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
notifyDataSetChanged();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:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.all_candidatos);
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
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(Monitorizacion.this);
pDialog.setMessage("Loading ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* 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
candidatosList.add(map);
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
pDialog.dismiss();
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,
TAG_DNI, TAG_NOMBRE, TAG_TEST, TAG_PREGUNTA, TAG_BATERIA},
new int[] { R.id.id, R.id.dni, R.id.nombre, R.id.test, R.id.pregunta, R.id.bateria});
setListAdapter(adapter);
adapter.notifyDataSetChanged();
// timer();
}
});
}
}
}
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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:
- Initialise the
arrayListwhile declaring it globally. - 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
arrayListit will take care of it, but never loose the reference. - Always modify the data in the arrayList itself (if your data is completely new
than you can call
adapter.clear()andarrayList.clear()before actually adding data to the list) but don't set the adapter i.e If the new data is populated in thearrayListthan justadapter.notifyDataSetChanged()
Stay true to the Documentation.
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