Katherine99 Katherine99 - 4 years ago 142
Android Question

Android: notifyDataSetChanged(); not working

I have a database in a server and from a Tablet I take some values from one table in the database. I load this information correctly into a list but I would like to know why when there is a change, nothing happens even if I use

. I must say that for loading the loading data y use the AsyncTaskClass
So, my problem is that I don't know if use the notifyDataSetChanged(); method correctly ,because if there's is a change I would like to refresh the image. Here is some part of the code of the class:

public void onCreate(Bundle savedInstanceState) {

candidatosList = new ArrayList<HashMap<String, String>>();

new CargarCandidatos().execute();

// public void timer(){
// new CountDownTimer(tiempo, 100) {
// public void onTick(long millisUntilFinished) {
// }
// public void onFinish() {
// // new CargarCandidatos().execute();
// }
// }.start();}

* Background Async Task to Load all product by making HTTP Request
* */
class CargarCandidatos extends AsyncTask<String, String, String> {

* Before starting background thread Show Progress Dialog
* */
protected void onPreExecute() {
pDialog = new ProgressDialog(Monitorizacion.this);
pDialog.setMessage("Loading ...");

* getting All products from url
* */
protected String doInBackground(String... args) {
List<NameValuePair> params = new ArrayList<NameValuePair>();
JSONObject json = jParser.makeHttpRequest(url_candidatos, "GET", params);

Log.d("Candidatos: ", json.toString());

try {
int success = json.getInt(TAG_SUCCESS);

if (success == 1) {

candidatos = json.getJSONArray(TAG_CANDIDATOS);

for (int i = 0; i < candidatos.length(); i++) {
JSONObject c = candidatos.getJSONObject(i);

// Storing each json item in variable
String nserie = c.getString(TAG_NSERIE);
String dni = c.getString(TAG_DNI);
String nombre = c.getString(TAG_NOMBRE);
String test = c.getString(TAG_TEST);
String pregunta = c.getString(TAG_PREGUNTA);
String bateria = c.getString(TAG_BATERIA);

// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();

// adding each child node to HashMap key => value
map.put(TAG_NSERIE, nserie);
map.put(TAG_DNI, dni);
map.put(TAG_NOMBRE, nombre);
map.put(TAG_TEST, test);
map.put(TAG_PREGUNTA, pregunta);
map.put(TAG_BATERIA, bateria);

// adding HashList to ArrayList
} catch (JSONException e) {

return null;

* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
runOnUiThread(new Runnable() {
public void run() {
* Updating parsed JSON data into ListView
* */
adapter = new SimpleAdapter(
Monitorizacion.this, candidatosList,
R.layout.list_item, new String[] { TAG_NSERIE,
new int[] { R.id.id, R.id.dni, R.id.nombre, R.id.test, R.id.pregunta, R.id.bateria});
// timer();



Answer Source

One of the main reasons notifyDataSetChanged() won't work for you - is,

Your adapter loses reference to your list.

When you first initialise the Adapter it takes a reference of your arrayList and passes it to its superclass. But if you reinitialise your existing arrayList it losses the reference, and hence, the communication channel with Adapter.

When creating and adding a new list to the Adapter. Always follow these guidelines:

  1. Initialise the arrayList while declaring it globally.
  2. Add the List to the adapter directly with out checking for null and empty values . Set the adapter to the list directly (don't check for any condition). Adapter guarantees you that wherever you make changes to the data of the arrayList it will take care of it, but never loose the reference.
  3. Always modify the data in the arrayList itself (if your data is completely new than you can call adapter.clear() and arrayList.clear() before actually adding data to the list) but don't set the adapter i.e If the new data is populated in the arrayList than just adapter.notifyDataSetChanged()

Stay true to the Documentation.

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