Develop Reference

Why does ArrayAdapter fail to update listview after activity restart?

I have an activity that in onCreate() does the following:
Creates an empty ArrayList
Creates a new ArrayAdapter associated with the above ArrayList
Sets ListView to use the above ArrayAdapter
Uses Volley to send a GET request to my API to fetch some JSON data to load into the ListView
Once the data is fetched I add it to my ArrayList and the ListView is populated as expected
My problem is that when the activity is restarted (i.e. the screen is rotated via the emulator or the activity is restarted through Android Studio) the ListView no longer populates.
I am not saving any state. I expect the activity to return to its initial default state so I don't think onSaveInstanceState() is the answer.
I've verified that the data is returned successfully from the API and that the adapter's hashcode is the same before and after the volley request and that it equals the ListView's set adapter. I've also verified that onDestroy() and then onCreate() are called when the activity is restarted so I know it is going through a full life cycle.
If I rotate the screen programmatically with setRequestedOrientation() I don't experience this issue. If I add items to my ArrayList outside of the GET request callback, I don't experience this issue.
Here is my activity onCreate()
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
//The data to be displayed
descriptions = new ArrayList<>();
listView = (ListView)this.findViewById(R.id.myListView);
//Link 'descriptions' to the adapter
adapter = new ArrayAdapter<>(this, R.layout.list_json_text_view, descriptions);
listView.setAdapter(adapter);
this.addTextFilter();
this.addListViewClickListener();
//See my ApiGetRequest class below
request = new ApiGetRequest();
request.send(this.getContext(), getDataUrl(), this, "", REQUEST_TYPES.TEXT);
}
And my activity GET request callback
public void onSuccess(DescriptiveJSONArray items, REQUEST_TYPES type) {
descriptions.clear();
try {
for (int i = 0; i < items.length(); ++i) {
JSONObject obj = items.getJSONObject(i);
String desc = obj.optString("name", "") + " " + obj.optString("description", "");
//TODO: Remove debug code
System.out.println("Adding: "+desc);
descriptions.add(desc);
}
}
catch(JSONException e) {
e.printStackTrace();
//getJSONObject failed
}
}
And my ApiGetRequest methods
//My activity implements ApiGetCallback
public void send(Context context, String url, ApiGetCallback callback, String tag, REQUEST_TYPES type) {
StringRequest stringRequest = getStringRequest(url, callback, tag, type);
//Singleton wrapper for RequestQueue
AppRequestQueue queue = AppRequestQueue.getInstance(context);
queue.add(stringRequest);
}
//Inner class inside ApiGetCallback
class SuccessListener implements Response.Listener<String> {
ApiGetCallback callback;
REQUEST_TYPES type;
public SuccessListener(ApiGetCallback callback, REQUEST_TYPES type) {
this.callback = callback;
this.type = type;
}
#Override
public void onResponse(String response) {
try {
DescriptiveJSONArray jsonResp = new DescriptiveJSONArray(response);
callback.onSuccess(jsonResp, type);
}
catch(JSONException e) {
callback.onJsonException(e);
}
}
}
Any ideas what is happening?. I'm testing on Marshmallow and Nougat

You are missing a call to notifyDataSetChanged, after the onSuccess function is done.

you may need to override onStart and do update anything in it

adapter = new ArrayAdapter<>(this, R.layout.list_json_text_view, descriptions);
listView.setAdapter(adapter);
//See my ApiGetRequest class below
request = new ApiGetRequest();
request.send(this.getContext(), getDataUrl(), this, "", REQUEST_TYPES.TEXT);
use this part of code in onResume method.

android how to set notifySetDataChanged() for an ArrayList

I'm trying to refresh a ListView contents when I go back to the activity from another activity. It only refresh contents when I go back further to main app screen and come back.
This is my Activity where I set the ListView and it's adapter:
public static final String ID = "Id";
public static final String iidd = "iidd";
private static final String DESC = "Description";
private AppCompatDelegate delegate;
Cursor c;
ListView listFood;
SimpleAdapter myAdapter;
ArrayList<Map<String, String>> names = new ArrayList<Map<String, String>>();
Integer i_d;
Integer iddd;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activityfood_main);
listFood = (ListView) findViewById(R.id.listViewF);
listFood.setOnItemClickListener(viewFoodListener);
// database read
DatabaseConnectorFood db = new DatabaseConnectorFood(this);
db.open();
c = db.getFoodData();
while(c.moveToNext()) {
Map<String, String> data = new HashMap<String, String>(2);
data.put("Description", c.getString(c.getColumnIndex("Description")));
data.put("Serving_Size", c.getString(c.getColumnIndex("Serving_Size")));
names.add(data);
}
db.close();
myAdapter = new SimpleAdapter(this, names, R.layout.list_food,
new String[] {"Description", "Serving_Size"},
new int[] {R.id.ViewFoodNotesOne, R.id.ViewFoodNotesTwo});
listFood.setAdapter(myAdapter);
}
I tried to add this under onResume() but it doesn't work
#Override
protected void onResume() {
super.onResume();
myAdapter.notifyDataSetChanged();
}
EDIT: i followed the suggestion by answers below doing as follow, but with no results:
#Override
protected void onResume() {
super.onResume();
DatabaseConnectorFood db = new DatabaseConnectorFood(this);
db.open();
c = db.getFoodData();
while(c.moveToNext()) {
Map<String, String> data = new HashMap<String, String>(2);
data.put("Description", c.getString(c.getColumnIndex("Description")));
data.put("Serving_Size", c.getString(c.getColumnIndex("Serving_Size")));
names.add(data);
}
db.close();
myAdapter = new SimpleAdapter(this, names, R.layout.list_food,
new String[] {"Description", "Serving_Size"},
new int[] {R.id.ViewFoodNotesOne, R.id.ViewFoodNotesTwo});
// Set the Adapter into SimpleCursorAdapter
listFood.setAdapter(myAdapter);
myAdapter.notifyDataSetChanged();
}
SOLVED: added names.clear(); to the code over here, above everything, to clear the ListView first as #Rami suggested, and it works! thanks

1) To refresh your list, you need to clear your data (names) then reload it again from the database.
2) onResume() method is frequently called. For better performance, i suggest you to use onActivityResult() instead, while you update your data from the childs activities.
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// refresh your list here.
}
In this case, don't forget to use startActivityForResult() instead of startActivity().

adapter.notifyDataSetChanged() is used to tell the ListView that the items in the dataset have changed.
You need to modify the actualy dataset for it to have any visual effects, since by just invoking the method the same values will be displayed before and after the method was called.
If you want to keep this approach, you would need to query the database again in onResume to reload your data. Then call adapter.notifyDataSetChanged().

onCreate doesn't called when you go back with onBackPressed(); you need to put all logick with setting data to adapter in onResume() method

I suggest using a SimpleCursorAdapter instead of a SimpleAdapter. It will take care of all the details for you when the data changes in your database.

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();. 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:
#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();
}
});
}
}
}

One of the main reasons notifyDataSetChanged() won't work for you - is,
Your adapter loses reference to your list.
When you first initialize the Adapter it takes a reference of your arrayList and passes it to its superclass. But if you reinitialize your existing arrayList it loses 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 arrayList while declaring it globally.
Add the List to the adapter directly without 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
lose the reference.
Always modify the data in the arrayList itself (if your data is completely new then 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.

The thing you need to edit is put your
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();
}
});
into the OnCreate(). and return the list candidatosList from Asynctask. than set timer for updating candidatosList list.

It might be worth checking if you have an empty override for registerDataSetObserver(). Android Studio added one for me without implementing the call to super. Adding it in as follows was enough to get my listView working again:
#Override
public void registerDataSetObserver(DataSetObserver observer) {
super.registerDataSetObserver(observer);
}

An adapter define the comportement of the layout !
-> setListAdapter() : Define the adapter for a ListView/GridView/Gallery...
but you need to specify the data !
I recommend to you, to initialize 'setListAdapter' in the 'onCreate' or in the constructor.
After you set the data into the adapter (exemple : adapter.setItem(yourData))
And NOW ! You should to call notifyDataSetChanged !
Because you have changed the data but the view isn't refresh and notifydatasetchanged() reload the content of the view (ListView/GridView/Gallery...)
For a good practice and understand correctly I recommend to you to use a 'custom adapter' using 'baseAdapter'
Read and do this tutorial (I haver learn with this): http://www.androidhive.info/2012/02/android-custom-listview-with-image-and-text/
Read the documentation : http://developer.android.com/reference/android/widget/BaseAdapter.html

The update function should be called from UI thread.
My answer is actually similar to #user1621629's answer with that difference that I am using rxJava, so here's working code that solve this problem for me:
this.subscriber = myAdapter.getSubscriber(); // keep for unsubscribe in destroy
dataSource.subscribeOn(Schedulers.computation()).observeOn(AndroidSchedulers.mainThread()).subscribe(this.subscriber);
So I set all execution in order to get data for the list to computation thread, but showing result in UI thread.
Here's how I create subscriber for this:
public class MyListAdapter extends RecyclerView.Adapter<LocationListAdapter.ViewHolder> {
private List<ListItem> mDataset = new ArrayList<>();
public Subscriber<ListItem[]> getSubscriber() {
return Subscribers.create(new Action1<ListItem[]>() {
#Override
public void call(ListItem[] listItems) {
mDataset.clear();
mDataset.addAll(Arrays.asList(listItems));
notifyDataSetChanged();
}
});
}
......

As Hissain describes above,
you need to maintain a reference to the list
Here's how I got it to work:
Let the list being sent to the adapter be set as an instance member in the activity
In the logic that performs a change to the data, make sure it updates the same list instance that the activity passed to the adapter
Then calling .notifyDataSetChanged(); worked
Remember that listView position starts at 1, so you will have to do (listViewPosition - 1) for your your java.util.List

I dont have much reputation to comment on Mr. Hissain answer.It is correct but I want to mention one more thing that reference to the list should not change. If data source underlying is changing, dont change the reference to new list. Actions only need to be done on the same list object. To do the same,clear the list using clear() and then add data to the same list using add() or addALL() and then call notifyDataSetChanged(). eg.
On first initialization of the list
list = dataSource.getList();
then one can add and remove the content from the list and call notifyDataSetChanged() it works fine but if in the code, one tries to change the reference to the other object. Like
list = dataSource.getList();
where getList() returns the new list everytime, hence the reference changes to some other list object and calling notifyDataSetChnaged does not have impact on the list.But if getList() returns the same list object, it works fine.

If everything you set fine and still not working then your list...
Is it Mutablekind of the List or not...!
private val demoList: MutableList<AnyClass> = mutableListOf()
once you define your list like above mutable manner then you can get the method
.add
.addAll
.remove
etc...
else if you have created normal list then that will not work as notifyDataSetChanged

Android - How to work with nested ListViews

this is my first question on this site and I am also new to Android. I am creating an application using an online API. I am working with this API in XML and parsing the responses into ListViews. I have reached a point where I would like to select an item from a ListView in one activity and send that information to the next activity along with another ListView containing more information for the selected item. As an example, one activity has a list of bands. Clicking on the band name will bring up the band name and a list of tour dates on the next activity. According to my API, the band's ID number is needed to access the bands tour information I am trying to pass the ID number as a search parameter but cannot get this to work. I did manage to find a decent tutorial on androidhive.info but cannot seem to be able to apply these techniques. The doInBackground() method is where my app is hanging up.
ListView lv = getListView();
lv.setOnItemClickListener(new OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String displayName = ((TextView) view.findViewById(R.id.tvDisplayName)).getText().toString();
String onTourUntil = ((TextView) view.findViewById(R.id.tvOnTourUntil)).getText().toString();
String identification = ((TextView) view.findViewById(R.id.tvId)).getText().toString();
// Starting new intent
Intent in = new Intent(getApplicationContext(), SingleArtistActivity.class);
in.putExtra(KEY_DISPLAY_NAME, displayName);
in.putExtra(KEY_ID, identification);
in.putExtra(KEY_ON_TOUR_UNTIL, onTourUntil);
new AsyncDownload().execute(identification);
startActivity(in);
}
});
}
private class AsyncDownload extends AsyncTask<String, String, String> {
ProgressDialog pDialog;
#Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(ArtistsSearchActivity.this);
pDialog.setMessage("Please Wait...");
pDialog.setCancelable(false);
pDialog.show();
}
#Override
protected String doInBackground(String... params) {
Log.v(TAG, "query is" + params[0]);
String result = new ArtistCalendarHelper().getXml(params[0]);
return result;
}
My AsyncDownload class is called in my onClickListener. The class calls a helper that contains the URL and API key.
public class ArtistCalendarHelper {
private static final String TAG = "ArtistCalendarHelper";
private static final String SONGKICK_URL = "http://api.songkick.com/api/3.0/artists/";
private static final String API_KEY = "yIekMi1hQzcFheKc";
public String getXml(String identification) {
HttpClient httpclient = new DefaultHttpClient();
String getParameters = "";
try {
getParameters = URLEncoder.encode(identification, "UTF-8")
+ "/calendar.xml?apikey=" + URLEncoder.encode(API_KEY, "UTF-8");
} catch (UnsupportedEncodingException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
String url = SONGKICK_URL + getParameters;
// Prepare a request object
HttpGet httpget = new HttpGet(url);
// Execute the request
HttpResponse response;
These methods worked for obtaining the bands name in an initial search. How could this be changed to perform a search for tour information with an argument retrieved from a ListView?
Is this different from getting a search query from an EditText field? I didn't think there would be much of a difference. I have tried to include the affected code. I am not sure how much code I should provide.

you can try this:
step 1. Intent in = new Intent(getApplicationContext(), SingleArtistActivity.class);
in.putExtra(KEY_DISPLAY_NAME, displayName);
in.putExtra(KEY_ID, identification);
in.putExtra(KEY_ON_TOUR_UNTIL, onTourUntil);
// new AsyncDownload().execute(identification); dont start the net request here
startActivity(in);
step 2.
put on request url method in second Activity's on create() method
public class SingleArtistActivity{
onCrete(){
...
new AsyncDownload().execute(identification);
}
in SingleArtistActivity, instance a empty Adapter, call method : listView.setAdapter(adapter), then the view will show but the listview is empty ,no data will display, but the url request is working in background.
}
step 3:
when the AsyncTask return the data , put the data into a List data;
then call the adapter.notifyDataSetChanged()
the listview will reload the apapter again , the data will be display in the listview

I think there is a mistake here:
// Starting new intent
Intent in = new Intent(getApplicationContext(), SingleArtistActivity.class);
in.putExtra(KEY_DISPLAY_NAME, displayName);
in.putExtra(KEY_ID, identification);
in.putExtra(KEY_ON_TOUR_UNTIL, onTourUntil);
new AsyncDownload().execute(identification);
startActivity(in);
I guess you want to load the data with AsyncDownload then show them in SingleArtistActivity.class.
So you should put these code in SingleArtistActivity.java.
You should call new AsyncDownload().execute(identification);in onCreate() or onResume() of SingleArtistActivity.java ;
and setAdapter in onPostExecute of your AsyncDownload class.
like these:
#Override
protected void onPostExecute() {
if(pDialog != null && pDialog.showing()) {
pDialog.dismiss();
}
YourAdapter adapter = new Adapter(yourdata);
setListAdapter(adapter);
}

how to append latest data to custom base adapter list view in android?

I have implemented an application with Custom base adapter for display data in list view.In my application i have displayed some content to list view by using Custom base adapter that content will come from web service.I have used a button for get the latest data from service.when i get the latest data from service then i would like to append the latest data to list view at bottom without deleting previous data in list view.
I have implemented my application as follows:
result = new ParseXml().convertMessages(new Model().getMessages("0"));
count = Integer.parseInt(result.get(0).getMessageID());
((Button)findViewById(R.id.oldMessagesButton)).setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
fetchNewMessages();
}
});
protected void fetchOldMessages() {
// TODO Auto-generated method stub
waitProgreess = ProgressDialog.show(this, "Please wait", "Loading...");
new Thread() {
public void run() {
try {
Thread.sleep(800);
} catch (InterruptedException e) {
}
newmessageHandler.sendEmptyMessage(0);
}
}.start();
}
private Handler newmessageHandler = new Handler() {
public void handleMessage(Message msg) {
super.handleMessage(msg);
Log.v("000000", "count :"+count);
if(count>0){
newmsgResult = new ParseXml().convertMessages(new Model().getNewMessages(""+count));
CustomeAdapter adapter = new CustomeAdapter(GetMsgsScreen.this,newmsgResult);
lst.setAdapter(adapter);
adapter.notifyDataSetChanged();
count=Integer.parseInt(newmsgResult.get(oldmsgResult.size()-1).getMessageID());
}
waitProgreess.dismiss();
}
};
I have implemented the above code based on user clicking on button count value will be send to service then get latest from service.When i get the latest list from servie the that list would like append to list view.
from the above code i can get only latest previous are deleting.
How can i append latest data(list) to listview in my above case?
please any body help me....

CustomeAdapter adapter = new CustomeAdapter(GetMsgsScreen.this,newmsgResult);
define this adapter andnewmsgResult at top of your class..not a local variable inside a class..
Now, whenever you want to update the data in list view, update the values/data in newmsgResult and call adapter.notifyDataSetChanged()

I think it is happening because you are creating a new custom adapter every time you are getting new messages.. in this line
CustomeAdapter adapter = new CustomeAdapter(GetMsgsScreen.this,newmsgResult);
dont do this and try to use adapter.add(Newmessage); you can use array list to make work easier
ok.. you should have an add function in your custom adapter class for that.. you can do so by adding this to your custom adapter class
private void customadd(String newmsg)
{
//ArrayList<String> msg=new List<String>; create this array list as a source to your adapter
msg.add(newmsg);
adapter.notifyDataSetChanged();
}

Initially load the your list view with customAdapter using result(By assumption result is arraylist)
CustomeAdapter adapter = new CustomeAdapter(GetMsgsScreen.this,result);
lst.setAdapter(adapter);
once you have new value no need to create new result and adapter object, simply append you result in your adapter object,
result.add("append your new result");
then simply adapter.notifyDataSetChanged();

Dont create a new adapter. Keep the original one and pass the new data to it for appending it.