notifyDataSetChanged() inside try-catch block of getData() then it is working fine. Why?

public class MainActivity extends AppCompatActivity{

    Vector<Data> ve;
    private  Adapter adapter;
    RecyclerView recyclerView;
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        recyclerView=(RecyclerView)findViewById(R.id.main_recycler_view);
        ve=new Vector<Data>();
        adapter=new Adapter(ve);
        RecyclerView.LayoutManager lm=new LinearLayoutManager(getApplicationContext());
        recyclerView.setLayoutManager(lm);
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setAdapter(adapter);

        getData(ve);
        adapter.notifyDataSetChanged();  //not working
    }
    public void getData(final Vector<Data> ve)
    {
        String url = "https://api.androidhive.info/contacts/";
        StringRequest request = new StringRequest(url, new Response.Listener<String>() {
            @Override
            public void onResponse(String jsonString) {
                try
                {
                    JSONObject object = new JSONObject(jsonString);
                    JSONArray arr = object.getJSONArray("contacts");
                    int len=arr.length();
                    JSONObject obj;
                    for (int i = 0; i < len; i++)
                    {
                        obj = arr.getJSONObject(i);
                        ve.add(new Data(obj.getString("name"), obj.getString("email"));

                    }
                   //adapter.notifyDataSetChanged();working
                }
                catch (JSONException e)
                {
                    Toast.makeText(getApplicationContext(),"JSON Parsing Exception",Toast.LENGTH_LONG);
                    e.printStackTrace();
                }

            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError volleyError) {
                Toast.makeText(getApplicationContext(), "Some error occurred!!", Toast.LENGTH_SHORT).show();

            }
        });
        RequestQueue rQueue = Volley.newRequestQueue(this);
        rQueue.add(request);

    }

}

Answer 1

you cannot do that reason nothing volley used network requests which are designed to be asynchronous in nature , so the network request is put in queue and code continues to execute the notifyadapter changed method . The response to the network call occurs afterwards and add data, you should call that method after data is received by calling it inside volley on response method